fix: Make Uno islands ContentIsland compatible with smooth resize

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

@@ -5,7 +5,9 @@
 
 using System;
 using System.Windows;
+using Microsoft.UI.Xaml.Hosting;
 using Uno.UI.XamlHost.Extensions;
+using Windows.Security.Cryptography.Certificates;
 using WUX = Microsoft.UI.Xaml;
 
 namespace Uno.UI.XamlHost.Skia.Wpf
@@ -46,6 +48,7 @@ protected override Size ArrangeOverride(Size finalSize)
 		{
 			if (IsXamlContentLoaded())
 			{
+				UpdateUnoSize(finalSize);
 				// Arrange is required to support HorizontalAlignment and VerticalAlignment properties
 				// 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.
@@ -62,18 +65,18 @@ protected override Size ArrangeOverride(Size finalSize)
 		/// <returns>True if the Xaml content is properly loaded</returns>
 		private bool IsXamlContentLoaded()
 		{
-			if (_xamlSource.Content == null)
+			if (_xamlSource.Content is null ||
+				!(_xamlSource.XamlIsland.IsLoading || _xamlSource.XamlIsland.IsLoaded))
 			{
 				return false;
 			}
 
-			//TODO: What should be the parent? https://github.com/unoplatform/uno/issues/8978
-			//if (WUX.Media.VisualTreeHelper.GetParent(_xamlSource.Content) == null)
-			//{
-			//    // If there's no parent to this content, it's not "live" or "loaded" in the tree yet.
-			//    // Performing a measure or arrange in this state may cause unexpected results.
-			//    return false;
-			//}
+			if (WUX.Media.VisualTreeHelper.GetParent(_xamlSource.Content) is null)
+			{
+				// If there's no parent to this content, it's not "live" or "loaded" in the tree yet.
+				// Performing a measure or arrange in this state may cause unexpected results.
+				return false;
+			}
 
 			return true;
 		}
@@ -90,21 +93,19 @@ private void XamlContentSizeChanged(object sender, WUX.SizeChangedEventArgs e)
 
 		private void OnSizeChanged(object sender, System.Windows.SizeChangedEventArgs e)
 		{
-			UpdateUnoSize();
+			UpdateUnoSize(e.NewSize);
 		}
 
 		//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()
+		private void UpdateUnoSize(Size newSize)
 		{
 			if (IsXamlContentLoaded())
 			{
-				if (_xamlSource.GetVisualTreeRoot() is WUX.FrameworkElement element)
+				if (_xamlSource?.XamlIsland is { } island)
 				{
-					var width = ActualWidth;
-					var height = ActualHeight;
-					element.Width = width;
-					element.Height = height;
+					island.Width = newSize.Width;
+					island.Height = newSize.Height;
 				}
 			}
 		}

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

@@ -10,6 +10,7 @@
 using WpfControl = global::System.Windows.Controls.Control;
 using WUX = Microsoft.UI.Xaml;
 using Uno.UI.Xaml.Controls;
+using Microsoft.UI.Content;
 
 namespace Uno.UI.XamlHost.Skia.Wpf
 {
@@ -249,8 +250,6 @@ protected WUX.UIElement ChildInternal
 
 				// Fire updated event
 				ChildChanged?.Invoke(this, new EventArgs());
-
-				UpdateUnoSize();
 			}
 		}
 
@@ -282,6 +281,7 @@ public object GetUwpInternalObject()
 		public bool IsDisposed { get; private set; }
 
 		private System.Windows.Window _parentWindow;
+		private ContentIsland _contentIsland;
 
 		//     /// <summary>
 		//     /// Creates <see cref="WUX.Application" /> object, wrapped <see cref="WUX.Hosting.DesktopWindowXamlSource" /> instance; creates and
@@ -325,7 +325,12 @@ protected virtual void SetContent()
 			if (_xamlSource != null)
 			{
 				_xamlSource.Content = _childInternal;
-				_xamlSource.XamlIsland.IsSiteVisible = true;
+				_contentIsland ??= new ContentIsland(_contentSite.View);
+				_xamlSource.XamlIsland.XamlRoot.VisualTree.ContentRoot.SetContentIsland(_contentIsland);
+
+				UpdateContentSiteVisible();
+				UpdateContentSiteScale();
+
 				TryLoadContent();
 			}
 		}
@@ -336,6 +341,7 @@ protected void TryLoadContent()
 			if (IsLoaded && _childInternal.XamlRoot is not null)
 			{
 				ContentManager.TryLoadRootVisual(_xamlSource.XamlIsland.XamlRoot);
+				InvalidateMeasure();
 			}
 		}
 

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

@@ -1,16 +1,18 @@
 #nullable enable
 
 using System.ComponentModel;
+using System.Windows;
 using System.Windows.Media;
-using WinUI = Microsoft.UI.Xaml;
-using WpfCanvas = global::System.Windows.Controls.Canvas;
-using Uno.UI.Runtime.Skia.Wpf.Rendering;
-using Uno.UI.XamlHost.Extensions;
-using Uno.UI.Runtime.Skia.Wpf.Hosting;
-using Uno.UI.Runtime.Skia.Wpf.Extensions;
+using Microsoft.UI.Content;
 using Uno.UI.Hosting;
 using Uno.UI.Runtime.Skia.Wpf;
-using Microsoft.UI.Content;
+using Uno.UI.Runtime.Skia.Wpf.Extensions;
+using Uno.UI.Runtime.Skia.Wpf.Hosting;
+using Uno.UI.Runtime.Skia.Wpf.Rendering;
+using Uno.UI.XamlHost.Extensions;
+using WinUI = Microsoft.UI.Xaml;
+using WpfCanvas = global::System.Windows.Controls.Canvas;
+using WpfWindow = global::System.Windows.Window;
 
 namespace Uno.UI.XamlHost.Skia.Wpf;
 
@@ -24,6 +26,8 @@ partial class UnoXamlHostBase : IWpfXamlRootHost
 	private WpfCanvas _nativeOverlayLayer;
 	private IWpfRenderer _renderer;
 	private Microsoft.UI.Xaml.UIElement? _rootElement;
+	private ContentSite _contentSite;
+	private WpfWindow? _window;
 
 	/// <summary>
 	/// Gets or sets the current Skia Render surface type.
@@ -43,11 +47,52 @@ public bool IgnorePixelScaling
 
 	private void InitializeHost()
 	{
+		_contentSite ??= new ContentSite();
+
+		this.IsVisibleChanged += (s, e) =>
+		{
+			UpdateContentSiteVisible();
+		};
+		this.Loaded += (s, e) =>
+		{
+			_window = WpfWindow.GetWindow(this);
+
+			if (_window is not null)
+			{
+				_window.DpiChanged += OnWindowDpiChanged;
+			}
+		};
+
+		this.Unloaded += (s, e) =>
+		{
+			if (_window is null)
+			{
+				return;
+			}
+
+			_window.DpiChanged -= OnWindowDpiChanged;
+			_window = null;
+		};
+
 		WpfExtensionsRegistrar.Register();
 
 		_designMode = DesignerProperties.GetIsInDesignMode(this);
 	}
 
+	private void UpdateContentSiteVisible()
+	{
+		_contentSite.IsSiteVisible = IsLoaded && IsVisible;
+		RaiseContentIslandStateChanged(ContentIslandStateChangedEventArgs.SiteVisibleChange);
+	}
+
+	private void OnWindowDpiChanged(object sender, DpiChangedEventArgs e) => UpdateContentSiteScale();
+
+	private void UpdateContentSiteScale()
+	{
+		_contentSite.ParentScale = (float)VisualTreeHelper.GetDpi(this).DpiScaleX;
+		RaiseContentIslandStateChanged(ContentIslandStateChangedEventArgs.RasterizationScaleChange);
+	}
+
 	protected override void OnRender(DrawingContext drawingContext)
 	{
 		base.OnRender(drawingContext);
@@ -78,4 +123,9 @@ void IXamlRootHost.InvalidateRender()
 	bool IWpfXamlRootHost.IgnorePixelScaling => IgnorePixelScaling;
 
 	RenderSurfaceType? IWpfXamlRootHost.RenderSurfaceType => RenderSurfaceType;
+
+	private void RaiseContentIslandStateChanged(ContentIslandStateChangedEventArgs args)
+	{
+		_contentIsland?.RaiseStateChanged(args);
+	}
 }