feat: Support for multiple XamlRoots

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

@@ -10,6 +10,7 @@
 using Uno.Foundation.Logging;
 using Uno.UI.Extensions;
 using Uno.UI.Xaml.Input;
+using Uno.UI.Xaml.Islands;
 using Windows.UI;
 using Windows.UI.Xaml;
 using Windows.UI.Xaml.Controls;
@@ -590,17 +591,15 @@ private void RemoveRoot(UIElement root)
 		[NotImplemented]
 		private static UIElement? GetXamlIslandRootForElement(DependencyObject? pObject)
 		{
-			return null;
-			//TODO Uno: XamlIslandRoot not needed for now.
 			//if (!pObject || !pObject->GetContext()->HasXamlIslands())
 			//{
 			//	return nullptr;
 			//}
-			//if (VisualTree * visualTree = GetForElementNoRef(pObject))
-			//{
-			//	return do_pointer_cast<CXamlIslandRoot>(visualTree->m_rootElement);
-			//}
-			//return null;
+			if (GetForElement(pObject) is VisualTree visualTree)
+			{
+				return visualTree.RootElement;
+			}
+			return null;
 		}
 
 		internal static VisualTree? GetForElement(DependencyObject? element, LookupOptions options = LookupOptions.WarningIfNotFound)
@@ -667,12 +666,11 @@ private void RemoveRoot(UIElement root)
 					}
 				}
 
-				//if (currentAncestor.GetTypeIndex() == KnownTypeIndex::XamlIsland)
-				//{
-				//	return static_cast<CXamlIslandRoot*>(currentAncestor)->GetVisualTreeNoRef();
-				//}
-				//else
-				if (currentAncestor is RootVisual rootVisual)
+				if (currentAncestor is XamlIslandRoot xamlIslandRoot)
+				{
+					return xamlIslandRoot.ContentRoot.VisualTree;
+				}
+				else if (currentAncestor is RootVisual rootVisual)
 				{
 					return rootVisual.AssociatedVisualTree;
 				}
@@ -773,9 +771,7 @@ internal XamlRoot GetOrCreateXamlRoot()
 		{
 			if (XamlRoot == null)
 			{
-				//TODO Uno: Our current implementation has only a single XAML root.
-				//In the future we may want to support multiple.
-				XamlRoot = XamlRoot.Current;
+				XamlRoot = new XamlRoot(this);
 			}
 
 			return XamlRoot;

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

@@ -2,34 +2,35 @@
 
 using System;
 using System.Collections.Generic;
+using Uno.UI.Xaml.Core;
 using Windows.Foundation;
 
-namespace Windows.UI.Xaml
+namespace Windows.UI.Xaml;
+
+/// <summary>
+/// Represents a tree of XAML content and information about the context in which it is hosted.
+/// </summary>
+/// <remarks>
+/// Effectively a public API wrapper around VisualTree.
+/// </remarks>
+public sealed partial class XamlRoot
 {
-	/// <summary>
-	/// Represents a tree of XAML content and information about the context in which it is hosted.
-	/// </summary>
-	/// <remarks>
-	/// Effectively a public API wrapper around VisualTree.
-	/// </remarks>
-	public sealed partial class XamlRoot
+	internal XamlRoot(VisualTree visualTree)
 	{
-		private XamlRoot() { }
-
-		internal static XamlRoot Current { get; } = new XamlRoot();
+		VisualTree = visualTree;
+	}
 
-		public event TypedEventHandler<XamlRoot, XamlRootChangedEventArgs>? Changed;
+	public event TypedEventHandler<XamlRoot, XamlRootChangedEventArgs>? Changed;
 
-		public UIElement? Content => Window.Current?.Content;
+	public UIElement? Content => Window.Current?.Content;
 
-		public Size Size => Content?.RenderSize ?? Size.Empty;
+	public Size Size => Content?.RenderSize ?? Size.Empty;
 
-		public double RasterizationScale
-			=> global::Windows.Graphics.Display.DisplayInformation.GetForCurrentView().RawPixelsPerViewPixel;
+	public double RasterizationScale
+		=> global::Windows.Graphics.Display.DisplayInformation.GetForCurrentView().RawPixelsPerViewPixel;
 
-		internal void NotifyChanged()
-		{
-			Changed?.Invoke(this, new XamlRootChangedEventArgs());
-		}
+	internal void NotifyChanged()
+	{
+		Changed?.Invoke(this, new XamlRootChangedEventArgs());
 	}
 }

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

@@ -1,12 +1,10 @@
-using DirectUI;
+#nullable enable
+
 using Uno.UI.Xaml.Core;
 
-namespace Windows.UI.Xaml
+namespace Windows.UI.Xaml;
+
+public sealed partial class XamlRoot
 {
-	public sealed partial class XamlRoot
-	{
-		//TODO Uno: This implementation does not match WinUI, but we currently support only
-		//a single XamlRoot and a single window. This will need to be adjusted later though.
-		internal VisualTree VisualTree => DXamlCore.Current.GetHandle().ContentRootCoordinator.CoreWindowContentRoot.VisualTree;
-	}
+	internal VisualTree VisualTree { get; set; }
 }