feat(frameworkelement): Add VisualTreeHelper.AdaptNative()/TryAdaptNa…

…tive()

These methods support adding a native view (on Android, iOS, and MacOS) to Uno's visual tree where an instance of type UIElement is expected.

src/Uno.UI/UI/Xaml/Media/VisualTreeHelper.cs

@@ -20,7 +20,7 @@
 using _ViewGroup = AppKit.NSView;
 #elif XAMARIN_ANDROID
 using _ViewGroup = Android.Views.ViewGroup;
-using _View = Android.Views.ViewGroup;
+using _View = Android.Views.View;
 #else
 using _View = System.Object;
 #endif
@@ -58,15 +58,15 @@ public static IEnumerable<UIElement> FindElementsInHostCoordinates(Point interse
 		{
 			if (subtree != null)
 			{
-				if(IsElementIntersecting(intersectingPoint, subtree))
+				if (IsElementIntersecting(intersectingPoint, subtree))
 				{
 					yield return subtree;
 				}
 
 				foreach (var child in subtree.GetChildren().OfType<UIElement>())
 				{
 					var canTest = includeAllElements
-						|| ( child.IsHitTestVisible && child.IsViewHit());
+						|| (child.IsHitTestVisible && child.IsViewHit());
 
 					if (child is UIElement uiElement && canTest)
 					{
@@ -139,7 +139,7 @@ public static IReadOnlyList<Popup> GetOpenPopups(Window window)
 		public static DependencyObject GetParent(DependencyObject reference)
 		{
 #if XAMARIN
-			return (reference as _View)?
+			return (reference as _ViewGroup)?
 				.FindFirstParent<DependencyObject>();
 #else
 			return reference.GetParent() as DependencyObject;
@@ -153,5 +153,44 @@ internal static void CloseAllPopups()
 				popup.IsOpen = false;
 			}
 		}
+
+		/// <summary>
+		/// Adapts a native view by wrapping it in a <see cref="FrameworkElement"/> container so that it can be added to the managed visual tree.
+		/// </summary>
+		/// <remarks>
+		/// This method is present to support adding native view types on Android, iOS and MacOS to Uno's visual tree.
+		///
+		/// Calling it with a type that's already a <see cref="FrameworkElement"/> will throw an <see cref="InvalidOperationException"/>.
+		/// If there's a possibility that the wrapped type may be a <see cref="FrameworkElement"/>, use <see cref="TryAdaptNative(_View)"/>
+		/// instead.
+		/// </remarks>
+		public static FrameworkElement AdaptNative(_View nativeView)
+		{
+			if (nativeView is FrameworkElement)
+			{
+				throw new InvalidOperationException($"{nameof(AdaptNative)}() should only be called for non-{nameof(FrameworkElement)} native views." +
+					$"Use {nameof(TryAdaptNative)} if it's not known whether view will be native.");
+			}
+
+			return new ContentPresenter
+			{
+				Content = nativeView
+			};
+		}
+
+		/// <summary>
+		/// Adapts a native view by wrapping it in a <see cref="FrameworkElement"/> container so that it can be added to the managed visual tree.
+		///
+		/// This method is safe to call for any view. If <paramref name="view"/> is a <see cref="FrameworkElement"/>, it will simply be returned unmodified.
+		/// </summary>
+		public static FrameworkElement TryAdaptNative(_View view)
+		{
+			if (view is FrameworkElement fe)
+			{
+				return fe;
+			}
+
+			return AdaptNative(view);
+		}
 	}
 }