fix: load XamlRoot RootElement in UnoIslands

src/Uno.UI.XamlHost.Skia.Wpf/UnoXamlHostBase.Layout.cs

@@ -26,7 +26,7 @@ protected override Size MeasureOverride(Size constraint)
 
 			if (IsXamlContentLoaded())
 			{
-				_xamlSource.Content.Measure(new Windows.Foundation.Size(constraint.Width, constraint.Height));
+				_xamlSource.XamlIsland.Measure(new Windows.Foundation.Size(constraint.Width, constraint.Height));
 				desiredSize.Width = _xamlSource.Content.DesiredSize.Width;
 				desiredSize.Height = _xamlSource.Content.DesiredSize.Height;
 			}
@@ -50,7 +50,7 @@ protected override Size ArrangeOverride(Size finalSize)
 				// set to 'Stretch'.  The UWP XAML content will be 0 in the stretch alignment direction
 				// until Arrange is called, and the UWP XAML content is expanded to fill the available space.
 				var finalRect = new Windows.Foundation.Rect(0, 0, finalSize.Width, finalSize.Height);
-				_xamlSource.Content.Arrange(finalRect);
+				_xamlSource.XamlIsland.Arrange(finalRect);
 			}
 
 			return base.ArrangeOverride(finalSize);
@@ -87,26 +87,5 @@ private void XamlContentSizeChanged(object sender, WUX.SizeChangedEventArgs e)
 		{
 			InvalidateMeasure();
 		}
-
-		private void OnSizeChanged(object sender, System.Windows.SizeChangedEventArgs e)
-		{
-			UpdateUnoSize();
-		}
-
-		//TODO: This is temporary workaround, should not be needed as per UWP islands. https://github.com/unoplatform/uno/issues/8978
-		//Might be some missing logic. Maybe not needed now after Arrange and Measure works with XamlIslandRoot
-		private void UpdateUnoSize()
-		{
-			if (IsXamlContentLoaded())
-			{
-				if (_xamlSource.GetVisualTreeRoot() is WUX.FrameworkElement element)
-				{
-					var width = ActualWidth;
-					var height = ActualHeight;
-					element.Width = width;
-					element.Height = height;
-				}
-			}
-		}
 	}
 }

src/Uno.UI.XamlHost.Skia.Wpf/UnoXamlHostBase.cs

@@ -116,8 +116,6 @@ public UnoXamlHostBase()
 
 			// Hook DesktopWindowXamlSource OnTakeFocus event for Focus processing
 			_xamlSource.TakeFocusRequested += OnTakeFocusRequested;
-
-			SizeChanged += OnSizeChanged;
 		}
 
 		/// <summary>
@@ -248,8 +246,6 @@ protected WUX.UIElement ChildInternal
 
 				// Fire updated event
 				ChildChanged?.Invoke(this, new EventArgs());
-
-				UpdateUnoSize();
 			}
 		}
 

src/Uno.UI/UI/Xaml/Hosting/DesktopWindowXamlSource.cs

@@ -3,6 +3,7 @@
 using System;
 using Uno.UI.Xaml.Islands;
 using Windows.Foundation;
+using Uno.UI.Xaml.Controls;
 using WinUICoreServices = global::Uno.UI.Xaml.Core.CoreServices;
 
 namespace Microsoft.UI.Xaml.Hosting;
@@ -49,7 +50,11 @@ public DesktopWindowXamlSource()
 	public UIElement Content
 	{
 		get => _xamlIsland.Content;
-		set => _xamlIsland.Content = value;
+		set
+		{
+			_xamlIsland.Content = value;
+			ContentManager.TryLoadRootVisual(_xamlIsland.XamlRoot!);
+		}
 	}
 
 	internal XamlIsland XamlIsland => _xamlIsland;

src/Uno.UI/UI/Xaml/Internal/Islands/XamlIsland.cs

@@ -27,8 +27,6 @@ public UIElement? Content
 			_contentManager.Content = value;
 
 			SetPublicRootVisual(value, null, null);
-
-			// TODO:MZ: Islands loading?
 		}
 	}