feat: Find associated VisualTree and XamlRoot for multiple roots

src/Uno.UI.Runtime.Skia.Wpf/Islands/UnoXamlHost.host.cs

@@ -66,9 +66,7 @@ private void InitializeHost()
 		}
 
 		protected override void OnRender(DrawingContext drawingContext)
-		{
-			base.OnRender(drawingContext);
-
+		{			
 			if (!IsXamlContentLoaded())
 			{
 				return;
@@ -133,12 +131,18 @@ protected override void OnRender(DrawingContext drawingContext)
 				{
 					WinUI.Window.Current.Compositor.RenderVisual(surface, ChildInternal.Visual);
 				}
+				surface.Canvas.Flush();
 			}
 
 			// draw the bitmap to the screen
-			_bitmap.AddDirtyRect(new Int32Rect(0, 0, width, height));
+			_bitmap.AddDirtyRect(new Int32Rect(0, 0, _bitmap.PixelWidth, _bitmap.PixelHeight));			
 			_bitmap.Unlock();
+
+
 			drawingContext.DrawImage(_bitmap, new Rect(0, 0, ActualWidth, ActualHeight));
+			drawingContext.DrawEllipse(Brushes.Blue, null, new Point(10, 10), 10, 10);
 		}
+
+		private Random _randomizer = new Random();
 	}
 }

src/Uno.UI.Runtime.Skia.Wpf/Islands/UnoXamlHostBase.cs

@@ -176,6 +176,7 @@ protected WUX.UIElement ChildInternal
 				if (currentRoot != null)
 				{
 					currentRoot.SizeChanged -= XamlContentSizeChanged;
+					currentRoot.XamlRoot.InvalidateRender -= XamlRoot_InvalidateRender;
 				}
 
 				_childInternal = value;
@@ -187,6 +188,7 @@ protected WUX.UIElement ChildInternal
 					// If XAML content has changed, check XAML size
 					// to determine if UnoXamlHost needs to re-run layout.
 					frameworkElement.SizeChanged += XamlContentSizeChanged;
+					frameworkElement.XamlRoot.InvalidateRender += XamlRoot_InvalidateRender;
 				}
 
 				OnChildChanged();
@@ -196,6 +198,12 @@ protected WUX.UIElement ChildInternal
 			}
 		}
 
+		private void XamlRoot_InvalidateRender()
+		{
+			//InvalidateOverlays();
+			InvalidateVisual();
+		}
+
 		/// <summary>
 		/// Called when the property <seealso cref="ChildInternal"/> has changed.
 		/// </summary>

src/Uno.UI.Runtime.Skia.Wpf/WpfIslandsHost.cs

@@ -96,12 +96,6 @@ void CreateApp(WinUI.ApplicationInitializationCallbackParams _)
 
 			WinUI.Application.Start(CreateApp, args);
 
-			WinUI.Window.InvalidateRender += () =>
-			{
-				InvalidateOverlays();
-				InvalidateVisual();
-			};
-
 			WpfApplication.Current.Activated += Current_Activated;
 			WpfApplication.Current.Deactivated += Current_Deactivated;
 			WpfApplication.Current.MainWindow.StateChanged += MainWindow_StateChanged;

src/Uno.UI.RuntimeTests/MUX/Helpers/FlyoutHelper.cs

@@ -11,12 +11,12 @@ namespace Uno.UI.RuntimeTests.MUX.Helpers
 {
 	internal static class FlyoutHelper
 	{
-		public static FrameworkElement GetOpenFlyoutPresenter()
+		public static FrameworkElement GetOpenFlyoutPresenter(XamlRoot xamlRoot)
 		{
 #if NETFX_CORE
 			var popups = VisualTreeHelper.GetOpenPopups(Window.Current);
 #else
-			var popups = VisualTreeHelper.GetOpenPopupsForXamlRoot(XamlRoot.Current);
+			var popups = VisualTreeHelper.GetOpenPopupsForXamlRoot(xamlRoot);
 #endif
 			if (popups.Count != 1)
 			{

src/Uno.UI.RuntimeTests/Tests/Windows_UI_Xaml_Controls/DatePickerIntegrationTests.cs

@@ -750,7 +750,7 @@ await RunOnUIThread.ExecuteAsync(() =>
 #else
 				var flyoutPopup = VisualTreeHelper.GetOpenPopupsForXamlRoot(datePicker.XamlRoot)[0];
 #endif
-				var datepickerFlyoutPresenter = GetDatePickerFlyoutPresenter();
+				var datepickerFlyoutPresenter = GetDatePickerFlyoutPresenter(datePicker.XamlRoot);
 
 				// The flyout popup, the flyout presenter and the button should have an RTL flow direction.
 				// The DatePicker itself should remain in LTR flow direction.
@@ -1096,9 +1096,9 @@ await RunOnUIThread.ExecuteAsync(() =>
 			});
 		}
 
-		private DatePickerFlyoutPresenter GetDatePickerFlyoutPresenter()
+		private DatePickerFlyoutPresenter GetDatePickerFlyoutPresenter(XamlRoot xamlRoot)
 		{
-			return FlyoutHelper.GetOpenFlyoutPresenter() as DatePickerFlyoutPresenter;
+			return FlyoutHelper.GetOpenFlyoutPresenter(xamlRoot) as DatePickerFlyoutPresenter;
 		}
 
 		private void VerifyDatesAreEqual(Calendar expected, DateTimeOffset actual)

src/Uno.UI/UI/Xaml/Internal/VisualTree.cs

@@ -675,22 +675,23 @@ private void RemoveRoot(UIElement root)
 					return rootVisual.AssociatedVisualTree;
 				}
 
+				DependencyObject? nextAncestor = null;
 				//TODO Uno: Uncomment and implement
-				//DependencyObject? nextAncestor = null;
-				//if (currentAncestor.DoesAllowMultipleAssociation() && currentAncestor.GetParentCount() > 1)
-				//{
-				//	// We cannot travese up a tree through a multiply associated element.  Our goal is to support DOs being
-				//	// shared between XAML trees.  We've seen cases where we traverse up the tree through CSetter objects,
-				//	// so for now we allow the traversal if there's one unique parent.  TODO: This could be fragile?  Allowing
-				//	// the traversal to happen when the parent count is 1 means that if this element gets another parent later,
-				//	// we're now in an inconsistent state.
-				//	// Bug 19548424: Investigate places where an element entering the tree doesn't have a unique VisualTree ptr
-				//}
-				//else
-				//{
-				//	nextAncestor = currentAncestor.GetParentInternal(false /* public parent only */);
-				//}
+				if (false)//currentAncestor.DoesAllowMultipleAssociation() && currentAncestor.GetParentCount() > 1)
+				{
+					// We cannot travese up a tree through a multiply associated element.  Our goal is to support DOs being
+					// shared between XAML trees.  We've seen cases where we traverse up the tree through CSetter objects,
+					// so for now we allow the traversal if there's one unique parent.  TODO: This could be fragile?  Allowing
+					// the traversal to happen when the parent count is 1 means that if this element gets another parent later,
+					// we're now in an inconsistent state.
+					// Bug 19548424: Investigate places where an element entering the tree doesn't have a unique VisualTree ptr
+				}
+				else
+				{
+					nextAncestor = currentAncestor.GetParentInternal(false /* public parent only */);
+				}
 
+				//TODO Uno: Uncomment and implement
 				////
 				//// We have a few tricks to figure out which VisualTree an element may be associated with.
 				//// There is now a cached weak VisualTree pointer on each DO that we update when we do a live
@@ -743,7 +744,7 @@ private void RemoveRoot(UIElement root)
 				//	}
 				//}
 
-				//currentAncestor = nextAncestor;
+				currentAncestor = nextAncestor;
 			}
 			if (result == null)
 			{

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

@@ -188,12 +188,12 @@ private static IReadOnlyList<Popup> GetOpenFlyoutPopups()
 
 		public static IReadOnlyList<Popup> GetOpenPopupsForXamlRoot(XamlRoot xamlRoot)
 		{
-			if (xamlRoot == XamlRoot.Current)
+			if (xamlRoot == Window.Current.RootElement.XamlRoot)
 			{
 				return GetOpenPopups(Window.Current);
 			}
 
-			return new Popup[0];
+			return Array.Empty<Popup>();
 		}
 
 

src/Uno.UI/UI/Xaml/UIElement.Layout.netstd.cs

@@ -43,7 +43,7 @@ public void InvalidateMeasure()
 				(this.GetParent() as UIElement)?.InvalidateMeasure();
 				if (IsVisualTreeRoot)
 				{
-					Window.InvalidateMeasure(this);
+					XamlRoot.InvalidateMeasure();
 				}
 			}
 		}
@@ -70,7 +70,7 @@ internal void InvalidateParentMeasureDirtyPath()
 			}
 			else if (IsVisualTreeRoot)
 			{
-				Window.InvalidateMeasure(XamlRoot);
+				XamlRoot.InvalidateMeasure();
 			}
 		}
 
@@ -97,7 +97,7 @@ public void InvalidateArrange()
 				(this.GetParent() as UIElement)?.InvalidateArrange();
 				if (IsVisualTreeRoot)
 				{
-					Window.InvalidateArrange(this);
+					XamlRoot.InvalidateArrange();
 				}
 			}
 		}
@@ -124,7 +124,7 @@ private void InvalidateParentArrangeDirtyPath()
 			}
 			else if (IsVisualTreeRoot)
 			{
-				Window.InvalidateArrange(this);
+				XamlRoot.InvalidateArrange();
 			}
 		}
 

src/Uno.UI/UI/Xaml/UIElement.cs

@@ -48,7 +48,6 @@ private static readonly Dictionary<Type, RoutedEventFlag> ImplementedRoutedEvent
 		private static readonly Type[] _bringIntoViewRequestedArgs = new[] { typeof(BringIntoViewRequestedEventArgs) };
 
 		private readonly SerialDisposable _clipSubscription = new SerialDisposable();
-		private XamlRoot _xamlRoot = null;
 		private string _uid;
 		private WeakReference<VisualTree> _visualTreeWeakReference;
 
@@ -212,8 +211,31 @@ string IXUidProvider.Uid
 
 		public XamlRoot XamlRoot
 		{
-			get => _xamlRoot ?? XamlRoot.Current;
-			set => _xamlRoot = value;
+			get
+			{
+				var visualTree = VisualTree.GetForElement(this);
+				if (visualTree is not null)
+				{
+					var xamlRoot = visualTree.GetOrCreateXamlRoot();
+					return xamlRoot;
+				}
+
+				return null;
+			}
+			set
+			{
+				if (XamlRoot == value)
+				{
+					return;
+				}
+
+				if (XamlRoot is not null)
+				{
+					throw new InvalidOperationException("Cannot change XamlRoot for existing element");
+				}
+
+				// TODO:MZ: It should be possible to set XamlRoot when still null.
+			}
 		}
 
 		#region VirtualizationInformation

src/Uno.UI/UI/Xaml/Window.cs

@@ -91,6 +91,7 @@ public UIElement Content
 						oldRoot.SizeChanged -= RootSizeChanged;
 					}
 				}
+
 				if (value != null)
 				{
 					value.IsWindowRoot = true;
@@ -100,9 +101,10 @@ public UIElement Content
 
 				if (value is FrameworkElement newRoot)
 				{
-					newRoot.SizeChanged += RootSizeChanged;
+					newRoot.SizeChanged += RootSizeChanged;					
 				}
-				XamlRoot.Current.NotifyChanged();
+
+				(value?.XamlRoot ?? oldContent?.XamlRoot)?.NotifyChanged();
 			}
 		}
 
@@ -221,10 +223,7 @@ internal void OnVisibilityChanged(bool newVisibility)
 			}
 		}
 
-		private void RootSizeChanged(object sender, SizeChangedEventArgs args)
-		{
-			XamlRoot.Current.NotifyChanged();
-		}
+		private void RootSizeChanged(object sender, SizeChangedEventArgs args) => _rootVisual.XamlRoot.NotifyChanged();
 
 		private void RaiseSizeChanged(Windows.UI.Core.WindowSizeChangedEventArgs windowSizeChangedEventArgs)
 		{

src/Uno.UI/UI/Xaml/Window.skia.cs

@@ -33,6 +33,8 @@ public void Init()
 		{
 			Dispatcher = CoreDispatcher.Main;
 			CoreWindow = CoreWindow.GetOrCreateForCurrentThread();
+			InitDragAndDrop();
+		}		
 			CoreWindow.SetInvalidateRender(QueueInvalidateRender);
 
 			InitializeCommon();
@@ -95,6 +97,8 @@ private void InternalSetContent(UIElement content)
 					throw new InvalidOperationException("The root visual could not be created.");
 				}
 
+				CoreWindow.SetInvalidateRender(_rootVisual.XamlRoot.QueueInvalidateRender);
+
 				UIElement.LoadingRootElement(_rootVisual);
 
 				Compositor.RootVisual = _rootVisual.Visual;

src/Uno.UI/UI/Xaml/XamlRoot.cs

@@ -1,6 +1,7 @@
 #nullable enable
 
 using Uno.UI.Xaml.Core;
+using Uno.UI.Xaml.Islands;
 using Windows.Foundation;
 
 namespace Windows.UI.Xaml;
@@ -18,11 +19,52 @@ internal XamlRoot(VisualTree visualTree)
 		VisualTree = visualTree;
 	}
 
+	/// <summary>
+	/// Occurs when a property of XamlRoot has changed.
+	/// </summary>
 	public event TypedEventHandler<XamlRoot, XamlRootChangedEventArgs>? Changed;
 
-	public UIElement? Content => Window.Current?.Content;
+	public UIElement? Content => VisualTree.PublicRootVisual;
 
-	public Size Size => Content?.RenderSize ?? Size.Empty;
+	//TODO Uno specific: This is most likely not implemented here in MUX:
+	public Size Size
+	{
+		get
+		{
+			var rootElement = VisualTree.RootElement;
+			if (rootElement is RootVisual rootVisual)
+			{
+				//TODO:MZ: Support multiple windows!
+				return Window.Current.Bounds.Size;
+			}
+			else if (rootElement is XamlIslandRoot xamlIslandRoot)
+			{
+				return new Size(xamlIslandRoot.ActualSize.X, xamlIslandRoot.ActualSize.Y);
+			}
+
+			return default;
+		}
+	}
+
+	//TODO Uno specific: This is most likely not implemented here in MUX:
+	internal Rect Bounds
+	{
+		get
+		{
+			var rootElement = VisualTree.RootElement;
+			if (rootElement is RootVisual rootVisual)
+			{
+				//TODO:MZ: Support multiple windows!
+				return Window.Current.Bounds;
+			}
+			else if (rootElement is XamlIslandRoot xamlIslandRoot)
+			{
+				return new Rect(0, 0, xamlIslandRoot.ActualSize.X, xamlIslandRoot.ActualSize.Y);
+			}
+
+			return default;
+		}
+	}
 
 	public double RasterizationScale
 		=> global::Windows.Graphics.Display.DisplayInformation.GetForCurrentView().RawPixelsPerViewPixel;