native-views.md

uid
Uno.Development.NativeViews

Incorporating native views to the Uno visual tree

The Android, iOS, and macOS targets for Uno support the notion of a purely native view, that is not coming from Uno Platform but instead defined in a third-party library, via a Xamarin binding, or in the native framework itself. Since Uno's views are inheriting from the base native view type on these platforms, you can incorporate native views into your app's visual tree.

Adding native views in XAML

There's no special syntax required when adding native views in XAML, apart from platform conditionals to ensure that the XAML compiles for all platforms. Uno's XAML parser supplies the needed 'glue', including supplying common constructor parameters (such as the Context parameter on Android).

An example:

      ...
	  Background="{ThemeResource ApplicationPageBackgroundThemeBrush}"
	  xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
	  xmlns:android="http://uno.ui/android"
	  mc:Ignorable="d android">

	<StackPanel Margin="0,30,0,0">
		<TextBlock Text="Rating" />
		<android:Grid Background="Beige"
					  Width="200">
			<RatingBar />
		</android:Grid>
	</StackPanel>

Adding native views in code

Adding native views in C# code requires you to first 'wrap' the native view in a special UIElement, because 'container' elements like Panel and Border expect a child of type UIElement (as of Uno 3.0 and above). The recommended way to do this is with the VisualTreeHelper.AdaptNative() static method:

using Windows.UI.Xaml.Media

...

    var ratingBar = new Android.Widget.RatingBar(Uno.UI.ContextHelper.Current);
    var wrapped = VisualTreeHelper.AdaptNative(ratingBar);
    _myBorder.Child = wrapped;

Note that VisualTreeHelper.AdaptNative() will throw an exception if it receives a FrameworkElement. If you're in a context where you don't know if the view you want to display is actually a purely native view or a managed FrameworkElement type, you can use VisualTreeHelper.TryAdaptNative() instead.

Assigning a native view directly as the Content property of ContentPresenter or ContentControl is also supported (since Content is of type object).

Troubleshooting

Uno makes certain assumptions about native views when it displays them, which may not always hold (eg that SizeThatFits() is implemented on iOS). Here are some things to try if your view isn't displaying:

• check the documentation and ensure you're configuring the native control correctly.
• try setting a fixed Width and Height on the outer XAML container.
• try setting the dimensions of the native view via code-behind.

Adding JavaScript views in WebAssembly

On WebAssembly, integrating native JavaScript views is done differently. Read this guide to learn how.