Category Archives: Xamarin Forms

Restructuring the Xamarin.Forms Shell Default App Template…

Let’s restructure the default project Template for Xamarin.Forms Shell Apps provided by Visual Studio 2019, clean it up, optimize it for the best use of Shell features. 😉

To be more detailed when you create a fresh Xamarin.Forms Shell app, in Visual Studio 2019, you get a certain default template app project provided by VS2019, let me show you how to restructure it in a clean and optimized manner for best use of features, performance and code structure.

Xamarin.Forms Shell is Awesome…

but I had quite a bit confusion understand the reason behind it and the bells and whistles of it, let me explain! So I’ve been working extensively with Xamarin framework for over 4 years now, and I’m confident to say that I have expertized myself on the best use of it. 😀

The way Xamarin.Forms Shell was marketed for was to provide a better alternative for dealing with Master Detailed or Tab Page based Xamarin.Forms Apps. This really made sense to me, since I knew how troublesome or the complexity we have to deal with in those scenarios.

Template Project mess?!

I went through the documentation, followed up on some demo code the community had shared, and once I was confident, it was time to get my hands dirty. So I created a fresh new Xamarin.Forms Shell project in Visual Studio 2019, and started going through the code.

It was a messy chaos! Since the first line of code, it was confusing, with many different Xamairn.Forms implementation practices all over the place in both UI and C# code behind, Xamarin.Forms Classic and Shell navigation mixed up in all over the project and so on. Took me quite a while to get a hold of it. 😦

This is quite a bad set up for a Template project, could be very disorienting for anyone who’s fresh starting off with Xamarin.Forms Shell, let alone Xamarin.Forms itself.

But why?

My best bet is that they wanted to give the perception to the developer that you can interchange and mix up as you like, Xamarin.Forms Classic bits and Shell bits. This is probably in a good intention, but for anyone who’s just starting to grasp it, could be very confusing, mixing up everything together in a template project.

Sure Xamarin.Forms Classic and Shell are completely interchangeable elements, but for a template, you need to give a clear, straight forward way to get started for anyone.

Ze Solution!

So my solution, is to adopt only Xamarin.Forms Shell related implementation, features, and practices into the default Template, so it gives a clear, easy to understand, straight forward view of using Xamairn.Forms Shell to build apps. Thinking in terms of simplest terms, decoupled components with clean and readable code, we need to reflect the best practices of Xamarin.Forms in the Template. 😉

So here I am sharing my journey of restructuring the default project Template for Xamarin.Forms Shell Apps step by step… Also I would like to share this as a guide to fixing up an existing messy project, with all the good coding practices in mind when it comes to Xamarin.Forms! 😀

Default Template Project…

Let’s take a proper look at the what you get fresh out of the box when you create a new Xamarin.Forms Shell project in VS2019 as of now,

So as you can see it promotes MVVM structure in the project, with Models, Views, and ViewModels separated, while also having a separate DataStore service. The basic functionality of this app is to Write text note items with a Title and Description and save them in the memory.

The app consists of ItemsPage where it shows all the text notes added, then ItemDetailsPage where you can view each of the notes, then the NewItemPage which is a modal page allowing you to add new text items, finally a simple AboutPage with a little intro to the Xamarin.Forms Shell.

Issues need Fixes…

Now let me walk you through some of the main problematic bits I found in this template project, one by one…

BindingContext init() inconsistent…

The BindingContext initialization with the ViewModel instance it all over the place, while some pages having it in code behind in the constructor.

And others having it in the XAML itself as shown below..

This should be unified either to code behind Constructor or the other only.

NewItemsPage, no ViewModel!?

For the NewItemsPage, there’s no ViewModel available, and it sets the BindingContext to itself as shown below…

This needs to be modified with its own ViewModel class, and move these data functions into it.

Missing Shell  Query Parameters…

The recommended way to pass data between pages in Xamarin.Forms Shell is to use Query Parameter strings, but this is not reflected in the Template project at all. As you can see below, it uses a tightly coupled Constructor parameter object passing instead.

This needs to be changed to use Xamarin.Forms Shell query parameters, as recommended.

Need to unify Color Resources…

Apart from the global Colors and Styles resources defined in the App.xaml, there are page level resources added as well in some pages.

This should be removed and switched to use global context Colors for better re-usability and reduce repetition of code.

Classic Xamarin.Forms Navigation!? Why!?

Now this was a serious WHY? moment I had when I first saw this, no where in the template project is using actual Xamarin.Forms Shell Route based navigation.

All over the project you will see the Classic Xamarin.Forms Navigation being used.

This needs to be changed to use the actual Shell Route based navigation.

To make it worse, for Modal pages, it implements a very bad practice of forcefully pushing the Navigation Bar on top of it. 😮

Now you can see why I have complained it’s a messy mix of everything, which needs cleaning up with a proper project structure.

Let the Restructuring begin!

Let me walk yol through the whole restructuring process I did step by step, so that you get a clear idea how to make changes in your own projects. Also have pushed this up in my Github repo, if you’re interested in taking a peak.

hosted on github:
github.com/UdaraAlwis/XFShellTemplateDemoApp

Alright then let’s on ahead…

Step 1: Cleaning up Colors and Styles…

Let’s get rid of the page level Color values and move them to the App.xaml, allowing them to be shared on an app global context, increasing re-usability and removing redundancy.

<!--
	Application Styles and Resources
-->
<Application.Resources>
	<ResourceDictionary>
		<Color x:Key="Primary">#2196F3</Color>
		<Color x:Key="Accent">#96d1ff</Color>
		<Color x:Key="LightTextColor">#999999</Color>
	</ResourceDictionary>
</Application.Resources>

Make sure to keep one key for each color value, and share that in all the required elements. Now we have a much cleaner XAML! 😉

Step 2: BaseViewModel to Infrastructure!

The BaseViewModel.cs class is not actively being instantiated but provides a base for the ViewModels of the project, so it would make sense to move out the BaseViewModel.cs class into a separate folder called, Infrastructure.

Also let’s do a bit of code refactoring inside the BaseViewModel, with the field naming, such as private fields, by adding _fieldName format as a good C# code standard.

Step 3: BindingContext in the Constructor()

Let’s have the ViewModel instantiation and its assigning to the Page.BindingContext, inside the Constructor() of each page. Yep, and don’t forget to remove the XAML set up added in the default template. 😉

public partial class ItemsPage : ContentPage
{
    private readonly ItemsViewModel _viewModel;

    public ItemsPage()
    {
        InitializeComponent();

        BindingContext = _viewModel = new ItemsViewModel();
    }
    
    ...
}

This would give better control over the ViewModel’s object instance. The private field will be named accordingly with the “_” prefix, and kept as a private readonly field, since its only going to be instantiated once in the Constructor itself. Make sure to propagate the same for all the Pages in the project.

Step 4: Clean up ItemDetailViewModel!

We need to clean up the ItemDetailViewModel, to be stand-alone and loosely coupled. This will also help us in implementing a proper Shell Route based navigation later.

Let’s convert the Item property into a full fledged property with a private backing field, GETter and SETter. 😉 In the constructor, get rid of the parameter passed in, and let’s assign a dummy value to it as default value.

public class ItemDetailViewModel : BaseViewModel
{
	private Item _item;

	public Item Item
	{
		get => _item;
		private set
		{
			SetProperty(ref _item, value);
			Title = _item?.Text;
		}
	}

	public Command LoadItemCommand { get; set; }

	public ItemDetailViewModel()
	{
		var item = new Item
		{       
                        Id = Guid.NewGuid().ToString(),
			Text = "Sample Item",
			Description = "This is an item description."
		};

		Item = item;

		LoadItemCommand = new Command<string>(async (itemId) => await LoadItem(itemId));
	}

	private async Task LoadItem(string itemId)
	{
		Item = await DataStore.GetItemAsync(itemId);
	}
}

Apart from the Item property, I have added a new Command, which will load the Item details object from the DataStore service.

Now that a well structured, clean ViewModel eh! Next let’s handle the parameter that we’re suppose to pass from ItemsPage to ItemDetailPage…

Step 5: Setting up Query Parameters…

As a part of the previous step, we need to handle the selected Item object that’s being passed into the ItemDetailPage. We’re going to handle this properly with Xamarin.Forms Shell Query parameters. So let’s pass the Id value of the selected Item object, as a query parameter into the page as follows, with the QueryProperty attribute.

[QueryProperty(nameof(ItemId), "itemid")]
public partial class ItemDetailPage : ContentPage
{
	private readonly ItemDetailViewModel _viewModel;
	private string _itemId;

	public string ItemId
	{
		get => _itemId;
		set => _itemId = Uri.UnescapeDataString(value);
	}
	
	...
}

Here we’re maintaining ItemId string property in the Page, where Shell we set the query value into during the navigation.

Do not forget to fire up the LoadItemCommand in the ViewModel of the page, with the ItemId that we acquired during navigation.

...
public partial class ItemDetailPage : ContentPage
{	
	...	
	protected override void OnAppearing()
	{
		base.OnAppearing();

		_viewModel.LoadItemCommand.Execute(ItemId);
	}
}

Alright, then let’s fix the navigation bits next…

Step 6: Use proper Shell Navigation!

Instead of using Xamarin.Forms Classic navigation, let’s migrate all the Navigation bits to proper Xamarin.Forms Shell Route based Navigation yeah!

Let’s start by registering the Page routes, that we use for navigation. Preferably using lower case letters for all the routes.

public partial class AppShell : Xamarin.Forms.Shell
{
	public AppShell()
	{
		InitializeComponent();

		Routing.RegisterRoute("itemdetailpage", typeof(ItemDetailPage));
		Routing.RegisterRoute("newitempage", typeof(NewItemPage));
	}
}

Then update all the navigation bits to use Shell route based navigation…

...
public partial class ItemsPage : ContentPage
{    
    ...
    private async void OnItemSelected(object sender, SelectedItemChangedEventArgs args)
    {
        ...

        await Shell.Current.
                    GoToAsync($"/itemdetailpage?itemid={item.Id.ToString()}");
        ...
    }
}

Now, that’s a proper Shell Navigation in action!

Step 7: Set up NewItemViewModel!

NewItemPage does not have a ViewModel created against it, in order to maintain a proper MVVM structure we need to move all the code behind bits in NewItemPage.xaml.cs into the NewItemViewModel as follows…

public class NewItemViewModel : BaseViewModel
{
    private Item _item;

    public Item Item
    {
        get => _item;
        set
        {
            SetProperty(ref _item, value);
        }
    }

    public NewItemViewModel()
    {
        var item = new Item
        {
           ...
        };

        Item = item;
    }
}

The in the page constructor we assign the instance of this ViewModel to the BindingContext, and you’re done..

Step 8: Use proper Modal Navigation!

The NewItemPage is treated as a Modal page, we should use Shell.PresentationMode instead of classic Navigation.PushModalAsync() for navigating to Modal pages.

First of all make sure we’re navigating to the NewItemPage properly using Shell Route navigation as follows,

...
public partial class ItemsPage : ContentPage
{    
    ...
    private async void AddItem_Clicked(object sender, EventArgs e)
    {
        await Shell.Current.GoToAsync($"/newitempage");
    }
}

Next we set up Shell.PresentationMode property in the NewItemPage to render the page navigation as the Modal page we expect it to be, using ModalAnimated value.

<ContentPage
    x:Class="XFShellTemplateDemoApp.Views.NewItemPage"
    xmlns:ios="clr-namespace:Xamarin.Forms.PlatformConfiguration.iOSSpecific;assembly=Xamarin.Forms.Core"
    ios:Page.UseSafeArea="true"
    Shell.PresentationMode="ModalAnimated">

	<!--  Content of the Page  -->
	
	... 

</ContentPage>

Also we should set up the UseSafeArea property for iOS to ignore the iPhone notch, since Modal page overlays the whole app window.

Finally, let’s get rid of the NavigationBar based buttons and use Page Content based Buttons, and modify the UI layout accordingly.

<ContentPage
    x:Class="XFShellTemplateDemoApp.Views.NewItemPage"
    Shell.PresentationMode="ModalAnimated">

    <ContentPage.Content>
        <Grid Margin="0" Padding="0">

            ...

            <StackLayout Padding="15" Orientation="Horizontal">
                <Button
                    BackgroundColor="{StaticResource Primary}"
                    Clicked="Cancel_Clicked"
                    HorizontalOptions="FillAndExpand"
                    Text="Cancel"
                    TextColor="White" />
                <Button
                    BackgroundColor="{StaticResource Primary}"
                    Clicked="Save_Clicked"
                    HorizontalOptions="FillAndExpand"
                    Text="Save"
                    TextColor="White" />
            </StackLayout>

            ...

        </Grid>
    </ContentPage.Content>
</ContentPage>

I have created separate Cancel and Save Buttons which is inside a StackLayout, which in return is inside in the parent Grid Layout where rest of the content resides.

...
public partial class NewItemPage : ContentPage
{    
    ...
    private async void Cancel_Clicked(object sender, EventArgs e)
    {
        await Shell.Current.Navigation.PopModalAsync();
    }
}

For dismissing the page we can stick to PopModalAsync() call in the Navigation stack, since Shell doesn’t have it’s own for that.

Step 9: Overall code quality clean up…

Apart from all these structural changes, another aspect I heavily focused on was, the readability of the code and maintaining proper coding standards, down to the variable naming.

It’s important to properly write the code with all these little details in mind so that its easy to read and understandable by anyone who try to understand the code.

Alright then, with that I conclude the restructuring!

Restructured Template Project…

Aaand let’s take a proper look at what we got at the end after the extensive restructuring of the Xamarin.Forms Shell Template project in VS2019,

Here’s it in action in iOS!

in Android!

Once again you may find the whole project code is hosted on my Github repo,

hosted on github:
github.com/UdaraAlwis/XFShellTemplateDemoApp

Feel free to fork it out and use it as anyway you wish, may be even for a starter pack for your Xamarin.Forms Shell App development journey! 😉

Conclusion!

Well that concludes my journey of restructuring the Xamarin.Forms Shell default project template in VS2019, for the best use of Shell features, performance and optimized clean code.

Xamarin.Forms Shell is actually an awesome new paradigm to build Xamarin.Forms app, but honestly the VS2019 Template project could really use some proper restructuring for making it easier and straight forward for the beginners to start off. 😉

Share the love! 😀 Cheers yol!

Publishing the Nuget of my Color Picker Control for Xamarin.Forms!

Let me share the journey of me publishing the Nuget Package of my interactive Color Picker Control for Xamarin.Forms that I built using SkiaSharp.

So some time back I built an Interactive and responsive Color Picker Control for Xamarin.Forms (Android, iOS, UWP) with a whole bunch of awesome features. On a Canvas with a beautiful Color spectrum similar to a rainbow gradient effect spreading across, drag, drop, swipe and pan over the Canvas to pick the Color you need easily, in a fun-to-use interactive experience. Built from pure Xamarin.Forms based on SkiaSharp, lightweight and fast!

Backstory…

In my previous blog post I shared with you guys how I built my interactive Color Picker Control for Xamarin.Forms, https://theconfuzedsourcecode.wordpress.com/2020/02/26/i-built-an-interactive-color-picker-control-for-xamarin-forms/

Since then I had been adding a whole bunch of extra feature to this Color Picker Control I built, so I thought it was a good idea to publish it as a Nuget Package and share with everyone! 😀

So this time, let me share my journey of implementing more advanced features and publishing the Nuget Package of my Color Picker Control for Xamarin.Forms! 😉

Some thought…

So before I isolated my Color Picker Control into a stand alone reusable package, I wanted to make sure that I maintain my philosophy of building Plugins. This would definitely have a big impact on your Users who will will be using these Plugins to build their apps, therefore I’ll share the tick list that I consider as important as follows…

Plug and Play: The plugin should easy to set up with. Do not force Devs to set up any dependencies or property values by themselves. The properties and behaviors of the Plugin should have default values assigned to them.

Customization: It should be easy and straight forward for the Devs to customize the appearance or the behaviors of the Plugin. In some case this might be limited, but you must build the Plugin in a way it make it easy as much as possible.

Embedded: In the case of UI Element Plugins, you should make it easy to be embedded into any Layout structure, being able to inherit the Parent Layout’s behaviors and values, without overriding or disrupting them.

Keep it Light: Make the Plugin as lightweight as possible, give the Dev the chance to choose which assemblies to be included in the plugin. Remove unnecessary references or dependencies from your Plugin core, so it’s light weight as possible.

Performance First: It shouldn’t cause any performance bottleneck, therefore from scratch you must build the Plugin with performance in mind. Constantly check for performance improvements during the development of your Plugin.

So may be go over this list before you build or release a Plugin for the public! 😉 Alright, with all those principles in mind, let’s move ahead…

The Features!

So here are the features that are already available in the Color Picker Control that I built which I had shared from my previous blog post…

  • Picked Color: The Property that allows Users to retrieve the Color values that’s selected from the Color Picker. This value is only a Get Property.
  • Picked Color Changed Event: The Event that fires up every time the PickedColor Value is changed during Color selection. You can subscribe to this event and observe the behavior.

Since my venture into this Color Picker Plugin I had a few ideas in mind as improvements or rather add as extra features, rather than just being a UI Element which allows you to pick a color on a beautiful spectrum! 😉 So here are the extra features that I’ll be building up into it..

  • Change the Available Base Colors List: You can set the primary list of Colors where the gradient spectrum will be rendered from. So choose the base colors you want to be populated as you wish and it will be rendered on the Color Picker.
  • Change the Color List Flow Direction: You will be able to change the direction of the flow of the colors on the canvas, where it be Horizontal flow or a Vertical flow of the color spectrum. Further more Horizontally being starting off the flow from left to right, and Vertically being top to bottom.
  • Change the Color Spectrum Style: You will be able to change the style of the Color Spectrum gradient, the rendering combination of base colors (Hue), or lighter colors (Tint) or darker colors (Shade). You’ll be able to set it with different order as well, ex: Hue Colors, Shade Colors, Tint Colors or Tint Colors, Hue Colors, Shade Colors, etc..
  • Change the Appearance of the Pointer: The white color circle that is used as the Picker Pointer on the Canvas, should be able to customized based on its Diameter or Thickness of the Circle border. Another nice addition would be to allow user to set the position of the Pointer as they wish.

Alright, now that we listed down the new intended feature set that I’m planning to ship out with my Color Picker Control, let’s get down to building it… 😀

Sneak Peak!

Just to give a little glimpse of the awesomeness I ended up building and publishing… 😀 behold the Color Picker Control for Xamarin.Forms!

Pretty awesome eh! 😉 I have moved out of my previous repo to a new standalone repo in github, since I’m publishing this as a package. Therefore all the new development will be done in this repository.

Project hosted on github:
https://github.com/UdaraAlwis/XFColorPickerControl

So feel free to take a look in there before we continue… 😉

Time to Build!

Since I already explained in my previous blog post how I built my Color Picker Control from scratch step by step, I won’t be repeatedly going through same code bits in this post, but rather focus on the new changes and features only.
If you haven’t read that one yet, then I would recommend you take a peak there first, I built an Interactive Color Picker Control for Xamarin.Forms! And continue here…

I named the Solution as Udara.Plugin.XFColorPickerControl, and in return I intend to keep the Package reference with the same naming. I am using Visual Studio 2019 on Windows 10 here as my development environment.

I have created a VS Solution with a .NET Standard 2.0 Library which will hold the UI Control in place, with the naming ColorPicker. You can see I have added the dependencies of the Plugin, with Xamarin.Forms and SkiaSharp.Views.Forms packages. 😉

Notice the pure Xamarin.Forms DemoApp project inside the Demo folder that I have added to the same solution? That is for testing and showcasing the Plugin’s use, also as a reference point for anyone who wants to learn how to use the Plugin in many different ways, this attached DemoApp could come handy. 😀

The ColorPicker.xaml is the UI Element that users will be using under the namespace Udara.Plugin.XFColorPickerControl.ColorPicker in their XAML or C# code for building the UI. Here’s base skeleton implementation of the ColorPicker.xaml.cs, which all the core implementation will be taking place…

namespace Udara.Plugin.XFColorPickerControl
{
    [XamlCompilation(XamlCompilationOptions.Compile)]
    public partial class ColorPicker : ContentView
    {
        public ColorPicker()
        {
            InitializeComponent();
        }

        // Implementation goes here
    }
}

Next let’s get into the implementation of Features one by one as I discussed before…

Building the Features!

So I’m going to use the same code for the two features that I already implemented in my previous blog post, Picked Color and Picked Color Changed Event feature that’s represented by PickedColor Property and PickedColorChanged Event Handler.

[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class ColorPicker : ContentView
{
	/// <summary>
	/// Occurs when the Picked Color changes
	/// </summary>
	public event EventHandler<Color> PickedColorChanged;

	public static readonly BindableProperty PickedColorProperty
		= BindableProperty.Create(
			nameof(PickedColor),
			typeof(Color),
			typeof(ColorPicker));

	/// <summary>
	/// Get the current Picked Color
	/// </summary>
	public Color PickedColor
	{
		get { return (Color)GetValue(PickedColorProperty); }
		private set { SetValue(PickedColorProperty, value); }
	}
	
	...
}

Now considering the rest of the features that I discussed in the beginning, all those features can be implemented and exposed via Bendable Properties, and handling the Property Changed events internally to react for any changes requested during run time.

[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class ColorPicker : ContentView
{
    ...
 
    public static readonly BindableProperty PropertyNameProperty
        = BindableProperty.Create( 
        ... 
        
            validateValue: (bindable, value) =>
            {
                // validate value
                return (..);
            },
            
            propertyChanged: (bindable, value, newValue) =>
            {
                if (newValue != null)
                    // action on value change
                else
                    // handling null values
                    ((ColorPicker)bindable).PropertyNameProperty = default;
            });
        );
 
    public type PropertyName
    { ... }
 
    ...
}

All the Bindable Properties are safeguarded with validations as you see above. I have added an extra layer of protection against unnecessary null values being set up, by defaulting the property value to default of itself. You can check the full implementation of each of these Properties on the github repo itself. github.com/UdaraAlwis/XFColorPickerControl Let’s begin..

Feature: BaseColorList

Bindable Property, BaseColorList: Change the available base Colors on the Color Spectrum, of the Color Picker. This will take a List of strings of Color names or Hex values, which is held in an IEnumerable as show here, also I have set up the fallback default values with the rainbow color spectrum.

[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class ColorPicker : ContentView
{
    ...

    public static readonly BindableProperty BaseColorListProperty
        = BindableProperty.Create( ... );

    public IEnumerable BaseColorList
    { ... }

    ...
}

This Property is then consumed during the SkiaSharp rendering cycle as follows, where as we’re using the Xamarin.Forms built in ColorTypeConverter to parse the string color values to actual Color objects and then to SKColor objects, which is then used to render the render the color spectrum on the Color Picker Control. 😀

...
    private void SkCanvasView_OnPaintSurface
                   (object sender, SKPaintSurfaceEventArgs  e)
    {
        ...
         
        // Draw gradient rainbow Color spectrum
        using (var paint = new SKPaint())
        {
            paint.IsAntialias = true;
 
            // Initiate the base Color list
            ColorTypeConverter converter = new ColorTypeConverter();
            System.Collections.Generic.List<SKColor> colors = 
                new System.Collections.Generic.List<SKColor>();
            foreach (var color in BaseColorList)
                colors.Add(((Color)converter.
		          ConvertFromInvariantString(color.ToString())).ToSKColor());
				
            ...
        }
    }
...

Pretty straight forward eh! Let’s see how you could use this as a developer.

How to use?

You can easily use this feature in XAML as follows, by accessing ColorPicker.BaseColorList property and setting up the list of color values you prefer as hex values or with pre-defined color value names.

<xfColorPickerControl:ColorPicker
	x:Name="ColorPicker"
	...	>
	<xfColorPickerControl:ColorPicker.BaseColorList>
		<x:Array Type="{x:Type x:String}">
			<!--  Yellow  -->
			<x:String>#ffff00</x:String>
			<!--  Aqua  -->
			<x:String>#00ffff</x:String>
			<!--  Fuchsia  -->
			<x:String>#ff00ff</x:String>
			<!--  Yellow  -->
			<x:String>#ffff00</x:String>
		</x:Array>
	</xfColorPickerControl:ColorPicker.BaseColorList>
</xfColorPickerControl:ColorPicker>

If you prefer in C# code, you can easily do as as well, a list of string values of the colors…

ColorPicker.BaseColorList = new List<string>()
{
	"#00bfff",
	"#0040ff",
	"#8000ff",
	"#ff00ff",
	"#ff0000",
};

Here’s some action…

Feature: ColorFlowDirection

The Bindable Property, ColorFlowDirection: Change the direction in which the Colors are flowing through on the Color Spectrum, of the Color Picker. This will allow you to set whether the Colors are flowing through from left to right, Horizontally or top to bottom, Vertically. I have defined an Enum type which will represent this type of course.

namespace Udara.Plugin.XFColorPickerControl
{
    public enum ColorFlowDirection
    {
        Horizontal,
        Vertical
    }
}

Let’s create our ColorFlowDirection Bindable Property based on that,

[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class ColorPicker : ContentView
{
    ...

    public static readonly BindableProperty ColorFlowDirectionProperty
        = BindableProperty.Create( ... );

    public ColorFlowDirection ColorFlowDirection
    { ... }

    ...
}

The default value will be set as ColorFlowDirection.Horizontal, and if the User changes value during run time, it will fire up a new SkiaSharp rendering cycle of the Canvas, effectively rendering the spectrum accordingly to the new color value, which is handled in the rendering logic as below…

...
    private void SkCanvasView_OnPaintSurface
                   (object sender, SKPaintSurfaceEventArgs  e)
    {
        ...
        
            // create the gradient shader between base Colors
            using (var shader = SKShader.CreateLinearGradient(
                new SKPoint(0, 0),
                ColorFlowDirection == ColorFlowDirection.Horizontal ?
                    new SKPoint(skCanvasWidth, 0) : 
                    new SKPoint(0, skCanvasHeight),
                colors.ToArray(),
                null,
                SKShaderTileMode.Clamp))
            {
                paint.Shader = shader;
                skCanvas.DrawPaint(paint);
            }
            
        ...
    }
...

The trick here is to configure the SKShader.CreateLinearGradient() method’s start and end coordinate parameters, which governs the direction in which the gradient effect will be drawn with the list of colors, thus rendering the color list from left to right or top to bottom. As you can see for Horizontal effect, we use SKPoint (0,0) to SKPoint(<canvasWidth>, 0) by using the corner most value on the X axis for the end coordinates, the same pattern is used for Vertical effect with bottom most value on the Y axis.

Here how to consume this feature as a developer…

How to use?

You can easily use this feature in XAML, by accessing ColorPicker.ColorFlowDirection property and setting Horizontal or Vertical option as you prefer…

<xfColorPickerControl:ColorPicker
	x:Name="ColorPicker"
	ColorFlowDirection="Horizontal"
	...	>
</xfColorPickerControl:ColorPicker>

If you prefer in C# code, use the ColorFlowDirection.Horizontal or Vertical option…

ColorPicker.ColorFlowDirection =
	Udara.Plugin.XFColorPickerControl.ColorFlowDirection.Horizontal;

Here’s some action…

Feature: ColorSpectrumStyle

The Bindable Property, ColorSpectrumStyle: Change the Color Spectrum gradient style, with the rendering combination of base colors (Hue), or lighter colors (Tint) or darker colors (Shade). If you’re not familiar with these technical terms, here’s a clear illustration of comparison of Hue, Shade, and Tint of Colors.

We need to make sure our Color Picker is able to deliver to this kind of requirement, having darker or lighter colors of the given base colors on the Color Picker Spectrum. So I’ve created an Enum type which will consist of all the possible combinations of Hue, Shade and Tint colors based on the available Base Colors, that would facilitate this feature.

namespace Udara.Plugin.XFColorPickerControl
{
    public enum ColorSpectrumStyle
    {
        HueOnlyStyle,
        HueToShadeStyle,
        ShadeToHueStyle,
        HueToTintStyle,
        TintToHueStyle,
        TintToHueToShadeStyle,
        ShadeToHueToTintStyle
    }
}

Let’s create our ColorSpectrumStyle Bindable Property based on that,

[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class ColorPicker : ContentView
{
    ...

    public static readonly BindableProperty ColorSpectrumStyleProperty
        = BindableProperty.Create( ... );

    public ColorSpectrumStyle ColorSpectrumStyle
    { ... }

    ...
}

I will be setting ColorSpectrumStyle.HueToShadeStyle as the default value for this property, any changes to this value during run time will kick start a new refresh draw on the Color Spectrum, which is handled in the rendering logic as below…

...
    private void SkCanvasView_OnPaintSurface
                   (object sender, SKPaintSurfaceEventArgs  e)
    {
        ...
         
        // Draw secondary gradient color spectrum
        using (var paint = new SKPaint())
        {
            paint.IsAntialias = true;
 
            // Initiate gradient color spectrum style layer
            var colors = GetSecondaryLayerColors(ColorSpectrumStyle);
			
            ...
        }
    }
...

Over here, we’re retrieving the list of colors based on the ColorSpectrumStyle value, which is a combination of Transparent, Black and White colors, which will be used to draw the secondary gradient layer. GetSecondaryLayerColors() will be returning the appropriate list of secondary colors that matches the ColorSpectrumStyle requested as follows.

...
    private SKColor[] GetSecondaryLayerColors(ColorSpectrumStyle colorSpectrumStyle)
    {
        ...
        
        if (colorSpectrumStyle == GradientColorStyle.DarkToColorsToLightStyle)
        {
            return new SKColor[]
            {
                SKColors.Black,
                SKColors.Transparent,
                SKColors.White
            };
        }
        
        ...
    }
...

I’m maintaining a simple If-else block chain which will check for the ColorSpectrumStyle value available and return the appropriate list of colors back. Quite straight forward! 😉

Now here’s how you use this awesome feature…

How to use?

You can easily use this feature in XAML, by accessing ColorPicker.ColorSpectrumStyle property and setting the appropriate Style option as you prefer…

<xfColorPickerControl:ColorPicker
	x:Name="ColorPicker"
	ColorSpectrumStyle="TintToHueToShadeStyle"
	...	>
</xfColorPickerControl:ColorPicker>

If you prefer in C# code…

ColorPicker.ColorSpectrumStyle =
	Udara.Plugin.XFColorPickerControl.ColorSpectrumStyle.TintToHueToShadeStyle;

Here’s some action…

Feature: PointerRing Styling

As you can see there’s a pretty neat Pointer Ring that’s pointing the picked color position on the Color Picker, it would be nice to be able to customized this too eh! 😉

Therefore I have introduced four features for this,

  • PointerRingDiameterUnits
  • PointerRingBorderUnits
  • PointerRingPositionXUnits
  • PointerRingPositionYUnits

Alright, let’s walk through them one by one..

Feature: PointerRingDiameterUnits

The Bindable Property, PointerRingDiameter: Changes the Diameter size of the Pointer Ring on the Color Picker. It accepts values between 0 and 1, as a representation of numerical units which is compared to the 1/10th of the longest length of the Color Picker Canvas. By default this value is set to 0.6 units.

[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class ColorPicker : ContentView
{
    ...
 
    public static readonly BindableProperty PointerRingDiameterUnitsProperty
        = BindableProperty.Create( ... );
 
    public double PointerRingDiameterUnits
    { ... }
    
    ...
}

This will be calculated against the longest length of Color Picker’s Canvas, whether it be Width or Height. The reason for adding another 1/10th of the value is to maintain the maximum size of the Pointer Ring, avoiding ridiculous sizing of the element. lol So the Precise calculation is as, Canvas Size (Height or Width) x PointerRingDiameterUnits x (1/10)
This value will render exactly to the same proportion against different screen sizes and DPs.

...
    private void SkCanvasView_OnPaintSurface
                   (object sender, SKPaintSurfaceEventArgs  e)
    {
        ...
         
        // Painting the Touch point
        using (var paint = new SKPaint())
        {
            ...
 
            var canvasLongestLength = (skCanvasWidth > skCanvasHeight) 
                    ? skCanvasWidth : skCanvasHeight;

            // Calculate 1/10th of the units value for scaling
            var pointerRingDiameterUnitsScaled = (float)PointerRingDiameterUnits / 10f;
            // Calculate against Longest Length of Canvas 
            var pointerRingDiameter = (float)canvasLongestLength 
                                                    * pointerRingDiameterUnitsScaled;

            // Outer circle of the Pointer (Ring)
            skCanvas.DrawCircle(
                _lastTouchPoint.X,
                _lastTouchPoint.Y,
                (pointerRingDiameter / 2), paintTouchPoint);

            ...
        }
    }
...

I’ve set up the skCanvas.DrawCircle() with the (pointerRingDiameter / 2) since it accepts radius value only for drawing the circle.

How to use?

You can easily use this feature in XAML, by accessing ColorPicker.PointerRingDiameterUnits property and setting the value against your Color Picker’s Width and Height.

<xfColorPickerControl:ColorPicker
    x:Name="ColorPicker"
    PointerRingDiameterUnits="0.6"
    ...    >
</xfColorPickerControl:ColorPicker>

If you prefer in C# code…

ColorPicker.PointerRingDiameterUnits = 0.6;

Here’s some action…

Feature: PointerRingBorderUnits

The Bindable Property, PointerRingBorderUnits: Changes the Border Thickness size of the Pointer Ring on the Color Picker. It accepts values between 0 and 1, as a representation of numerical units which is calculated against the diameter of the Pointer Ring. By default this value is set to 0.3 units.

[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class ColorPicker : ContentView
{
    ...
 
    public static readonly BindableProperty PointerRingBorderUnitsProperty
        = BindableProperty.Create( ... );
 
    public double PointerRingBorderUnits
    { ... }
    
    ...
}

This calculation executes against the Pointer Ring’s pixel diameter value as, (Pointer Ring Diameter in Pixels) x PointerRingBorderUnits, since this is dependent on the Pointer Ring’s diameter, we thickens the border inside that circle only. Basic technique here is to draw a Circle inside the Parent Circle, with the picked pixel point’s color, emulating the visual of a Ring.

...
    private void SkCanvasView_OnPaintSurface
                   (object sender, SKPaintSurfaceEventArgs  e)
    {
        ...
         
        // Painting the Touch point
        using (var paint = new SKPaint())
        {
            ...
 
            // Draw inner circle with picked color
            paintTouchPoint.Color = touchPointColor;

            // Calculate against Pointer Circle
            var pointerRingInnerCircleDiameter 
                          = (float)pointerRingDiameter 
                              * (float)PointerRingBorderUnits; 

            // Inner circle of the Pointer (Ring)
            skCanvas.DrawCircle(
                _lastTouchPoint.X,
                _lastTouchPoint.Y,
                ((pointerRingDiameter 
                        - pointerRingInnerCircleDiameter) / 2), paintTouchPoint);
            ...
        }
    }
...

I’ve set up the skCanvas.DrawCircle() with the calculation, ((pointerRingDiameter – pointerRingInnerCircleDiameter) / 2) since it accepts radius value only for drawing the circle.

How to use?

You can easily use this feature in XAML, by accessing ColorPicker.PointerRingBorderUnits property and setting the value against PointerRingDiameterUnits you have used.

<xfColorPickerControl:ColorPicker
    x:Name="ColorPicker"
    PointerRingBorderUnits="0.3"
    ...    >
</xfColorPickerControl:ColorPicker>

If you prefer in C# code…

ColorPicker.PointerRingBorderUnits = 0.3;

Here’s some action…

Feature: PointerRingPosition<X,Y>Units

The Bindable Property, PointerRingPosition<X,Y>Units: Changes the Pointer Ring’s position on the Color Picker Canvas programmatically. There are of two bindable properties PointerRingPositionXUnits and PointerRingPositionYUnits, which represents X and Y coordinates on the Color Picker Canvas. It accepts values between 0 and 1, as a presentation of numerical units which is calculated against the Color Picker Canvas’s actual pixel Width and Height. By default both the values are set to 0.5 units, which positions the Pointer Ring in the center of the Color Picker.

[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class ColorPicker : ContentView
{
    ...
 
    public static readonly BindableProperty PointerRingPositionXUnitsProperty
        = BindableProperty.Create( ... );
 
    public double PointerRingPositionXUnits
    { ... }
	
    public static readonly BindableProperty PointerRingPositionYUnitsProperty
        = BindableProperty.Create( ... );
 
    public double PointerRingPositionYUnits
    { ... }
 
    ...
}

This calculation executes against the Color Picker Canvas’s actual pixel Width and Height as, (Color Picker Canvas Width in Pixels) x PointerRingPositionXUnits and (Color Picker Canvas Height in Pixels) x PointerRingPositionYUnits
Up on invoke of the PropertyChanged on those Properties, we make a call to the following SetPointerRingPosition() with the new X and Y position units requested from User.

...
    private void SetPointerRingPosition
                      (double xPositionUnits, double yPositionUnits)
    {
        // Calculate actual X Position
        var xPosition = SkCanvasView.CanvasSize.Width
                                 * xPositionUnits; 
        // Calculate actual Y Position
        var yPosition = SkCanvasView.CanvasSize.Height
                                 * yPositionUnits; 

        // Update as last touch Position on Canvas
        _lastTouchPoint = new SKPoint(Convert.ToSingle(xPosition), Convert.ToSingle(yPosition));
        SkCanvasView.InvalidateSurface();
    }
...

We’re calculating the actual X and Y coordinates against the Canvas pixel size and setting up the _lastTouchPoint with those values, for keeping the Pointer Ring position on canvas in sync with touch inputs positioning and programmatical positioning, then at the end we fire up the SkiaSharp rendering cycle with SkCanvasView.InvalidateSurface();

Handling Pointer Ring Position on Initialization!

We need to handle the positioning of the Pointer Ring on the initialisation or on the rendering of the element during run time. We can achieve this by a one-time execution with a boolean flag, that executes this logic. So upon the first SkiaSharp canvas rendering cycle, we hook up to the PointerRingPositionXUnits and PointerRingPositionYUnits properties and render the Pointer Ring Position to the set value.

...    
    private bool _checkPointerInitPositionDone = false;

...
    private void SkCanvasView_OnPaintSurface
                   (object sender, SKPaintSurfaceEventArgs  e)
    {
        ...
          
        if (!_checkPointerInitPositionDone)
        {
            var x = ((float)skCanvasWidth * (float)PointerRingPositionXUnits);
            var y = ((float)skCanvasHeight * (float)PointerRingPositionYUnits);

            _lastTouchPoint = new SKPoint(x, y);

            _checkPointerInitPositionDone = true;
        }
    }
...

We use _lastTouchPoint variable which is used by the drawing functions for rendering the Pointer Ring on Color Picker’s Canvas.

How to use?

You can easily use this feature in XAML, by accessing ColorPicker.PointerRingPositionXUnits property and ColorPicker.PointerRingPositionYUnits setting the values against your Color Picker’s Width and Height.

<xfColorPickerControl:ColorPicker
    x:Name="ColorPicker"
    PointerRingPositionXUnits="0.3"
    PointerRingPositionYUnits="0.7"
    ...    >
</xfColorPickerControl:ColorPicker>

If you prefer in C# code…

ColorPicker.PointerRingPositionXUnits = 0.3;
ColorPicker.PointerRingPositionYUnits = 0.7;

Here’s some action…

UWP Bug Fix!

One issue I noticed was on UWP run time, where the SkiaSharp’s Canvas touch event behaves differently than iOS and Android. The touch event would get activated even if you hover over the canvas using your mouse pointer, and this was causing the PickedColor property to fire up.
The Touch event should occur only if you actually click on the canvas and drag and drop on the Canvas, so in order to fix this I used the InContact property SKTouchEventArgs inside the touch event to validate on UWP run time.

...
    private void SkCanvasView_OnTouch
                (object sender, SKTouchEventArgs e)
    {
        // to fix the UWP touch behavior
        if (Device.RuntimePlatform == Device.UWP)
        {
            // avoid mouse over touch events
            if (!e.InContact)
                return;
        }

        _lastTouchPoint = e.Location;
        
        ...
    }
...

This fixed the bug on UWP, making sure the touch event is validated before executing the rest of the logic.

Nugetizing!

Alright then, its time to set up our beautiful Color Picker Control for Xamarin.Forms as a Nuget Package using Visual Studio. I’m going first set the Nuget package properties first, then build the package, and finally publish it to Nuget, allowing it to be shared with everyone out there! 😀

Set up package properties…

You could do this straight from Visual Studio Project Properties, or directly from a Nuspec file added to the project itself. For now I would prefer setting up properties in VS Project -> Properties – Package tab, making sure to add all the necessary properties and information about the package as shown below…

Make sure to click on “Generate Nuget package on build” tick, which will enable all the property fields. You could also do this by editing .csproj file of the package project as well, if you require any fine tuned editing…

Now we’re ready to build the package of our Udara.Plugin.XFColorPicker library.

Building the Package…

We need to create the Publish Profile for the package.
Right click on Library project node -> Publish

If this was your first time, it will navigate you to create new Publish Profile tab as shown below…

It is easier to set up a Publish Profile, since you don’t have to manually change your build configuration to Release and then launch a build. Therefore I have set it up now, and next time I publish it will straightaway handle all the configuration for you! 😀

Click Publish, and it nicely builds…

Once we navigate to the folder location mentioned in the above build output…

There we have our nupkg package file, which we can then use to directly upload to Nuget!

Upload to Nuget…

Grab that nupkg file and drag and drop into the upload page of nuget.org and you’re done!

Here you’ll be able to add a short marked down documentation for the users, I would highly recommend you do that since it will increase the support and visibility.

Well that’s all it takes, and the package will be available in a few hours on Nuget!

Updating Package…

Now how do we update our package? if you have noticed around nuget, there’s no update option in in the page where you manage the package. You can update your package by using the NuGet command-line utility or directly uploading an increment build, in which I have opted for the end option to keep it easy.

So when you want to push an update to your package, make sure to update the package properties in Visual Studio to reflect the next immediate version, as shown below where I’m updating from version 1.0.2 to version 1.0.3…

Also do no forget the assembly versioning as well…

Now build your package and directly go to nuget upload page, drag and drop the file…

Make sure to add the nuget documentation and Submit!

Done and dusted, just like that, the updating is done! 😀

Published on nuget:
nuget.org/Udara.Plugin.XFColorPickerControl/

Now anyone can use my Color Picker Control for Xamarin.Forms by setting up this nuget package in their project…

Demoing it up!

As you saw at the beginning I have attached a Demo project into the same parent Solution of Udara.Plugin.XFColorPickerControl, which I have used for testing during development, and to maintain as a demonstration of all the awesome features this plugin provides! 😉

Since this plugin is meant to be compatible on a cross platform environment its impeccable do continuous testing on all the platforms. Anyhow here’s a sneak peek of the demo app…

I have created separate pages to demonstrate awesomeness of each special feature…

BaseColorList Demo:

Android, UWP and iOS…

ColorFlowDirection Demo:

Android, UWP and iOS…

ColorSpectrumStyle Demo:

Android, UWP and iOS…

PointerRingStyling Demo:

Android, UWP and iOS…

Since it’s a pure Xamarin.Forms and can be deployed directly to all three platforms, Android, iOS and Windows UWP, you can do the same with my plugin. Feel free to take a look at the demo app in case if you need trouble shooting.

Conclusion!

There you have it my Color Picker Control for Xamarin.Forms, now published to nuget as a package, with a whole bunch of awesome features, and anyone can easily use it in their own Xamarin.Forms projects! 😀 Pheww… What a joy! Sharing something you’ve been working so hard for a long time. So feel free to give a try, contribute, and any feedback is always welcome…

hosted on github:
github.com/UdaraAlwis/XFColorPickerControl

published on nuget:
nuget.org/Udara.Plugin.XFColorPickerControl/

Well that was fun! So keep in mind I’m going to be implementing more and more features for this plugin in future, and might end up changing some of those features or implementations as well. This blog post will not be constantly updated against them, so many sure to keep in touch with the docs in the github repo itself for future references.

Imagination is the limit yol! 😉

Share the love! 😀 Cheers!

I built an Interactive Color Picker Control for Xamarin.Forms!

Let me share my adventure of building an awesome interactive and responsive Color Picker UI Control for Xamarin.Forms with the help of a little SkiaSharp magic! 😉

To blow your mind, imagine something similar to the Color Picker your have in Ms Paint, HTML Web Color Picker or Google Search Web Color Picker…

Think of how interactive and fun to use those UI Elements are, with their drag and drop pointers on the color spectrum which picks up the color from wherever you drop it.

Why can’t we have the same easy to use fun interactive experience in our Xamarin.Forms apps?

Color Picker control is something that’s missing out of the box in Xamarin.Forms, even when it comes to 3rd party controls out there, neither of them are interactive or responsive, let along any fun to use all. lol 😀

Backstory…

Some time back, I ventured in a project where it required me to build a Color Picking UI element, where it would be easy to use for the user to have a similar experience to what we have with Ms Paint, or Web Color Picker UI elements. So I started off by looking at existing 3rd party library controls out there, which ended up me being disappointed seeing all the controls are just static boring color selection lists of grid style elements.

So I started building my own interactive fun-to-use Color Picker from scratch modeled after the Color Picker UI controls we have in Ms Paint, HTML Web Color Picker, etc… The awesomeness of this would allow you to touch, swipe and pan across a beautiful spectrum of color scheme and pick the color you desire! 😀

So… What?

So what we really need to build in this case is, create a Canvas with a full Color spectrum similar to a rainbow gradient effect spreading across, while allowing the User to touch at any given pixel point, up on which an event will trigger capturing the Color value of that pixel point. Also we should be able to highlight that touch triggered pixel point, giving the feedback to the User.

How? in a Gist…

Frankly this is not possible at all, out of the box in Xamarin.Forms, but with the help of a little SkiaSharp magic, this would be possible! SkiaSharp is the awesome 2D graphics rendering library that let’s you do all kinds of cool stuff on top of Xamarin.Forms. So basically we’re going to draw the full Color spectrum with a rainbow-gradient style spreading across a 2D canvas with the help of SkiaSharp.

We will define the list of main colors we need to include across the Canvas, while defining the Gradient fading effect between them. Then with regards to Touch, we need to enable this on the SkiaSharp canvas, and subscribe to the touch handling events.

Then given the User triggers a touch even on the Canvas, we will pick up those coordinate values on the canvas, and pick the Color values of the Pixel at that point on the Canvas. Voiala! We got the Color value picked by the User! 😉 Then as a responsive feedback we will draw highlighting circle around that pixel point coordinates on the Canvas. 😀

Well there you have it, quite straight forward eh! 😉

Sneak Peak!

Just to give a little sneak peak, here’s what I build… 😀 Behold the Interactive Color Picker Control for Xamarin.Forms!

Pretty awesome eh! Xamarin.Forms + SkiaSharp magic! 😉

Project hosted on github:  
https://github.com/UdaraAlwis/XFColorPickerControl 

Alright then let me show you how I built it…

Let’s start building!

Let’s begin by adding SkiaSharp to our Xamarin.Forms project. Open up Nuget Package Manager on your Xamarin.Forms solution node and add SkiaSharp.View.Forms Nuget to your .NET Standard project node and platform nodes as shown below…

That’s it, no extra set up is needed… 😉

Next we need to create our Custom Control, which I’m going to name as ColorPickerControl!

The ColorPickerControl!

It’s better to keep this in a dedicated folder in the .NET Standard project, inside a “Controls” folder, for the sake of clarity! 😉 So let’s create our ColorPickerControl as a type ContentView XAML element in the Controls folder…

<?xml version="1.0" encoding="utf-8" ?>
<ContentView
    x:Class="XFColorPickerControl.Controls.ColorPickerControl"
    xmlns="http://xamarin.com/schemas/2014/forms"
    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
    xmlns:d="http://xamarin.com/schemas/2014/forms/design"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d">

    <!-- Content of the Control -->

</ContentView>

Then as of the code behind, let’s set up a PickedColor Property that holds the value of the Color that User picks during the run time, and an event that fires itself up on that action, PickedColorChanged event!

[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class ColorPickerControl : ContentView
{
	public event EventHandler<Color> PickedColorChanged;

	public static readonly BindableProperty PickedColorProperty
		= BindableProperty.Create(
			nameof(PickedColor),
			typeof(Color),
			typeof(ColorPickerControl));

	public Color PickedColor
	{
		get { return (Color)GetValue(PickedColorProperty); }
		set { SetValue(PickedColorProperty, value); }
	}

	public ColorPickerControl()
	{
		InitializeComponent();
	}
}

Alright next on to setting up the SkiaSharp bits in our Control…

The SkiaSharp magic!

SkiaSharp’s magical Canvas called SKCanvasView is what we’re going to use to Draw our Rainbow Color Spectrum and handle all the Touch event bits… So let’s begin by adding the SKCanvasView to our ColorPickerControl XAML and also the SkiaSharp.Views.Forms reference in the XAML itself..

<ContentView
    ...
    xmlns:skia="clr-namespace:SkiaSharp.Views.Forms;assembly=SkiaSharp.Views.Forms"
	...
	>

    <skia:SKCanvasView
        x:Name="SkCanvasView"
        EnableTouchEvents="True"
        PaintSurface="SkCanvasView_OnPaintSurface"
        Touch="SkCanvasView_OnTouch" />

</ContentView>

Code on Github: /XFColorPickerControl/Controls/ColorPickerControl.xaml

As you can see on my SKCanvasView element, I have enabled touch events with EnableTouchEvents property and subscribed to Touch event with SkCanvasView_OnTouch. Subscribing to PaintSurface allows us to draw full blown 2D graphics on the Canvas, which is why we have created the event SkCanvasView_OnPaintSurface event.

So let’s handle all those events in the code behind of our ColorPickerControl…

[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class ColorPickerControl : ContentView
{
	...
	
	private void SkCanvasView_OnPaintSurface
                      (object sender, SKPaintSurfaceEventArgs e)
	{
		var skImageInfo = e.Info;
		var skSurface = e.Surface;
		var skCanvas = skSurface.Canvas;

		var skCanvasWidth = skImageInfo.Width;
		var skCanvasHeight = skImageInfo.Height;

		skCanvas.Clear(SKColors.White);

		...
	}
	
	private void SkCanvasView_OnTouch
                      (object sender, SKTouchEventArgs e)
	{
		...
	}
}

Code on Github: /XFColorPickerControl/Controls/ColorPickerControl.xaml.cs

So we’re setting up the basic values we need to use inside SkCanvasView_OnPaintSurface with the skImageInfo, skSurface, skCanvas, which will be very useful in our next set of code snippets!

This is where our core implementation is going to be taking place, let me get into details of each code snippet one by one, but you can always go back to the full code on github and take a look by yourself… 😉 Let’s continue…

The Touch!

Let me begin diving in with the SkCanvasView_OnTouch event method implementation, which handles the touch events occurs on the SkiaSharp Canvas we added into our Control.

We need to keep a track on each Touch event that occurs, so we will store that in a local variable _lastTouchPoint which is of type SKPoint. Since we need to only consider the touch events that occur inside the canvas region, we’re validating each touch coordinate (X,Y) that comes into the event.

...
	private void SkCanvasView_OnTouch
	               (object sender, SKTouchEventArgs e)
	{
		_lastTouchPoint = e.Location;

		var canvasSize = SkCanvasView.CanvasSize;

		// Check for each touch point XY position to be inside Canvas
		// Ignore any Touch event ocurred outside the Canvas region 
		if ((e.Location.X > 0 && e.Location.X < canvasSize.Width) &&
			(e.Location.Y > 0 && e.Location.Y < canvasSize.Height))
		{
			e.Handled = true;

			// update the Canvas as you wish
			SkCanvasView.InvalidateSurface();
		}
	}
...

Based on the validated touch event coordinate, we’re firing up the SkiaSharp Canvas drawing cycle, SkCanvasView.InvalidateSurface(), where we will handle, picking up the color on the touch point and redrawing the canvas to highlight the touch point coordinates on the Canvas.

The Rainbow Color Spectrum!

So this right here is the most critical functionality that we need to implement, drawing the beautiful rainbow gradient color spectrum on our SkiaSharp Canvas. We’re going to draw the following list of colors across the spectrum, which values I picked up with the help of Google Web Color Picker..

Red | Yellow | Green (Lime) | Aqua | Blue | Fuchsia | Red
undefined

This will take place in our SkCanvasView_OnPaintSurface event method that we created in the previous step, where we create the Paint object that’s going to draw the color spectrum on the Canvas, along with the gradient fading effect between all the colors using SKShader object.

...
	private void SkCanvasView_OnPaintSurface
	               (object sender, SKPaintSurfaceEventArgs  e)
	{
		// Draw gradient rainbow Color spectrum
		using (var paint = new SKPaint())
		{
			paint.IsAntialias = true;

			// Initiate the primary Color list
			// picked up from Google Web Color Picker
			var colors = new SKColor[]
			{
				new SKColor(255, 0, 0), // Red
				new SKColor(255, 255, 0), // Yellow
				new SKColor(0, 255, 0), // Green (Lime)
				new SKColor(0, 255, 255), // Aqua
				new SKColor(0, 0, 255), // Blue
				new SKColor(255, 0, 255), // Fuchsia
				new SKColor(255, 0, 0), // Red
			};

			// create the gradient shader between Colors
			using (var shader = SKShader.CreateLinearGradient(
				new SKPoint(0, 0),
				new SKPoint(skCanvasWidth, 0),
				colors,
				null,
				SKShaderTileMode.Clamp))
			{
				paint.Shader = shader;
				skCanvas.DrawPaint(paint);
			}
		}
	}
...

As you can see we are defining the list of Colors with SKColor objects, that’ll populate the rainbow color spectrum on our Canvas. Then we use SKShader.CreateLinearGradient() method to build the gradient shader using the list of colors, and then we draw it on the Canvas using skCanvas.DrawPaint().

Keep a note how SKPoint() objects define the starting and ending coordinates on the Canvas which the shader will spread through, thus we’re taking skCanvasWidth picking the corner most value on the X axis. 😉

The Darker Gradient Strip!

Next we need to draw the darker shadow gradient strip on the Canvas allowing Users to pick the Darker Colors of the primary colors we defined.

We’re going to paint the darker color regions by drawing another layer on top of the previous drawn layer creating the illusion of darker regions of each color.

This will take place in our SkCanvasView_OnPaintSurface but below the code snippet that I showed before. Very much similar to the previous snippet, we’re doing almost the same thing but adding a darker gradient region at the bottom of the Canvas.

...
	private void SkCanvasView_OnPaintSurface
	               (object sender, SKPaintSurfaceEventArgs  e)
	{
		...
		
		// Draw darker gradient spectrum
		using (var paint = new SKPaint())
		{
			paint.IsAntialias = true;

			// Initiate the darkened primary color list
			var colors = new SKColor[]
			{
				SKColors.Transparent,
				SKColors.Black
			};

			// create the gradient shader 
			using (var shader = SKShader.CreateLinearGradient(
				new SKPoint(0, 0),
				new SKPoint(0, skCanvasHeight),
				colors,
				null,
				SKShaderTileMode.Clamp))
			{
				paint.Shader = shader;
				skCanvas.DrawPaint(paint);
			}
		}
	}
...

Here we’re drawing the darkening gradient layer starting from Transparent color to Black color across the Y axis, thus we’re taking skCanvasHeight picking the corner most value on the Y axis similar to what we did before. 😉

Here they are side by side, before and after drawing darker gradient strip… 😀

The Lighter Gradient Strip!?

This this is bit of an extra cherry on top, as you may have seen some of those Color Pickers include picking Lighter versions of the Colors. We can easily do this by adding a White color object to the list of colors in the code snippet I shared above.

...         
	...
		 ...
			// Initiate the darkened primary color list
			var colors = new SKColor[]
			{
				SKColors.White,
				SKColors.Transparent,
				SKColors.Black
			};  
		 ...
	...
...	

This will draw the secondary layer with White | Transparent | Black gradient effects on top of the full color spectrum layer.

There you go, with the Lighter color gradient strip. Although I wouldn’t include this in my demo app code 😛 Just coz I don’t like it! lol

Picking the Color on Touch!

This is the most crucial bit of this Control, also the most time consuming implementation I had to go through during my trial and error experimentation to get this working! 😮

We are going to be using the _lastTouchPoint SKPoint object, that we created before, in order to access the coordinate data of the touch point on Canvas. Then we look for extract the pixel color values on that coordinate on the Canvas, given that the Canvas is already rendered with the Color spectrum.

This will take place in our SkCanvasView_OnPaintSurface event method, below the color spectrum drawing code snippet.

Experimentation Phase…

Picking a pixel on the rendered Canvas layer is not a straight forward task, the idea here is to capture a quick snapshot of the Canvas graphic layer and convert that into a bitmap image, and use that image to pick the pixels from using the touch coordinates.

As you can see from below, the first implementation I put together which captures a snapshot of the Canvas surface layer and load it into a SKBitmap image, then I retrieve the Pixel data on that image using bitmap.GetPixel() by passing in the touch point values.

...
	private void SkCanvasView_OnPaintSurface
				   (object sender, SKPaintSurfaceEventArgs  e)
	{
		...
		
		// Picking the Pixel Color values on the Touch Point

		// Represent the color of the current Touch point
		SKColor touchPointColor;

		//// Inefficient: causes memory overload errors
		//using (var skImage = skSurface.Snapshot())
		//{
		//	using (var skData = skImage.Encode(SKEncodedImageFormat.Webp, 100))
		//	{
		//		if (skData != null)
		//		{
		//			using (SKBitmap bitmap = SKBitmap.Decode(skData))
		//			{
		//				touchPointColor = bitmap.GetPixel(
		//									(int)_lastTouchPoint.X, (int)_lastTouchPoint.Y);
		//			}
		//		}
		//	}
		//}
		
		...
	}
...

Later it started causing performance issues due to calling Snapshot() method during each rendering cycle, which is a very heavy process, and even sometimes overloads the memory.

Better Solution…

So after a bit more exploration with trial and error, I managed to build a solution based on a Xamarin Forum response that I found to a similar requirement I had…
https://forums.xamarin.com/discussion/92899/read-a-pixel-info-from-a-canvas

What if instead of taking a snapshot, we use SKImageInfo object of the Canvas instance and extract a SKBitmap image and read the pixel color data of the touch point coordinates. This is way more efficient and consumes much less memory for execution… 😉

...
	private void SkCanvasView_OnPaintSurface
				   (object sender, SKPaintSurfaceEventArgs  e)
	{
		...
		
		// Picking the Pixel Color values on the Touch Point

		// Represent the color of the current Touch point
		SKColor touchPointColor;

		// Efficient and fast
		// https://forums.xamarin.com/discussion/92899/read-a-pixel-info-from-a-canvas
		// create the 1x1 bitmap (auto allocates the pixel buffer)
		using (SKBitmap bitmap = new SKBitmap(skImageInfo))
		{
			// get the pixel buffer for the bitmap
			IntPtr dstpixels = bitmap.GetPixels();

			// read the surface into the bitmap
			skSurface.ReadPixels(skImageInfo,
				dstpixels,
				skImageInfo.RowBytes,
				(int)_lastTouchPoint.X, (int)_lastTouchPoint.Y);

			// access the color
			touchPointColor = bitmap.GetPixel(0, 0);
		}
		
		...
	}
...

As you can see we’re using skSurface.ReadPixels() to load the pixel data on the coordinates, and finally loading the exact pixel data into touchPointColor as a SKColor object type. 😀

So now we picked the Color from a given touch point on the Canvas, let’s move to the next bit…

The Touch Feedback!

This is the part where we provide on touch feedback for the User by highlighting the touch point on the Canvas up on each touch event. As you noticed we’re firing up the OnPaintSurface event upon each touch event of the Canvas, hence we can draw the highlighting region on the Canvas right here as a feedback loop.

We’re simply going to create a SKPaint object, with White color and use skCanvas.DrawCircle() to draw a circle around the touch point coordinates on the Canvas. Then as an added extra, I’m drawing another circle on top of it with the picked color, so that we can emphasize on the pixel color of the touch point. 😉

...
	private void SkCanvasView_OnPaintSurface
				   (object sender, SKPaintSurfaceEventArgs  e)
	{
		...
		
		// Painting the Touch point
		using (SKPaint paintTouchPoint = new SKPaint())
		{
			paintTouchPoint.Style = SKPaintStyle.Fill;
			paintTouchPoint.Color = SKColors.White;
			paintTouchPoint.IsAntialias = true;

			// Outer circle (Ring)
			var outerRingRadius = 
				((float)skCanvasWidth/
                    (float)skCanvasHeight) * (float)18;
			skCanvas.DrawCircle(
				_lastTouchPoint.X,
				_lastTouchPoint.Y,
				outerRingRadius, paintTouchPoint);

			// Draw another circle with picked color
			paintTouchPoint.Color = touchPointColor;

			// Outer circle (Ring)
			var innerRingRadius = 
				((float)skCanvasWidth/
                    (float)skCanvasHeight) * (float)12;
			skCanvas.DrawCircle(
				_lastTouchPoint.X,
				_lastTouchPoint.Y,
				innerRingRadius, paintTouchPoint);
		}
		
		...
	}
...

As you can see _lastTouchPoint X and Y coordinates to draw the circle, and we’re calculating the radius value for both circles by adjacent to Canvas width and height, so it renders nicely on any device scale.

And then to the final step, returning back the Color that we Picked from our ColorPickerControl!

Return the Picked Color!

Now we need to return back the Color value that the User picked, to the subscribers or whoever’s listening to the PickedColor property and PickedColorChanged event.

...
	private void SkCanvasView_OnPaintSurface
				   (object sender, SKPaintSurfaceEventArgs  e)
	{
		...
		
		// Set selected color
		PickedColor = touchPointColor.ToFormsColor();
		PickedColorChanged?.Invoke(this, PickedColor);
		
		...
	}
...

It’s as simple as setting the Value and firing up the Event with the new Color value parameter…

Alright, that’s it! We’ve finished building our awesome ColorPickerControl! 😀

Let’s try it out!

Since we created it as a standalone UI Control you can use this little awesomeness anywhere in your Xamarin.Forms project as you would with any UI element as easy as below…

<controls:ColorPickerControl 
	x:Name="ColorPicker"
	PickedColorChanged="ColorPicker_PickedColorChanged" />

So let’s try adding this to a ContentPage with a nice little Frame element around it with a fixed Height and Width…

<Frame
	x:Name="ColorPickerFrame"
	CornerRadius="8"
	HeightRequest="200"
	HorizontalOptions="Center"
	WidthRequest="350">
	<controls:ColorPickerControl 
		x:Name="ColorPicker"
		PickedColorChanged="ColorPicker_PickedColorChanged" />
</Frame>

This will give a nice little frame around the Color picker control, then on to the code behind…

private void ColorPicker_PickedColorChanged
			(object sender, Color colorPicked)
{
	ColorPickerHolderFrame.BackgroundColor = colorPicked;
}

PickedColorChanged provide you the picked Color value, so you can do what you wish with it!

Fire it up!

Time to fire it up yo! 😀 I’ve prepared a little demo app with my awesome ColorPickerControl for Xamarin.Forms, deployed for Android, iOS and UWP…

Android, iOS and UWP side by side working like a charm! 😀

Project hosted on github:  
https://github.com/UdaraAlwis/XFColorPickerControl 

The possibilities are endless, just a matter of your own creativity! 😉

Conclusion…

An interactive and responsive Color Picker is something that’s missing from Xamarin.Forms out of the box, even when it comes existing to 3rd party controls, there’s no such that fills the requirement, similar to MS Paint Color Picker, or HTML Web Color Pickers.

You can do all kinds of cool interactive 2D graphics rendering stuff with SkiaSharp on Xamarin.Forms, and thanks this, I managed to build a full fledged interactive and fun-to-use Color Picker UI Control, which is lacking in Xamarin.Forms ecosystem right now.

I’m planning to release a nuget package with this control quite soon, with a whole bunch of extra cool features embedded in 😉 So keep in touch!

Imagination is the limit yol! 😉

Share the love! 😀 Cheers!

Pushing the limits of Hybrid WebView in Xamarin.Forms!

Let’s push the possible limits of Hybrid WebView and build something awesome in Xamarin.Forms! 😀

Remember my last blog post, Building a bi-directional interop bridge with WebView in Xamarin.Forms! which is where I shared about building a bi-directional invoke bridge between Javascript and C# dotnet run time using Hybrid WebView.

So based on that I went on a little journey to push the limits of this Hybrid WebView and built some cool demos with it. So here I am sharing it all with yol! 😉

Pushing the limits!

BTW: This is going to be a continuation of my previous blog post, so better take a look at it first if you haven’t: Building a bi-directional interop bridge with WebView in Xamarin.Forms!

To put it into fancy words,

We built a bi-directional communication bridge, between completely different run times, with possibility of two way execution invoke on demand! Hybrid WebView…

So now, the question is, what can we do to push the limits of our Hybrid WebView? Sounds like something for the imagination to limit!

Behold the awesomeness!

Imagine, being able to load a Web page into you Xamarin.Forms WebView, and being able to access Device features such as Camera, GPS Location, Accelerometer, etc..

Basically we’re going access Device Native features through the WebView and retrieve data directly from C# .NET run time in our Xamarin.Forms app! You will be able to load any HTML content, either from a Web Hosted source or locally generated HTML source, it would work like a charm thanks to the Hybrid WebView!

In order to demonstrate this awesomeness, let’s try out the following feature for the demo implementation…

  • Capture Photos using Device Camera
  • Pick Photos from Device Gallery
  • Get Device Native information
  • Get Device GPS Location data

All those device features and data will be accessed from the Javascript running inside the Hybrid WebView! 😉

Like I mentioned before, we will have two HTML sources for this demo, a web hosted HTML source and a locally generated HTML source to make sure it works for either cases! 😀

Now here’s a bit about what will help us build this awesome demo..

– Bi directional bridge!
Being able to invoke executions directly between the Javascript environment and C# .NET Xamarin.Forms run time, is what is going to help us build this awesomeness!

Javascript <~> Xamarin.Forms (C# .NET)

So you can pass data from the Javascript that’s running inside the Hybrid WebView out into the C# .NET run time, as well as you can pass data directly into the Javascript that’s running inside the Hybrid WebView.

– Multiple parameters…
In my previous blog post I mentioned this at the end where you can extend the same implementation we did for our Hybrid WebView, into supporting multiple parameters, so here I will use this to demonstrate what we’re going to build!

Sneak Peak!

Now here’s some action on the go with this awesomeness… 😉

As usual I’ve hosted this whole demo project up on my github repo:

Code on github: https://github.com/UdaraAlwis/XFHybridWebViewAdvDemo

This is how we do it!

So let’s get right into it, but first let’s make sure some prerequisites.

– Basic Hybrid WebView implementation
Refer to my previous post and check out the implementation of the Hybrid WebView. Building a bi-directional interop bridge with WebView in Xamarin.Forms!

– Xamarin.Essentials set up to access the device native feature
You need to implement Xamarin.Essentials and set up all the device native features and their configuration for the features you wish to use. https://docs.microsoft.com/en-us/xamarin/essentials/

Multiple Parameters support!

Let’s begin with adding support for multiple parameters in our Hybrid WebView as follows…

public class HybridWebView : WebView
{
	private Action<string, string> _action;

	public void RegisterAction(Action<string, string> callback)
	{
		_action = callback;
	}

	public void Cleanup()
	{
		_action = null;
	}

	public void InvokeAction(string param1, string param2)
	{
		if (_action == null || (param1 == null && param2 == null))
		{
			return;
		}

		if (MainThread.IsMainThread)
			_action.Invoke(param1, param2);
		else
			MainThread.BeginInvokeOnMainThread(() => _action.Invoke(param1, param2));
	}
}

Code on github: /XFHybridWebViewAdvDemo/Controls/HybridWebView.cs

As you can see, I have defined Action property with two parameters, along side the setter method of it, RegisterAction() accepts Action instances with two parameters.

InvokeAction() which gets called from each native renderer level now accepts two parameters accordingly. As an addition I have added an enforced UI Thread execution using Xamarin.Essentials.MainThread feature, since we’re going to access IO heavy device features.

Following the same pattern you can add as many number of parameters as you wish! 😉

We need to add support for this in our Javascript implementation as well, so we create a pre defined separator (a pipe separator preferably “|”) that separates parameters in the data object we’re sending from javascript to Hybrid WebView’s Renderer’s script handler.

..
invokexamarinforms('PHOTO|CAMERA')
..

When our Hybrid WebView renderers receive the invoke from Javascript, we need to handle the incoming data object as follows by splitting it up using the separator we defined…

var dataBody = data;
if (dataBody.Contains("|"))
{
	var paramArray = dataBody.Split("|");
	var param1 = paramArray[0];
	var param2 = paramArray[1];
	((HybridWebView)hybridRenderer.Element).InvokeAction(param1, param2);
}
else
{
	((HybridWebView)hybridRenderer.Element).InvokeAction(dataBody, null);
}

Then we pass it on to the InvokeAction() event, for Xamarin.Forms level to handle whichever the Action has subscribed to it. This way you can handle as many parameters as you wish!

Launch invoke from HTML Javascript to C# .NET!

So here’s how we set up the simple implementation to call up the invokeXamarinFormsAction() method that we have defined in our Hybrid WebView platform Renderers. Well there’s not much different from what we implemented in my previous demo, but here we are passing multiple parameters into the javascript method upon the button click.

...

<script>
...
function invokexamarinforms(param){
    try{
        invokeXamarinFormsAction(param);
    }
    catch(err){
        alert(err);
    }
}
</script>

...

<button type="button" 
	onclick="invokexamarinforms('PHOTO|CAMERA')">
	Get from Xamarin.Forms</button>

...

This is something I’ve explained step by step in my previous blog post so I wouldn’t go into details in here. You can define as many onclick actions as you wish with the set of predefined parameters like “PHOTO|CAMERA” and “PHOTO|GALLERY”, even single parameters, “GPS” and “DEVICEINFO”, etc…

Next you need to handle those parameters in C# code to execute the specific action we’re targeting, as simple as a if-else block as follows, or even a switch statement would suffice.

...

private async void ExecuteActionFromJavascript(string param1, string param2)
{
	...	
	if (param1 != null && param1.Equals("PHOTO") && param2.Equals("CAMERA"))
	{
		var result = await _deviceFeaturesHelper.TakePhoto(this);
		if (result != null)
		{
			...
		}
	}
        ...
	else if (param1 != null && param1.Equals("DEVICEINFO"))
	{
		var result = await _deviceFeaturesHelper.GetDeviceData();
		if (result != null)
		{
			...
		}
	}	
	...
}

Based on the requested action we execute it in C#, in this case accessing Camera and Capturing a photo _deviceFeaturesHelper.TakePhoto() or even getting Device Native information _deviceFeaturesHelper.GetDeviceData() as shown above.

Let’s move to the next step of this chain…

Ping back from C# .NET to HTML Javascript!?

Now that we established pathway to call the C# .NET run time from Javascript, we’re able to invoke any action, but how do we get back the result data into the Javascript?

So in my previous blog article Talking to your WebView in Xamarin.Forms! which explains how easy it is to pass data into the Javascript rendered inside the WebView at run time, since our Hybrid WebView is an extension of the default WebView, we can use the same method here…

...
        var result = await _deviceFeaturesHelper.GetDeviceData();
        if (result != null)
        {
             await webViewElement
                   .EvaluateJavaScriptAsync($"setresult('{result}')");
        }
...

So we’re calling up on EvaluateJavaScriptAsync() with the Javascript function name that’s accepting to the results for this specific action. This function needs to be created inside the Javascript before hand, that is rendered inside the Hybrid WebView as follows…

...
<script>
...
	function setresult(value) {
		// - display the value in HTML
		// - send the data to server
	}
</script>
...

Once the data is passed into your Javascript function, You can do whaever you want with the data, be it display in the HTML, or send it up to a web server, your choice! 😉

Calling the Device Native!

Well this is quite simple if you know how to use Xamarin.Essentials to access device native features and other 3rd party plugins to access various features from Xamarin.Forms! But I’ll quickly walk through the code that I’m using in this demo.

I’ve basically created like a little Facade layer which handles all the device native features required as follows, and each method handles a given specific feature such as Camera and GPS features using their respective services of plugin calls…

public class DeviceFeaturesHelper
{
	public async Task<string> TakePhoto(ContentPage pageContext)
	{
		// launch Media Plugin to capture photos from camera
	
		...

		return imageAsBase64String;
	}
	
	public async Task<string> GetDeviceData() 
	{
		// launch Xamarin.Essentials to load device info

		return $"{nameof(DeviceInfo.Model)}: {device}<br />" +
			$"{nameof(DeviceInfo.Manufacturer)}: {manufacturer}<br />" + 
			$"{nameof(DeviceInfo.Name)}: {deviceName}<br />";
	}
}

Code on github: /XFHybridWebViewAdvDemo/DeviceFeaturesHelper.cs

So what you need to keep in mind is that we need to return a value that’s compatible to be displayed inside our WebView, based on HTML, that’s why you see I have modified some of those returned values accordingly, such as Image objects are returned as base64 strings and device information formatted as a text block with <br /> inline.

These methods are called from the Hybrid WebView’s Invoke action that we created before and results are returned to be pushed back into Javascript.

Handling Media Image objects…

Using Media Plugin for Xamarin.Forms, provides you with a MediaFile object which contains the Image object that you acquired either from Camera or Gallery, but how do we convert that into something that’s compatible to be pushed into Javascript-HTML environment?

The solution is,

MediaFile -> byte[] array -> Base64 string

We’re going to convert our MediaFile object into a byte[] array, then convert again into a base64 string, which makes it so much easier to transfer the data into the javascript run time and use that object for any purposes inside javascript itself. Here’s my code snippet for this…

public async Task<string> TakePhoto(ContentPage pageContext)
{
        ...
	var file = await CrossMedia.Current.TakePhotoAsync(...);

	// Convert bytes to base64 content
	var imageAsBase64String = Convert.ToBase64String(ConvertFileToByteArray(file));

	return imageAsBase64String;
}

private byte[] ConvertFileToByteArray(MediaFile imageFile)
{
	// Convert Image to bytes
	byte[] imageAsBytes;
	using (var memoryStream = new MemoryStream())
	{
		imageFile.GetStream().CopyTo(memoryStream);
		imageFile.Dispose();
		imageAsBytes = memoryStream.ToArray();
	}

	return imageAsBytes;
}

This is what you saw in the previous section which I have used in my /DeviceFeaturesHelper.cs
You can use this in the javascript functions as easy as below,

function setresult_takephoto(value) 
{
	document.getElementById("photoCamera_ResultElement").src 
                                             = "data:image/png;base64," + value;
}

Well that’s the entire set up of this awesome demo, so then let’s see it in action…

Fire it up!

Here’s the web page we’re loading: https://testwebpage.htmlsave.com/

Look at em on fire, Android, UWP and iOS side by side…

Code on github: https://github.com/UdaraAlwis/XFHybridWebViewAdvDemo

Conclusion…

This was just me pushing the limits of the Hybrid WebView to build awesome stuff with Xamarin.Forms! This will definitely come in handy whenever you get a scenario you need to implement an existing Web App into a Xamarin.Forms app, and you need to let the user use it as a Mobile App, with being able to access device native features.

Well that concludes it. Hope you find it useful!

Share the love! 😀 Cheers!

The step by step set up of Media Plugin for Xamarin.Forms!

Let’s properly set up Media Plugin (Xam.Plugin.Media) for Xamarin.Forms, harnessing the full capabilities with an optimized implementation! 😀

This is a continuation from my previous blog post, Behold the check-list of Media Plugin set up for Xamarin.Forms! where I shared the list of important bits you need to focus on when setting up the Media Plugin.

So here I’m building up on that and compiling a step by step guide implementation of the Xam.Plugin.Media for Xamarin.Forms, with the latest updates!

Backstory…

During my recent implementation with the Media Plugin for Xamarin.Forms, I realize that there are some new updates to this Plugin and its dependent Permission plugin that are not documented properly out there!

So I thought of writing up a new article with those updated bits and a better implementation with this library in a proper manner to harness the best of its performance and features without running into accidental bugs! 😉

Media Plugin – Xam.Plugin.Media!

Xam.Plugin.Media is the free Plugin Library by James Montemagno, that allows us to easily interact with Capturing Photos and Video and accessing them from the device Galley using Xamarin.Forms! So this library provides two main functionalities,

  • Capture Photos/Videos from Camera
  • Pick Photos/Videos from Gallery

Apart from that it allows you to Crop, Compress Photos, Set Custom Sizing and Quality, Save to Albums, and etc. It fully supports Android, iOS, UWP (Windows), and even Tizen device platforms. Quite an awesome library for sure!

Github: https://github.com/jamesmontemagno/MediaPlugin
Nuget: http://www.nuget.org/packages/Xam.Plugin.Media

This library internally depends itself on Permissions Plugin (Plugin.Permissions) for taking care of the Permissions that are required to handle in each Native platform to access Camera features and device Gallery features.

Step by Step!

Alright then let’s take a step by step walk through of setting up Media Plugin in your Xamarin.Forms project from scratch!

1. Let the set up begin!

Assuming you have already created your Xamarin.Forms project, let’s begin by adding the Xam.Plugin.Media into your Project from Nuget Package Manager.

Lets search for “Xam.Plugin.Media” in Nuget and install the library for all the project nodes in your solution, Xamarin.Forms Host project, Android, iOS, and UWP (Windows) platform nodes.

2. Initialize()!

Then you need to set up the Initialization of the Media Plugin in the Xamarin.Forms layer, by calling up the Initialize() method preferably at the start up of the App.

If you’re using a Service instance to be used with Media Plugin, then you should set this is up in the Constructor of it.

Now let’s set up the configuration for all the platform projects one by one…

Let’s set up Android!

Let’s begin with the Android bits, which is the longest set of configuration.

1. Permissions in AndroidManifest!

by adding the Permission bits that are required for the Media Plugin. Simply go to Android Project -> Properties -> Click on “Android Manifest” tab -> scroll down to “Required Permissions” section…

Simply select those two Permissions, for Reading and Writing data to the device storage, in terms of Capturing Photos and Videos and saving them during run time.

You could even add them manually in the AndroidManifest.xml file.

<?xml version="1.0" encoding="utf-8"?>
<manifest ... >
    <uses-sdk ... />
    <application ... >
    ...
	<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
	<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
    ...
  </application>
    ...
</manifest>

Then again, unless you’re going to saving your captured Photos or Videos then no need to add the “WRITE” permission. So make sure to decide on your requirement.

2. Permission Plugin – OnRequestPermissionsResult()

Next we need to set up the call back for the Permission Plugin on the OnRequestPermissionsResult() method in your MainActivity.cs class.

on github: /XFMediaPluginDemo.Android/MainActivity.cs

Visual Studio 2019 adds the override of this method automatically to your MainActivity class, but if its not there you need to set up as shown above.

3. FileProviderfile_paths.xml

We need to set up the FileProvider path values in the file_paths.xml, so go ahead create a new folder called “xml” in your “Resources” folder, and add a new XML file called “file_paths.xml” with the following content.

on github: /XFMediaPluginDemo.Android/Resources/xml/file_paths.xml

Oh, and make sure the Build Action of that file is set to “AndroidResource” in Properties.

4. FileProvider in AndroidManifest!

Then let’s add the FileProvider definition in the AndroidManifest.xml

on github: /XFMediaPluginDemo.Android/Properties/AndroidManifest.xml

This should be added inside the <application> node.

5. Plugin.CurrentActity set up…

We need to set up the Plugin.CurrentActivity plugin for Media Plugin to attach itself to the active Activity during the run time. Nuget Package Manager -> install Plugin.CurrentActivity, only into your Android project node.

Now that’s installed we need to set it up in the code as well.

6. Plugin.CurrentActity Initialization!

First we need to create the MainApplication.cs class set up that inherits from Android.App.Application base for initializing the CrossCurrentActivity Instance up on the Activity change at run time.

on github: /XFMediaPluginDemo.Android/MainApplication.cs

Next we need to set up the init() call on MainActivity.cs class as well.

on github: /XFMediaPluginDemo.Android/MainActivity.cs

Here also we’re calling the Init() method of CurrentActivity plugin but this time we’re forwarding the Bundle parameter that’s passed into the OnCreate() method.

7. Hardware Requirement filter!?!

Now this is an optional step, once your app is published, and you want to Google Play store to make your app available only for devices that has the following features, “Camera”, “Camera with Auto Focus”, etc, then you need to add the following “UsesFeatures” attributes to your AssemblyInfo.cs file.

That concludes the Android project set up.

Let’s set up iOS!

The iOS set up is much easier actually where we only have to set up the permissions.

1. Permissions in Info.plist!

On your iOS project, right click on the Info.plist file -> Open With -> select XML (Text) Editor option, which will open up in the XML editor window as follows.

on github: /XFMediaPluginDemo.iOS/Info.plist

You need to add Permissions as shown here, with an appropriate description, which will be used to show to the User when the Permissions are being requested at run time. You need to explain what those Permissions are used for in your app.

<plist version="1.0">
<dict>
    ...
    ...
    <key>NSCameraUsageDescription</key>
    <string>This app needs access to the camera to take photos.</string>
    <key>NSPhotoLibraryUsageDescription</key>
    <string>This app needs access to photos.</string>
    <key>NSMicrophoneUsageDescription</key>
    <string>This app needs access to microphone.</string>
    <key>NSPhotoLibraryAddUsageDescription</key>
    <string>This app needs access to the photo gallery.</string>
</dict>
</plist>

But here also I’m reminding, set up only the Permissions that are absolutely required by your app’s functionality.

That concludes the iOS project set up.

Let’s set up UWP!

Well in UWP (Windows) project is even more easier to set up

1. Permissions in Package.appxmanifest!

Simply open up the Package.appxmanifest file in your UWP project -> Go to “Capabilities” tab -> Tick on “Webcam” option from the Capabilities list.

on github: /XFMediaPluginDemo.UWP/Package.appxmanifest

That concludes the UWP project set up.

Let the Xamarin.Forms, coding begin!

Now this is where we’re going to set up our implementation to use the Media Plugin in our Xamarin.Forms project host.

Doesn’t matter whether you’re going to implement in Page code behind or MVVM heavy ViewModel, we should maintain a clean decoupled structure as much as possible.

Pre-requisites!

So each feature we access we need to perform the following,

  • Check for the availability of the feature (ex: Camera, Gallery)

    Media Plugin provides these bool properties which allows you to check for the availability of the features you want to access, such as Camera, and Gallery. If they return true then it is safe to proceed with the call.
...
if (!CrossMedia.Current.IsCameraAvailable ||
		!CrossMedia.Current.IsTakePhotoSupported)
{
	await DisplayAlert("No Camera", 
              "Sorry! No camera available.", "OK");
	return null;
}
...
  • Check for the status of the Permission required (ex: Camera, Storage)

    This is another safety layer that is also recommended, checking the Status of the Permission before you access those features from Media Plugin. Based on it you can perform requesting Permission from the User during run time using the Permission Plugin that’s already set up in your project.
...
var cameraStatus = await CrossPermissions.Current.
			CheckPermissionStatusAsync(Permission.Camera);
var storageStatus = await CrossPermissions.Current.
			CheckPermissionStatusAsync(Permission.Storage);
var photosStatus = await CrossPermissions.Current.
			CheckPermissionStatusAsync(Permission.Photos);
...

Those two check ups are recommended as safety layers for smooth experience for the user and to avoid running into unexpected issues. Once those two calls are satisfied, then we can access the feature we need. 😉

It is best to have separate methods for each specific action, such as Capture new Photo or Select a new Photo from Gallery and those methods should return the resulting ImageSource object or default failure value.

Camera Feature – TakePhoto()

Here’s the method implementation that you can use to Capture Photo using the device Camera and return an ImageSource upon success.

public async Task<ImageSource> TakePhoto()
{
	if (!CrossMedia.Current.IsCameraAvailable ||
			!CrossMedia.Current.IsTakePhotoSupported)
	{
		await DisplayAlert("No Camera", 
                    "Sorry! No camera available.", "OK");
		return null;
	}

	var isPermissionGranted = await RequestCameraAndGalleryPermissions();
	if (!isPermissionGranted)
		return null;

	var file = await CrossMedia.Current.TakePhotoAsync(new 
        Plugin.Media.Abstractions.StoreCameraMediaOptions
	{
		Directory = "TestPhotoFolder",
		SaveToAlbum = true,
                PhotoSize = PhotoSize.Medium,
	});

	if (file == null)
		return null;

	var imageSource = ImageSource.FromStream(() =>
	{
		var stream = file.GetStream();
		return stream;
	});

	return imageSource;
}

You can easily use this for a Page behind code implementation or a Service layer implementation for Capturing Photos.

StoreCameraMediaOptions provides you with a whole bunch of features you can easily use to customize and resize the captured Photo within the library itself. 😀

Gallery Feature – SelectPhoto()

Here’s the method implementation that you can use to Select Photo using the device Gallery and return an ImageSource upon success.

public async Task<ImageSource> SelectPhoto()
{
	if (!CrossMedia.Current.IsPickPhotoSupported)
	{
		await DisplayAlert("Photos Not Supported", 
                   "Sorry! Permission not granted to photos.", "OK");
		return null;
	}

	var isPermissionGranted = await RequestCameraAndGalleryPermissions();
	if (!isPermissionGranted)
		return null;

	var file = await Plugin.Media.CrossMedia.Current.PickPhotoAsync(new 
        Plugin.Media.Abstractions.PickMediaOptions
	{
		PhotoSize = Plugin.Media.Abstractions.PhotoSize.Medium,
	});

	if (file == null)
		return null;

	var imageSource = ImageSource.FromStream(() =>
	{
		var stream = file.GetStream();
		return stream;
	});

	return imageSource;
}

In both above methods we are first checking the availability of the feature, and then the status of the permission, before we make the call to Media Plugin.

You can see that upon successful execution completion we’re returning the retrieved ImageSource, otherwise in any case of failure we return null. Also you can remove DisplayAlert() set up, if you’re using a Service layer, instead just throw an Exception which you can handle at the point of execution. 😉

Permission Checkup!

As you can see we have a method call to RequestCameraAndGalleryPermissions() which checks for the Permission status for the features we need to access, which implements as follows.

private async Task<bool> RequestCameraAndGalleryPermissions() 
{
	var cameraStatus = await CrossPermissions.Current.
	CheckPermissionStatusAsync(Permission.Camera);
	var storageStatus = await CrossPermissions.Current.
	CheckPermissionStatusAsync(Permission.Storage);
	var photosStatus = await CrossPermissions.Current.
	CheckPermissionStatusAsync(Permission.Photos);

	if (
	cameraStatus != PermissionStatus.Granted || 
	storageStatus != PermissionStatus.Granted || 
	photosStatus != PermissionStatus.Granted)
	{
		var permissionRequestResult = await CrossPermissions.Current.
		RequestPermissionsAsync(
			new Permission[] 
			{ 
				Permission.Camera, 
				Permission.Storage, 
				Permission.Photos 
			});

		var cameraResult = permissionRequestResult[Permission.Camera];
		var storageResult = permissionRequestResult[Permission.Storage];
		var photosResults = permissionRequestResult[Permission.Photos];

		return (
			cameraResult != PermissionStatus.Denied &&
			storageResult != PermissionStatus.Denied &&
			photosResults != PermissionStatus.Denied);
	}

	return true;
}

We’re check for Camera, Storage, Photos access permission status, which are required for Camera and Gallery access from the User in all the platforms. As you can see based on the existing status we request the Permission from user, and return the results. This will prompt the user with the popups asking for Permission to access. 😀

A better, Permission Checkup!

Just to make it more cleaner and decoupled, here’s an improved Permission check up method where you can pass in the exact Permission you need to check and it will take care of it. Oh and this is very much reusable for any kind! 😉

private async Task<bool> RequestPermissions(List<Permission> permissionList)
{
	List<PermissionStatus> permissionStatuses = new List<PermissionStatus>();
	foreach (var permission in permissionList)
	{
		var status = await CrossPermissions.Current.
		CheckPermissionStatusAsync(permission);
		permissionStatuses.Add(status);
	}

	var requiresRequesst = permissionStatuses
                                 .Any(x => x != PermissionStatus.Granted);

	if (requiresRequesst)
	{
		var permissionRequestResult = await CrossPermissions.Current.
		RequestPermissionsAsync(permissionList.ToArray());
		
		return permissionRequestResult
			.All(x => x.Value != PermissionStatus.Denied);
	}

	return true;
}

You simply have to pass in the Permission you want to check for as follows,

public async Task<ImageSource> TakePhoto()
{
	...
	var isPermissionGranted = await RequestPermissions
	(new List<Permission>(){ Permission.Camera, Permission.Storage }); 
	if (!isPermissionGranted)
		return null;
	...
}

public async Task<ImageSource> SelectPhoto()
{
	...
	var isPermissionGranted = await RequestPermissions
	(new List<Permission>(){ Permission.Photos }); 
	if (!isPermissionGranted)
		return null;
	...
}

You can pass in any kind of Permission type for check and request for Granted status.

Exception Handle!

You can see I’m not handling exceptions in here, that I would leave to the execution point of these methods calls.

try
{
	var result = await SelectPhoto();
	if (result != null)
		viewPhotoImage.Source = result;
}
catch (Exception ex)
{
	// handle your exception
}

This I believe the best way to handle any exceptions that could occur, could be in your ContentPage code behind or ViewModel. 😀

Main Thread!

Unless you’re calling these features of Media Plugin from a code behind Event handler, then you need to make sure this is executed on the app’s Main Thread.

https://theconfuzedsourcecode.wordpress.com/2020/01/27/behold-the-check-list-of-media-plugin-set-up-for-xamarin-forms/#Run-on-UI-Thread

If you ever run into any issues, make sure you have gone through my previous blog post: Behold the check-list of Media Plugin set up for Xamarin.Forms! which will definitely help you tackle any issues easily!

Well that sums it up the whole set up and a bit of under the hood check up!

Fire up the Demo!

So just for this article I created a simple demo that reflects all of this recipe of better implementation of Media Plugin for Xamarin.Forms!

Check it on my github: github.com/XFMediaPluginDemo

Side by side on Android, iOS, and UWP!

Conclusion

Following this guide you can easily implement the Media Plugin for Xamarin.Forms with a proper maintainable architecture! Although setting up might seem a bit tedious, its actually quite straight forward. Like I’ve shown in the code you need to handle Async Await calls properly and up to the UI Thread and exception handling.

Some of those bits that I have shared here aren’t mentioned in the plugin docs yet, since they’re out of date. So I really hope this helps you fellow devs!

Share the love! 😀 Cheers!

Behold the check-list of Media Plugin set up for Xamarin.Forms!

Let me share a check list for easily implementing the Media Plugin (Xam.Plugin.Media) for Xamarin.Forms with a peace of mind! 😉

Here I’m sharing some important bits that you need to focus on to avoid running into any obnoxious issues during run time of your Xamarin.Forms app!

Backstory…

Recently I was implementing Media Plugin library (Xam.Plugin.Media) in one of my Xamarin.Forms projects, even though I had implemented this before, I ran into some missing bits that caused some problems, so I had to Google them out.

So after resolving my implementation I thought of writing up this article to sum up a check list that you need to go through to make sure you’ve set up your project properly for the Media Plugin to work, hassle free, giving you a peace of mind! 😉

Media Plugin – Xam.Plugin.Media!

Xam.Plugin.Media is the free Plugin Library by James Montemagno, that allows us to easily interact with Capturing Photos and Video and accessing them from the device Galley using Xamarin.Forms!

Github: https://github.com/jamesmontemagno/MediaPlugin
Nuget: http://www.nuget.org/packages/Xam.Plugin.Media

There’s a little intro to the Media Plugin, then let’s jump right in!

Behold the check list!

It is quite straight forward how to set up Media Plugin with the guidelines of the official docs in github repo, but there are a few bits that you need to focus on as follows…

1. On Android: CurrentActivity Plugin!

You need to install Android CurrentActivity Plugin using the Nuget package manager, and properly set up the MainApplication Class set up. This used to be automatically set up during the installation from nuget but it doesn’t seem to be doing that so far, so you need to manually set it up yourself.

#if DEBUG
[Application(Debuggable = true)]
#else
[Application(Debuggable = false)]
#endif
public class MainApplication : Application
{
    public MainApplication
      (IntPtr handle, JniHandleOwnership transer)
      : base(handle, transer)
    {
    }

    public override void OnCreate()
    {
        base.OnCreate();
        CrossCurrentActivity.Current.Init(this);
    }
}

Also you need to initialize CrossCurrentActivity.Current instance in MainActivity.OnCreate() method.

public class MainActivity : global::Xamarin.Forms.Platform.Android.FormsAppCompatActivity
{
    protected override void OnCreate(Bundle savedInstanceState)
    {
        ...
        
        base.OnCreate(savedInstanceState);

        CrossCurrentActivity.Current.Init(this, savedInstanceState);

        Xamarin.Essentials.Platform.Init(this, savedInstanceState);
        global::Xamarin.Forms.Forms.Init(this, savedInstanceState);
        LoadApplication(new App());
    }
    
    ..
}

2. On Android: Permission Plugin set up!

When you install the Xam.Plugin.Media it will come with the Plugin.Permissions library references inside it. For this to work properly on Android you need to make sure to set up its native handlers on Android in the MainActivity.OnRequestPermissionsResult() method override.

public override void OnRequestPermissionsResult(int requestCode, string[] permissions, [GeneratedEnum] Android.Content.PM.Permission[] grantResults)
{
    Xamarin.Essentials.Platform.
       OnRequestPermissionsResult
       (requestCode, permissions, grantResults);

    Plugin.Permissions.PermissionsImplementation.
       Current.OnRequestPermissionsResult
       (requestCode, permissions, grantResults);

    base.OnRequestPermissionsResult
       (requestCode, permissions, grantResults);
}

If you’re using Xamarin.Essentials already in your app or you’ve created your Xamarin.Forms Project recently with an update Visual Studio 2019, then OnRequestPermissionsResult() override should already exist in your MainActivity class. In that case just add the PermissionsImplementation.Current.OnRequestPermissionsResult(..) snippet to the method. Well I actually missed out on on this and I ran into some weird issues on Android.

3. On Android: FileProvider set up!

Make sure to set up the FileProvider in AndroidManifest along side the xml/file_paths.xml file in the Resources directory. One crucial point to keep in mind is that there are two ways you can set up the android:authorities value in the FileProvider.

  • android:authorities=”${applicationId}.fileprovider”
  • android:authorities=”com.example.android.fileprovider”

Sometimes it can be confusing when you are setting up this value, as shown above, either keep it as the first option as it is or the second option, with your app package name “<your app package name>.fileprovider” minted. For the clarity of it though I would suggest sticking to the first option as shown in the docs as well.

<?xml version="1.0" encoding="utf-8"?>
<manifest ... >
    <uses-sdk ... />
    <application ... >
    ...
    <provider android:name="android.support.v4.content.FileProvider"
                android:authorities="${applicationId}.fileprovider"
                android:exported="false"
                android:grantUriPermissions="true">
      <meta-data android:name="android.support.FILE_PROVIDER_PATHS"
                android:resource="@xml/file_paths"></meta-data>
    </provider>
    ...
  </application>
    ...
</manifest>

4. CrossMedia.Current.Initialize();

You need to make sure to initialize the Media Plugin before calling up any of its method functions. You can do this on Xamarin.Forms layer, or even in Platform Nodes, but preferably on the Page that you’re intending to use the plugin.

You should set it up on App.xaml.cs start up methods if you’re intending to use Media Plugin on multiple pages in your App.

public partial class App : Application
{
    public App()
    {
        InitializeComponent();

        Plugin.Media.CrossMedia.Current.Initialize();

        MainPage = new NavigationPage(new MainPage());
    }
}

If you’re abstracting it out to a Service instance, then you can call this up in the Constructor during instantiation as well.

5. Run on UI Thread!

Unless you’re calling up the Media Plugin’s functions in an Event Handler directly invoked by a UI Element, you need to make sure you’re running on UI Thread during the run time. Otherwise you could run into various kinds of issues since, since accessing Camera or Gallery relies heavily on Native IO operations.

Therefore make sure to run it on UI Thread, by either using default Xamarin.Forms UI Thread force invoke method, Device.BeginInvokeOnMainThread() as below,

Device.BeginInvokeOnMainThread(async () =>
{
	await Plugin.Media.CrossMedia.Current.TakePhotoAsync(...);
});

...

Or if you’ve got Xamarin.Essentials installed in your project, then you can use MainThread Helper it provides a neat way to check for the execution thread, and based on that force the execution on UI Thread,

if (!MainThread.IsMainThread)
{
    await Plugin.Media.CrossMedia.Current.TakePhotoAsync(...);
}
else 
{
    MainThread.BeginInvokeOnMainThread(() =>
    {
        await Plugin.Media.CrossMedia.Current.TakePhotoAsync(...);
    }); 
}

...

6. Perform Permission check up!

It is best perform a Permission availability check up for the features that you’re accessing from Media Plugin using the Permission Plugin, that’s referenced along with it. This is something that’s recommended in the Media Plugin’s docs as well, which you will find at the end though. But in my experience this is a crucial set up to have an extra assurance of the features you’re trying to access from Media Plugin.

Basically before each call to Capture or Pick any Photo/Video from the Media Plugin, you need to check for the availability of the Permission for Camera, Storage, and Photos. Initially as shown below…

private async Task<ImageSource> TakePhoto()
{
    ...
    
    var isAccessGranted = await RequestCameraAndGalleryPermissions();
    
    ...
}

private async Task<bool> RequestCameraAndGalleryPermissions() 
{
    var cameraStatus = await CrossPermissions.Current.
                CheckPermissionStatusAsync(Permission.Camera);
    var storageStatus = await CrossPermissions.Current.
                CheckPermissionStatusAsync(Permission.Storage);
    var photosStatus = await CrossPermissions.Current.
                CheckPermissionStatusAsync(Permission.Photos);
    ...

    // request access permissions

    ...
}

If they’re not Granted yet or denied you need to launch a request for them from the User during the run time. I must note that the github docs of the Permission plugin are outdated and doesn’t reflect the latest changes of the library. I will be sharing the full implementation of this code snippet later in this article.

7. Set up Required Permissions!

Some of those permission requirements you need to define in the device native configuration in Android -> AndroidManifest.xml, iOS -> Info.plist, and UWP -> Package.appxmanifest. This is well documented in the Media Plugin’s docs.

https://github.com/jamesmontemagno/MediaPlugin#important-permission-information

8. Set up Required Permissions! only!

Yes it’s better not to set up Permissions unless you absolutely need them, according to your requirement. Let’s say you’re only using the Media Plugin to access Gallery, then you don’t need to set up required Permissions for Camera, and data Write Access. This will also give an extra peace of mind for your Users as well. 😉

9. Re-usable code!

If your apps is going to be using Camera and Gallery usage all over the in multiple pages, then it’s better to implement a separate Service layer for it using the Media Plugin.

This will definitely come in handy when you’re dealing with a good MVVM architecture in your project solution. You can abstract out the required features into a Service instance, that’s best registered as a Singleton object in your IoC Container.

public MediaService : IMediaService
{
	public MediaService()
	{
		...
	}
	
	public async Task<ImageSource> CapturePhoto()
	{
		...
	}
	
	public async Task<ImageSource> SelectPhoto()
	{
		...
	}
	
	...
}

As an added extra you could have a Permission check up method, where you pass in the type of permissions you want to request from User unless already granted.

...
private async Task<bool> RequestPermissions(List<Permission> permissionList)
{
    ...
}
...

Well.. that’s basically the check list you need to go through when setting up Media Plugin in your Xamarin.Forms! 😉

Conclusion…

Even though its straight forward to set up the Media Plugin (Xam.Plugin.Media) for Xamarin.Forms, there’s a high chance you might miss something during the process and run into all kinds of weird issues during the run time, specially since there’s some platform specific bits to set up as well!

I’ve also shared some tips at the end for setting up the usage of it to cater for a better implementation. I might write up another post sharing a step by step guide for setting up all these bits in my next article! Until then, hope this helps!

Share the love! 😀 Cheers!

Building a bi-directional interop bridge with WebView in Xamarin.Forms!

Let’s build an advanced communication bridge into your Xamarin.Forms WebView, talk to it, and let it talk back to us at will!? 😉 lol Yes let me show you how to pass data from Javascript environment to C# .NET run time in the Web page rendered inside your Xamarin.Forms WebView!

I’m talking about building a bi-directional communication tunnel with HTML/Javascript inside your WebView in Xamarin.Forms yo! 😀 buckle up your seatbelts!

So in my previous article, Talking to your WebView in Xamarin.Forms! I talked about, how to build a uni-directional C# .NET to Javascript environment in Xamarin.Forms WebView.

WebView in Xamarin.Forms..

In this article I’m going to take another step forward and allow the same functionality to occur the other way around as well… We’re talking about a two-way invoking between .NET run time and javascript run time in a Xamarin.Forms WebView!

Unfortunately this cannot be done by default in WebView.

Behold, Hybrid WebView!

This right here is a bit more advanced extension of the WebView with a bit of Xamarin Native magic! 😉 In order to establish an invoke bridge directly from HTML Javascript sandbox that its running inside the WebView, out to the .NET runtime, we need something more natively handled in Xamarin!

Basically we’re going to implement a device native script handler for the WebView which is going to handle the bridging between the Javascript and the .NET runtime handshake, in return giving us the opportunity to invoke calls from javascript into the .NET run time the Xamarin.Forms is execution on! 😉

Well that’s a very simplistic explanation, but there’s a whole article about it on Microsoft Xamarin Docs, Customizing a WebView if you’re interested! Since its already there, I wouldn’t be going into complete details of it, rather I would be explaining the improved implementation I have done on top of it for the Hybrid WebView.

Over there it focuses on loading Embedded HTML content, but I will extend my implementation to support for dynamic HTML content, allowing you to handle javascript loaded from a Web Source and support even run time generated javascript.

Invoking C# from Javascript in the WebView!

In order to do this, in par with Xamarin.Forms WebView, we need to implement a Custom Renderer for WebView, which we will refer to as HybridWebView.

HybridWebViewRenderer will be created across all the native platforms we intend to use our HybridWebView, in Android, iOS and Windows native environments each equipped with its own javascript handler to build a bridge on to our .NET run-time. 😉

We access the native WebViewRenderer properties and basically implement a special handler to listen to a certain pre-defined Javascript method execution. In this method which we add into the javascript that is rendered inside the WebView, we will define the parameters we need to use, in that way we can pass any number of parameters and data types as we want.

We’re going to intercept the execution of this javascript method inside our Hybrid WebViewRender, and then redirect it on to the .NET method we’ve subscribed to. So in the Hybrid WebView definition we will have an Action method that we bind to in our Xamarin.Forms level which we will subscribe to wherever we’re using this magical bits! 😉

Let the coding begin!

Let’s begin with HybridWebView Control in Xamarin.Forms! Here we;re adding an Action that we will subscribe to in order to receive data from Javascript invokes inside the WebView rendered content.

HybridWebView

namespace XFWebViewInteropDemo.Controls
{
    public class HybridWebView : WebView
    {
        private Action<string> _action;

        public void RegisterAction(Action<string> callback)
        {
            _action = callback;
        }

        public void Cleanup()
        {
            _action = null;
        }

        public void InvokeAction(string data)
        {
            if (_action == null || data == null)
            {
                return;
            }
            _action.Invoke(data);
        }
    }
}

 

InvokeAction is the method that will be used by the Native Renderer object to direct the invokes from javascript executions. Using the RegisterAction we can dynamically register the Action we need to subscribe to.  You can add any number of parameters as you wish in here, but you need to make sure to handle them in the native renderer as well.

Native Renderers…

We’re going to build native renderers for each platform we’re targeting, Android, iOS, and UWP (Windows). Basically all the renderers follow the same basic concept as we discussed before, but each of their implementation is going to be different based on the platform.

We need to make sure to handle the subscribe and unsubscribe of the Element Native properties and events properly in the renderer’s OnElementChanged() event.

We’re going to inject the javascript method that we’re going to listen to in the renderers as following.

private const string JavaScriptFunction = "function invokeCSharpAction(data){....}";

 

We will be defining this in each renderer, according to the native platform. Every time a invokeCSharpAction() javascript method executes inside the WebView, it will get fetched by the Renderer and the following method call will occur.

((HybridWebView)Element).InvokeAction(value);

 

Up to the HybridWebView’s Action subscription on Xamarin.Froms run time, allowing our Action to fire up and retrieve the data coming in from javascript.

Alright now let’s get into details of each native renderer.

Android Renderer!

We’re going to use the Android’s WebViewRenderer to subclass our HyrbidWebViewRenderer.

github: /XFWebViewInteropDemo.Android/Renderers/HybridWebViewRenderer.cs

Like we discussed before for Android, we have the following script injection defined,

private const string JavascriptFunction = "function invokeCSharpAction(data){jsBridge.invokeAction(data);}";

 

For Android we need some extra bits of implementation, by creating a JavascriptWebViewClient that will set up listening to the execution of javascripts inside the WebView.

Then we have to create a JsBridge, which handles the interfacing with Javascripts, and fires up InvokeAction() method to redirect the execution flow up to the Xamarin.Forms level handlers.

Both those custom objects need to be set up in the HybridWebView in the renderer Element upon instantiation.

Control.SetWebViewClient
(new JavascriptWebViewClient($"javascript: {JavascriptFunction}"));
Control.AddJavascriptInterface
(new JsBridge(this), "jsBridge");

 

Once all that set up, and you build the Android project straight away, you might be getting a build error as following. (unless you’ve set this fix up before in your project)

Its caused by the JsBridge class we implemented with an Export attribute for the invokeAction method for our renderer, to export this into a native java method. So we need to add the Mono Android Export library.

You can fix this by going to Android Project -> References -> Add References -> Select Assemblies tab on the left panel -> tick on Mono.Android.Export Reference from the list of References.

Click Ok and rebuild, you’re all set! 😉

That’s pretty much it for the Android Renderer. Next on to iOS…

iOS Renderer!

For iOS we are going to use WkWebViewRenderer as the base renderer for our HybridWebView and in addition we have to implement IWKScriptMessageHandlder interface to handle the custom javascript execution monitoring that we target to handle.

github: /XFWebViewInteropDemo.iOS/Renderers/HybridWebViewRenderer.cs

We set up a WKWebViewConfiguration object in the constructor and we get access to the property WKWebViewConfiguration.UserContentController which allows us to set up our native bridge to Javascript execution firing up inside the WebView.

public HybridWebViewRenderer(WKWebViewConfiguration config) : base(config)
{
    _userController = config.UserContentController;
    var script = new WKUserScript(new NSString(JavaScriptFunction),
                   WKUserScriptInjectionTime.AtDocumentEnd, false);
    _userController.AddUserScript(script);
    _userController.AddScriptMessageHandler(this, "invokeAction");
}

 

Then for iOS, we have the following script injection defined using webkit API, accessing the invokeAction script that we attached and finally calling on the postMessage() method with the data parameter.

private const string JavaScriptFunction = "function invokeCSharpAction(data){window.webkit.messageHandlers.invokeAction.postMessage(data);}";

 

IWKScriptMessageHandler provides us with DidReceiveScriptMessage() method which we use to transfer the data up to the Xamarin.Forms level handler using, HybridWebView.InvokeAction(data).

Quite simple ans straight forward eh! next to Windows, or UWP as you might prefer.. 😉

UWP Renderer!

We use the Xamarin native WebViewRenderer for UWP or Windows platform.

github: /XFWebViewInteropDemo.UWP/Renderers/HybridWebViewRenderer.cs

The native default renderer grants us access to these two events NavigationCompleted and ScriptNotify. We need to make sure to subscribe to those events in our HybridWebViewRenderer in Windows as follows.

Control.NavigationCompleted += OnWebViewNavigationCompleted;
Control.ScriptNotify += OnWebViewScriptNotify;

 

NavigationCompleted, allows is to easily inject our javascript handler function, which is defined as follows for UWP or Windows,

private const string JavaScriptFunction = "function invokeCSharpAction(data){window.external.notify(data);}";

 

And then ScriptNotify, provides us the chance to redirect back the execution to Xamarin.Forms level handler using HybridWebView.InvokeAction(data).

Bingo, that completes the UWP or Windows Renderer!

Now that we’ve finished the setting up of our HybridWebView and its Native Renderer for Android, iOS and Windows, its time to consume it and taste it out! 😉

Let’s try it out!

Here’s we shall begin by consuming it in a XAML page in Xamarin.Forms!

<controls:HybridWebView
	x:Name="webViewElement"
	HorizontalOptions="FillAndExpand"
	VerticalOptions="FillAndExpand" />

github: /XFWebViewInteropDemo/HybridWebViewDemoPage.xaml

And then don’t forget to Subscribe to retrieve the data coming in from javascript inside our WebView using RegisterAction() method we created!

...
    // Subscribe for the data coming in from Javascript
    webViewElement.RegisterAction(DisplayDataFromJavascript);
}

private void DisplayDataFromJavascript(string data)
{
    Device.InvokeOnMainThreadAsync(() =>
    {
        ...
        // Do whatever you want with the data
        ...
    });
}
...

github: /XFWebViewInteropDemo/HybridWebViewDemoPage.xaml.cs

I’m just going to use the Main UI Thread’s help to execute any UI related stuff. And here’s a little demo HTML that I’m setting up in our Hyrbid WebView.

webViewElement.Source = new HtmlWebViewSource()
{
    Html =
        $@"<html>" +
        "<head>" +
            ...
            "<script type=\"text/javascript\">" +
                "function invokexamarinforms(){" +
                "    try{" +
                "        var inputvalue = 
document.getElementById(\"textInputElement\").value;" +
                "        invokeCSharpAction(inputvalue + '. This is from Javascript in the WebView!');" +
                "    }" +
                "    catch(err){" +
                "        alert(err);" +
                "    }" +
                "}" +
            "</script>" +
            ...
        "</head>" +

        "<body>" +
            "<div>" +
                "<input type=\"text\" id=\"textInputElement\" placeholder=\"type something here...\">" +
                "<button type=\"button\" onclick=\"invokexamarinforms()\">Send to Xamarin.Forms</button>" +
            "</div>" +
        "</body>" +

        "</html>"
};

github: /XFWebViewInteropDemo/HybridWebViewDemoPage.xaml.cs

As you can see I have a javascript function, invokexamarinforms() that will get invoked from a button call in the body. Once this method executes, it calls on the invokeCSharpAction() method that we defined in our Hybrid WebViews Native renderers.

In my javascript snippet I’m surrounding this call with a try catch in order to make sure the Native Renderer is properly implemented or not. Making sure this method is properly executes is a crucial step during debug if you run into any issues.

So let’s try out that sample code bits in action!

Time for some action! 😉

Hit that F5 yo! (well.. if you’re in Visual Studio! lol)

Side by side iOS, Android and UWP working like charm! 😉

As you can see in my simple Xamarin.Forms demo, I am demonstrating a simple C# .NET to Javascript call with data and Javascript to C# .NET call with data, a true bi-directional communication bridge!

Here we are typing some text in the Xamarin.Forms Entry element and sending it into the HTML inside the WebView. And then typing some text in the HTML Text Input element inside the WebView and click on HTML Button, and sending it to the Xamarin.Forms Label to be displayed, works like a charm!

I have shared the demo app code in my github as usual: github.com/XFWebViewInteropDemo

A little chat conversation between Javascript to C# and vise-versa! 😉

Yeah just a fun little demo I have added to the same repo in github! 😀

Extra tips!

Yep it’s that time, for some extra tips based on my experience with Xamarin.Forms Hybrid WebView! Although the extra tips that I already discussed in my previous article Talking to your WebView in Xamarin.Forms! still applies for this as well since we’re still extending from default Xamarin.Forms WebView, but apart from that…

Web Source, Embedded, Code HTML!? all same!

Doesn’t matter whatever the source of the HTML you’re setting in the Hybrid WebView, be it a web source directly from a URL, or loading an embedded HTML File, or even a code generated dynamic HTML content, it doesn’t make a difference.

The only thing that matters is the invokeCSharpAction() in your rendered HTML, so that the native renderers can pick it up and forward the execution to Xamarin.Forms .NET handlers!

Yes! extra parameters!

Even though I’m showcasing only a single parameter during this demo article, from javascript to C# .NET run time, you can easily extend this same implementation to pass any number of parameters as you wish! As I explained in the article make sure to define it in the following bits,

HybridWebView.InvokeAction(string data1, string data2)

Something to keep in mind is that you can only pass a single parameter into the invokeCSharpAction(data).  So in your javascript make sure to merge all the parameters into a single value and have a pipe delimiter (ex: |) like separator for them (ex: data1|data2) that you’re before to the invokeCSharpAction(data) method, which you will break it up on arrival in the native renderer and pass them up to the InvokeAction(data1, data2).

var dataBody = data;
var dataArray = dataBody.Split("|");
var data1 = dataArray[0];
var data2 = dataArray[1];

((HybridWebView)Element).InvokeAction(data1, data2);

Finally wire it all up, you’re good to go! 😉 I might share another article with some cool implementation with this in near future! 😀

Conclusion

You can easily build a communication bridge from C# .NET to javascript environment in Xamarin.Forms WebView! but the other way is not really possible out of the box!

That’s why we’re implementing this Hybrid WebView Control which allows us build a communication bridge from javascript to C# .NET environment directly during run time! 😉

So this concludes my bi-directional communication tunnel with HTML/Javascript inside your WebView in Xamarin.Forms yo!

Well that’s pretty much it!

Share the love! Cheers! 😀

Talking to your WebView in Xamarin.Forms!

Let’s build a communication bridge into your Xamarin.Forms WebView, and talk to it!? 😉 lol Yes let me show you how to pass data into the Web page rendered inside your Xamarin.Forms WebView!

I’m talking about building a uni-directional communication with Javascript inside your WebView in Xamarin.Forms yo! 😀 get your game face on!

WebView in Xamarin.Forms..

Xamarin.Forms provides a neat WebView that could render any Web HTML content efficiently similar to a browser inside your own Xamarin.Forms App.

Earlier there used to be a lots of issues that needed to be dealt with when to comes to rendering HTML content alongside Javascript inside the WebView, but with the recent update it has gotten far better with lots of features and facilities straight out of the box to be used! 😀

Invoking Javascript in the WebView!

Using the WebView straight out of the box, we can execute Javascript methods rendered inside the HTML content. Now I know this used to require a lot hacks and tricks, along side dealing with lot of run time exceptions.

But in the most recent updates of Xamarin.Forms, the WebView has gotten rock solid, and now even provides a dedicated method, EvaluateJavaScriptAsync() to invoking Javascript methods straight out of the box.

WebView.EvaluateJavaScriptAsync(String)

 

So now you can execute Javascript methods along with data parameters from you C# code in Xamarin.Forms using the default WebView control. EvaluateJavaScriptAsync() is an async method that lets you execute javascript and even await the call to response from the invoke as well.

var result = await webView
        .EvaluateJavaScriptAsync
            ("javascriptmethod('Hello world!')");

 

All you need to do is call the javascript method you’re targeting to invoke with or without the parameters you prefer using EvaluateJavaScriptAsync() in an asynchronous manner allowing you to await for a result back from the javascript into the .NET environment itself! Yep its that simple to talk to the HTML content in your WebView now! 😀

Let’s give it a try and establish a uni-directional communication with our WebView! 😉

Let the coding begin!

Here I have prepared a small demo where I’m loading some HTML content, along with a nice little javascript bits, into my WebView using HtmlWebViewSource as follows…

webViewElement.Source = new HtmlWebViewSource()
{
    Html =
        $@"<html>" +
        "<head>" +
            ...
            "<script type=\"text/javascript\">" +
                "function updatetextonwebview(text) {" +
                "    document.getElementById
                     (\"textElement\").innerHTML = text;" +
                "}" +
            "</script>" +
            ...
        "</head>" +

        "<body>" +
        ...
        ...
        "</body>" +

        "</html>"
};

Full code on github: /XFWebViewInteropDemo/DefaultWebViewDemoPage.xaml.cs

So here in my HTML content, I have a simple Javascript method, updatetextonwebview(text) where it takes in a value and set it to an HTML text element in the body. Pretty simple and straight forward.

string result = await webViewElement
        .EvaluateJavaScriptAsync
           ($"updatetextonwebview('{textEntryElement.Text}')");

 

And then I take a Text value from an Entry Element and pass it into the updatetextonwebview() javascript method using EvaluateJavaScriptAsync() of WebView.

Alright, let’s try it out!

Hit F5!

Well if you’re on Visual Studio, just hit F5 and watch the magic!

Side by side iOS, Android and UWP with Xamarin.Forms right out of the box! 😉

As you can see in my simple Xamarin.Forms demo, I have an Entry element which I type some text into and then I click on the Button which then going to pass that text data into the WebView’s javascript method. Then inside the javascript, it takes in the data and set it to a text label in the HTML body.

I have shared the demo app code in my github as usual: github.com/XFWebViewInteropDemo

No hacks, no work arounds, no custom renders, just straight out of the box in Xamarin.Forms! Works like a charm! 😉

Extra tips!

Yep it’s that time, for some extra tips based on my experience with Xamarin.Forms WebView!

-Track invoking of Javascript

Using WebView.EvaluateJavaScriptRequested event you can track the javascript invoke calls injecting into the WebView from your .NET code, basically an monitoring mechanism of all your javascript invokes from C# which will allow you to validate them or add extra details as you prefer on demand.

-Track Navigation inside the WebView

WebView provides a whole list of events to track the navigation now, along side back and forward navigation, redirects, and even refresh events.

WebView.Navigating

This event Triggers upon the beginning of the Navigation, allowing you to cancel it on demand. This event provides a WebNavigatingEventArgs object which provides you all the details about the navigation that is about to occur, direction, url endpoint and so on.

This also provides WebNavigatingEventArgs.Cancel property which allows you to cancel that navigation on demand. So yeah a lot of cool bits you can do with it!

WebView.Navigated

This event Triggers after a Navigation completes, providing you with the same details similar to Navigating event. In addition it gives WebNavigatedEventArgs.Result property which tells you whether the navigation was success or failure.

WebView.GoBackRequested | GoForwardRequested | ReloadRequested

Now these are some simplified events thats provided by WebView, allowing you to directly hook into GoBack, GoForward and Reload events when they occur. Although they do not provide facility to cancel those events like how we get in Navigating event. Just a quick easy way to monitor those events as they occur.

-Think Creative!

Most developers miss this point, if you can send a simple text string, then you can pass anything into the WebView’s javascript. Well… in disguise of a string of course!

  • Get device native data
  • Location GPS data
  • Proximity data
  • Internet Connectivity data
  • Captured File/Image data

Those are few examples, yes even an Image captured from the device camera can easily be sent as a byte array converted into a base64 string!  Imagination is the limit yo! 😉

Conclusion

Xamarin.Forms WebView has come a long way since the early days, into a complete mature sandbox environment to render any HTML Web Content inside your Xamarin.Forms app. And it provides lots of features to communicate, pass data back and forth, and even monitor and control the navigation happens inside itself.

This article basically focuses on uni-directional execution from C# .NET code to Javascript environment, while you can still await for the results from the javascript.

But there is no direct execution from Javascript environment to C# .NET yeah? So in my next article I’ll share how to build a bi-directional execution from C# .NET code to Javascript environment with Xamarin.Forms WebView. 😉

Well that’s pretty much it!

Share the love! Cheers! 😀

Xamarin.Forms Native HttpClientHandler for HttpClient…

Let’s make sure our Xamarin.Forms apps are properly configured with Native HttpClientHandler for optimum performance and better network security..

If you’re using the HttpClient for making Web API calls outside your app, you probably using the HttpClientHandler to set up various kinds of configuration for the HttpClient instance.

Now this HttpClient and Native HttpClientHandler applies directly for both Xamarin Native and Xamarin.Forms apps…

Although in this article I’m focusing on Xamarin.Forms, the same configuration set up can be used for any Xamarin Native apps as well.  By default in Xamarin you can use either the Managed HttpClientHandler which is fully maintained by .NET mono run time or the Native HttpClientHandler that maps itself to the Native run time configuration.

Why Native HttpClientHandler?

Thanks to the awesomeness of the Xamarin and the powerful Xamarin.Forms ability to map itself efficiently to the Native device environment, provides you with this facility to use the device Native Network Layer’s configuration in your Apps as well.

  • Using the Native HttpClientHandler provides you with a lot of advantages in terms of Network Communication Layer, which maps itself completely to the native properties and behaviors.
  • It provides your App with the in built default System native Security such as Transport Layer Security, TLS 1.2 features. This is basically built in for both Android and iOS system devices by default, which then we can leverage automatically on to our Xamarin.Forms app as well during run time.
  • This gives the user a peace of mind, in terms of the security of the network communication in the app while also giving the user the free of choice to let the app inherit itself the system configured security settings.
  • Defaulting to the Native Network configuration we can make sure our app is fine tuned for Security and Performance on the device native level and you do not have to spend extra time managing those bits manually.
  • Another great advantage is not needing to manually handle device Proxy Settings, allowing your Xamarin.Forms app to communicate through the device’s default network tunnel.

Well that’s pretty much a good list of reasons to make sure to set up our Xamarin.Forms apps to use the Native HttpClientHandlers eh! 😉

So what are they?

So below are the Native HttpClientHandlers available in Xamarin run time for each Platform, which applies for Xamarin.Forms as well.

AndroidClientHandler -AndroidClientHandler is the new handler that delegates to native Java code and Android OS instead of implementing everything in managed code. This option has better performance and smaller executable size.

NSUrlSessionHandler -The NSURLSession-based handler is based on the native NSURLSession framework available in iOS 7 and newer. This options has better performance and smaller executable size, supports TLS 1.2 standard.

WinHttpHandler -WinHttpHandler is implemented as a thin wrapper on the WinHTTP interface of Windows and is only supported on Windows systems. Provides developers with more granular control over the application’s HTTP communication than the default HttpClientHandler class.

So here as you can see, using the device native HttpClientHandlers provides you with the best of performance and security for your app compared to opting to use the Managed HttpClientHandler where you have to manually handle those optimizations yourself.

Although I must make a note here, in Windows or UWP Xamarin apps the default set up is the .NET Managed HttpClientHandler because the underlying native environment is Windows itself. But opting to use WinHttpHandler provides arguably better advantage according to many documentation, and also it’s in the same .NET stack! 😉

What no to do?

So before we get into “the how?”, let’s first make sure the bits not to do in our app project!

– not use “Managed”

So when it comes to Xamarin.Forms, by default when you create your project in Visual Studio the Native project nodes Properties are set up to use the Native HttpClient Handlers already. You can see this in both Android and iOS Project settings,

  • Android project node -> Properties -> Android Options -> Click “Advanced”
  • iOS project node -> Properties -> iOS Build

Do not set it to option to “Managed” HttpClientHandler in either of those settings, which will opt you out of Native HttpClientHandler.

– not use “new HttpClientHanlder()” 

If the above Settings check success, the next thing to consider is not instantiating HttpClientHanlder on its own as below,

HttpClientHandler httpClientHandler = new HttpClientHandler();
...
// setting up httpClientHandler settings
...
...
HttpClient httpClient = new HttpClient(httpClientHandler);

 

This is something you should not do, which will override your Native project property set up regarding the HttpClientHandler, and opt your HttpClient to use Managed HttpClientHandler instead, resulting you losing all the native goodness!

Next let’s see what to do?

What to do?

Here are the things you need to make sure to do instead.

– not using HttpClientHandler!?

Consider not using HttpClientHandler at all with your HttpClient, then you’re basically good to go, as long as you have set it up in your App Project Native settings. Not a joke though! lol 😛

Just use plain HttpClient instance out of the box! but make sure to do the following as well.

– set Native HttpClientHandler!

Go to the following settings in each of your Xamarin.Forms Native project nodes,

  • Android project node -> Properties -> Android Options -> Click “Advanced”

  • iOS project node -> Properties -> iOS Build

Make sure to set the Native Android and NSUrlSessionHandler those settings, to opt to use AndroidClientHandler and iOS NSUrlSessionHandler for your HttpClientHandler by default.

Well UWP or Windows project nodes doesn’t have such settings as it by defaults use .NET Managed HttpClientHandler.

A little demo!

Now if its all good, you should be able to see the following behaviors in action,

So this is a little Xamarin.Forms demo that I prepared to demonstrate the behaviors of Native HttpClientHandlers on Android, iOS and Windows UWP.

Here I’m demonstrating the Network access (blue color access granted and red color access blocked in run time) for a list of scenarios,

Now you can see how each device Native environment handles those endpoint calls, basically only allowing access to trusted secure web endpoints in the native network tunnel to go through.

Well that was quite simple eh! but we all know the real life requirements wouldn’t be so simple, what if we need to use the HttpClientHandler in code?

Yes we need access to the Native HttpClientHandler in code!

So then let me walk you through handling an advance implementation of the native HttpClientHandler with more customization added in code! 😉 

How to? Advanced set up of Native HttpClientHandler!

Yes as you can see in the Project Settings, it doesn’t really give you much options to customize your Native HttpClientHandler settings, or even override some of its behaviors at all. In a real life scenarios you would definitely need some more access to your HttpClientHandler use in code.

Compared to the Managed .NET HttpClientHandler where you easily have access to all its properties and behaviors.

But it is crucial for us to stick to the Native HttpClientHandler, so the solution would be to implement an access to the Native HttpClientHandler in our Xamarin.Forms code.

– Under the hood!?

Thanks to the awesomeness of Xamarin we have full access to those Native HttpClientHandlers in code as well, so that we can use them as however as we like. Let’s take a look under the hood of these Native bits shall we,

Android:

iOS:

Windows:

Now you can see that all these Native Handlers are extending from either HttpClientHandler or the HttpMessageHandler,

Drilling down further into HttpClientHandler we can see that its extending itself from HttpMessageHandler.

– Using em in code!

Let’s start by using our AndroidClientHandler in code to be used with HttpClient instance.

var androidClientHandler = new AndroidClientHandler();
... 
// setting up native httpClientHandler settings
...
...
HttpClient httpClient = new HttpClient((HttpMessageHandler)androidClientHandler);

 

And for iOS with the NSUrlSessionHandler.

var iosClientHandler = new NSUrlSessionHandler();
... 
// setting up native httpClientHandler settings
...
...
HttpClient httpClient = new HttpClient((HttpMessageHandler)iosClientHandler);

 

Then for Windows or UWP, opt to our WinHttpHandler.

var uwpClientHandler = new WinHttpHandler();
... 
// setting up native httpClientHandler settings
...
...
HttpClient httpClient = new HttpClient((HttpMessageHandler)uwpClientHandler);

On Windows or UWP make sure to install nuget package: System.Net.Http.WinHttpHandler to use WinHttpHandler which is a far better native option than default HttpClientHandler.

As you can see we’re casting them to HttpMessageHandler as a common ground object, since they all inherit from that base.

Now that we’ve got access to them in code, we can access all their properties and behaviors, and even override to customize them as we wish to.

– build the bridge to Xamarin.Forms!

Since the above bits are not directly accessible from Xamarin.Forms, we need to build the bridge that will allow us to access the Native HttpClientHandler instance in Xamarin.Forms environment directly.

Since I already created a common ground instance across all the native environments with the casting to HttpMessageHandler, this is much easier. Now there are plenty of ways leverage the access to this object up towards Xamarin.Forms layer, but here I’m going to showcase rather a simple implementation.

code on github repo: XFNativeHttpClientHandler/Services/HttpClientService.cs

Here I have a simple Service implementation in Xamarin.Forms where it maintains a Singleton object of itself, which contains a HttpClient object and HttpClientHandler object.

Given the HttpClientHandler is provided, I am instantiating my HttpClient() on demand during the run time as you can see below.

private HttpClientService()
{
    HttpClient = HttpClientHandler != null ?
        new HttpClient((HttpMessageHandler)HttpClientHandler) 
      : new HttpClient();
}

public static HttpClientService Instance
{
    get
    {
        lock (Padlock)
        {
            return _instance ?? 
                  (_instance = new HttpClientService());
        }
    }
}

 

So the setting up of the HttpClientHandler property happens in the each Native level’s execution start up point.

On Android: MainActivity.cs

protected override void OnCreate(Bundle savedInstanceState)
{
    ...
    
    var androidClientHandler = new HttpClientHandler();
    Services.HttpClientService.HttpClientHandler =               
                                     androidClientHandler;
    
    ...
}

 

On iOS: AppDelegate.cs

public override bool FinishedLaunching(UIApplication app, NSDictionary options)
{
    ...
    
    var iosClientHandler = new NSUrlSessionHandler();
    Services.HttpClientService.HttpClientHandler = iosClientHandler;

    ...
}

 

On Windows (UWP): MainPage.xaml.cs

public MainPage()
{
    ...

    var uwpClientHandler = new WinHttpHandler();
    Services.HttpClientService.HttpClientHandler = uwpClientHandler;

    ...
}

 

That’s it for the set up, then let’s use it in Xamarin.Forms code:

var result = await HttpClientService.Instance.
		HttpClient.GetAsync("https://google.com/");

 

Now this should provide you with a Xamarin.Forms Solution allowing you to be able to access all the Properties and Behaviors of Native HttpClientHandlers!

Yay! Access in Code!

So the whole point of access these Native HttpClientHandlers in code was to be able to customize their settings and behaviors according to our requirements eh! 😀

Go ahead and access those properties and behaviors that you wish to use…

Here’s me demonstrate a simple scenario, how to override HTTPS Certificate Validation while using our Native HttpClientHandlers!

Full gist: https://gist.github.com/UdaraAlwis/0787f74796d22c294b91be81ff162347

Things Keep in mind!

So when you’re accessing the Native HttpClientHandlers in code there are some things you need to absolutely keep in your mind, to make sure the performance and security is not compromised.

– Custom bits, only Native level!

All the custom configuration that you need to do should be done in Native Xamarin level code, accordingly to native properties and behaviors.

– One time init() only!

You should instantiate your Native HttpClientHandler instances from Native level only once, and they shouldn’t be altered later for consistency during run time across your app.

– HttpMessageHandler, keep it as it is!

Keep the HttpMessageHandler instance that we up-cast from the Native HttpClientHandler instances as it is after instantiation, to make sure you’re not overriding any native properties and behaviors that we set up or inherited prior.

– Release Build, watch out!

When you’re using the Xamarin Platform specific Project Settings, make sure those settings are propagated to Release mode as well. In .csproj file has separate configurations for Debug and Release build configurations, so make sure keep an eye out for those configuration during Release builds as well.

Conclusion

Whenever you need to use the HttpClientHandler along side HttpClient, in your Xamarin.Forms or Native Xamarin Apps, its best to use the Native HttpClientHandler. This can be easily configured in each Native Project Settings or we can even instantiate them in code to be used across our Xamarin.Forms app environment as I’ve explained in this article.

I have shared the demo app code in my github as usual: github.com/XFNativeHttpClientHandler

Well that’s it! 😉

Share the love! Cheers!

Prepping your Xamarin.Forms App for Penetration Testing!

Let’s make sure your Xamarin.Forms App is ready for Penetration Testing, or widely known as PEN Testing! Focused on the Network Communication Layer, so that we can have a peace of mind for ourselves without being annoyed by our QA and Security Analysis team! 😉 lol

In any Mobile App Development project, we need to thoroughly test our Mobile Apps for vulnerabilities and security of user data. That is why these penetration testing processes are very important, we need to make sure that we deliver a mobile application as hardened and safe guarded as possible for our Users.

Now this post is not about securing or hardening the security of your mobile app, but rather how to prepare your Xamarin.Forms built app for QA and PEN Testing procedures.

But why, Xamarin.Forms?

Xamarin.Forms does an incredible job at producing a almost native-like level Mobile Application at the end of development. But given the unique nature of Xamarin.Forms, the .NET framework that we work with, sometimes developers take it for granted, giving all the responsibility to the framework, and we miss some bits that we need to pay attention to in oppose to native mobile development.

We need to make sure our App is compatible with the QA and PEN Testing procedures. Most of the QA and PEN testing revolves around the Native Mobile App environment. But sometimes those typical native mobile app testing processes aren’t compatible with what we work on out of the box of default .NET builds of Xamarin.Forms!

PEN Testing of a Mobile App…

Now there are many different kinds of QA procedures and PEN Test cases, such as local DB analysis, MiTM packet analysis, etc. In order to support those different PEN Test procedures, some times we need to provide separate builds with different configurations of your app to our PEN Test team. Such as disabling SSL Pinning in the app so that they can execute MiTM packet analysis testing on our app, and there could be many different scenarios as such.

So I’m going to share with you some of the important key points that you need to make sure you have configured in your Xamarin.Forms project, specifically in your Network Communication Layer and for some of those custom builds that you might have to provide for the PEN Testing process.

HttpClient Handler setup..

While Xamarin does provide a full fledged Managed HttpClient and Handler, it is best to set up the HattpClient’s handlers to the device native handlers. This will make sure better performance and better native system level security for your app.

On your Xamarin.Forms project solution, go to the Android project node -> Properties -> Android Options -> Click “Advanced” button and take a look at HttpClient implementation and SSL/TLS implementation.

Make sure to set them up as above using the native Android handler, and Default (Native TLS 1.2+) Transport Layer Security for all the web calls. This will make sure all our web endpoint calls will be handled by those configurations which are best suited for performance and security of the native android system.

Then for the iOS, On your Xamarin.Forms project solution, go to the iOS project node -> Properties -> iOS Build and take a look at HttpClient implementation.

Make sure its set to NSUrlSession handler, which will provide your iOS app with native iOS level security and better performance for web endpoint calls. Also this means your app won’t support devices before iOS version 7, so better check your app requirements as well.

HttpClient setup in Xamarin.Forms!

It is very crucial that you imperilment the use of HttpClient in your Xamarin.Forms app properly with performance and security in mind. It would be best to register the instance of HttpClient as a Singleton, and refer to that singular instance for all your web endpoint calls. This will not only make it easy for debugging, also easy for configuring your API/Web endpoint execution layer’s implementation.

And set up a HttpClientHandler to be passed into your HttpClient instance during the instantiation, so that we can include all the custom configuration easily.

Unless its a must, make sure to use the Native HttpClientHandlers for your HttpClient, which will increase the performance and native security features for your app.

  • Android: AndroidClientHandler
  • iOS: NSUrlSessionHandler
  • UWP: WinHttpHandler

Instead using the .NET Managed HttpClientHandler, use the above instances mapped up to your Xamarin.Forms shared environment. Here’s something that might be useful: Xamarin and the HttpClient For iOS, Android and Windows

Do not re-instantiate the same HttpClientHandler nor HttpClient instance during run time and keep those different configuration separately for each HttpClient by registering multiple types with a pre-defined use case. Such as AuthClient for handling authentication and ApiClient for normal endpoint calls.

Although there are third party HttpClient libraries such as ModernHttpClient, that provide better features for these specific scenarios, so you could even try one of them! 😉

Disable SSL Certificate Validation..

In case if you needed to disable HTTPS / SSL Certificate validation for your PEN Test procedures such as Man-in-The-Middle packet trace analysis, then we can easily disable this by overriding the Certificate validation execution in the HttpClientHandler and assigning that to HttpClient.

var handler = new HttpClientHandler();
handler.ServerCertificateCustomValidationCallback =
	(message, certificate, chain, sslPolicyErrors) => true;

HttpClient = new HttpClient(handler);

 

The above applies of course if you have set up Managed HttpClientHandler in your Xamarin.Android and Xamarin.iOS settings instead of using the native handlers.

If you have set up your projects with Native HttpClientHandler then you can easily disable HTTPS Certificate validation by following ways.

For Android, create a Custom derived implementation of AndroidClientHandler as follows,

public class CustomAndroidClientHandler : AndroidClientHandler
{
	protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
	{
		request.Version = new System.Version(2, 0);
		return await base.SendAsync(request, cancellationToken);
	}

	protected override SSLSocketFactory ConfigureCustomSSLSocketFactory(HttpsURLConnection connection)
	{
		return SSLCertificateSocketFactory.GetInsecure(0, null);
	}

	protected override IHostnameVerifier GetSSLHostnameVerifier(HttpsURLConnection connection)
	{
		return new BypassHostnameVerifier();
	}
}

internal class BypassHostnameVerifier : Java.Lang.Object, IHostnameVerifier
{
	public bool Verify(string hostname, ISSLSession session)
	{
		return true;
	}
}

Based on: https://nicksnettravels.builttoroam.com/android-certificates/

for iOS, subscribe to TrustOverride and return true to override certificate validation.

var iosClientHandler = new NSUrlSessionHandler();
iosClientHandler.TrustOverride += (sender, trust) =>
{
	return true;
};

 

For UWP: subscribe to ServerCertificateValidationCallback and return true to override certificate validation.

var uwpClientHandler = new WinHttpHandler() 
{ 
	ServerCertificateValidationCallback = 
		(message, certificate2, arg3, arg4) =>
		{
			return true;
		}
};

 

As you can see in all the snippets above we’re overriding HTTPS Certificate Validation process manually. Now this is not a build to be pushed for Production, make sure to produce this build as a Test only build for PEN testing. So I would suggest keep this configuration in a separate branch build and opt back to the main branch for production release.

Enable Self-Signed SSL Certificates..

Instead of disabling entire SSL Certificate validation process, we could narrow down the override to a certain SSL Certificates, such as a Self-Signed Certificate endpoints that our PEN Testers might be using.

Although there are many ways to do this, basically we include the given self-signed certificate data in the app’s configuration, or override the validation with it’s key. I would recommend going into the following tutorials for it hence it covers a wide aspect of it for both iOS and Android.

Self Signed iOS Certifcates and Certificate Pinning in a Xamarin.Forms application

Self Signed Android Certificates and Certificate Pinning in Xamarin.Forms

So kudos to nicksnettravels blog! 😉 They’ve got great stuff in there!

Enable non-HTTPS!

As you know by default Android (since Android P) and iOS platforms doesn’t allow insecure non-HTTPS calls to be made from our apps,

Now we might have to disable this during development until the back end server is TSL enabled or even for a PEN test case with a custom build.

Let’s disable this on Android by using android:networkSecurityConfig in your AndroidManifest.xml with a reference to the @xml/network_security_config which we’ll create next.

<manifest ... >
    <application
        android:networkSecurityConfig="@xml/network_security_config"
        ... >
        <!-- Place child elements of <application> element here. -->
    </application>
</manifest>

 

Add a new folder called “xml” in your Resources folder and add a new xml file with the name network_security_config.xml this will hold the key to disable or enable HTTPS connections restriction as you wish.

<?xml version="1.0" encoding="utf-8" ?>
<network-security-config>
  <domain-config cleartextTrafficPermitted="true" />
</network-security-config>

 

You can set cleartextTrafficPermitted to false later during production build.

And on iOS add the following configuration in the info.plist file.

<key>NSAppTransportSecurity</key>
<dict>
    <key>NSAllowsArbitraryLoads</key>
    <true/>
</dict>

 

Oh once again, make sure to disable this during PROD builds!

System Proxy Settings support!

Something to keep in mind is that you don’t need to worry about System Proxy settings as long as you’re using the Native HttpClientHandlers as they would by default use the system preferences under the hood, but if you’re using Managed .NET HttpClientHandlers then you need to handle the System native Proxy Settings.

You can do this by creating a Platform specific Service that will extract the System Proxy Settings, and you can use that when you’re instantiating HttpClientHanlder. This article provides a great example for it: HttpClient and Proxy

Is all good? 😉

Now before you ship out your build for the PEN test you can make sure everything is in place according to your specific requirements.

BadSSL (https://badssl.com/) is a great web tool to check whether your app is able to access non-https endpoints or self-signed certificate endpoints and so on based on your PEN Test requirement. You can call upon those test endpoints directly from your app to make sure they’re accessible or not.

Network monitoring tools like Fiddler and Charles Proxy, allows you to set up dummy local proxy servers that you can test with in order to make sure your app supports proxy communication or in that case App’s compatibility with using System proxy settings. You could even monitor the data streams going in and out of the app, and see if they’re properly secured with encryption.

So for this demo I prepared a little sample app which showcases the use of non-HTTPS, Self-Signed endpoints access, and Proxy settings reading capabilities. Check out below Android, iOS and UWP run times…

As you can see it’s able to go through all the defined scenarios I mentioned before. For this demo app I’m using all Native HttpClientHandlers, so I’m using the exact code snippets I’ve shared in this blog post. Now let me try to emulate some failure scenarios where its missing some configuration I shared in this post.

Full demo code: github.com/UdaraAlwis/XFPenTestPrepDemo

   

1st I’m emulating the instance where Self-Signed HTTPS endpoints unauthorized to execute as well as Non-HTTPS endpoints blocked by default System Security layer. 2nd one shows where the Self-Signed HTTPS is diabled but non-HTTPS endpoints allowed and so on to the 3rd scenario.

Well that’s it. Hope this helps you to configure your app properly with security in mind and provide builds for the PEN Test processes according to the requirements. 🙂

Share the love! Cheers! 😀