[release/10.0.1xx-sr7] [Windows] Fix COMException when restoring a ScrollView as ContentPage.Content after swapping it out

src/Controls/tests/TestCases.HostApp/Issues/Issue35277.cs

@@ -0,0 +1,56 @@
+namespace Maui.Controls.Sample.Issues;
+
+[Issue(IssueTracker.Github, 35277, "COMException when restoring a page content after swapping it out", PlatformAffected.UWP)]
+public class Issue35277 : ContentPage
+{
+	ScrollView _originalScrollView;
+
+	public Issue35277()
+	{
+		var swapButton = new Button
+		{
+			Text = "Swap and Restore",
+			HorizontalOptions = LayoutOptions.Center,
+			AutomationId = "SwapAndRestoreButton"
+		};
+		swapButton.Clicked += OnSwapAndRestoreClicked;
+
+		_originalScrollView = new ScrollView
+		{
+			Content = new VerticalStackLayout
+			{
+				Spacing = 20,
+				VerticalOptions = LayoutOptions.Center,
+				Children =
+				{
+					swapButton,
+					new Label
+					{
+						Text = "Original Content",
+						HorizontalOptions = LayoutOptions.Center,
+						AutomationId = "OriginalLabel"
+					}
+				}
+			}
+		};
+
+		Content = _originalScrollView;
+	}
+
+	void OnSwapAndRestoreClicked(object sender, EventArgs e)
+	{
+		var savedScrollView = _originalScrollView;
+		Content = new Label
+		{
+			Text = "Temporary Content",
+			HorizontalOptions = LayoutOptions.Center,
+			VerticalOptions = LayoutOptions.Center,
+			AutomationId = "TemporaryLabel"
+		};
+
+		Microsoft.Maui.ApplicationModel.MainThread.BeginInvokeOnMainThread(() =>
+		{
+			Content = savedScrollView;
+		});
+	}
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue35277.cs

@@ -0,0 +1,22 @@
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues;
+
+public class Issue35277 : _IssuesUITest
+{
+	public Issue35277(TestDevice device) : base(device) { }
+
+	public override string Issue => "COMException when restoring a page content after swapping it out";
+
+	[Test]
+	[Category(UITestCategories.ScrollView)]
+	public void ScrollViewContentShouldRestoreWithoutCOMException()
+	{
+		App.WaitForElement("SwapAndRestoreButton");
+		App.Tap("SwapAndRestoreButton");
+		// If no COMException is thrown, the original ScrollView content (with the button) restores successfully
+		App.WaitForElement("SwapAndRestoreButton");
+	}
+}

src/Core/src/Handlers/ScrollView/ScrollViewHandler.Windows.cs

@@ -38,6 +38,12 @@ protected override void ConnectHandler(ScrollViewer platformView)
 
 		protected override void DisconnectHandler(ScrollViewer platformView)
 		{
+			// Cascade disconnect to the PresentedContent's handler. Without this, when the
+			// ScrollView is restored as ContentPage.Content after being swapped out, the
+			// PresentedContent's native view still has a stale parent (the old ContentPanel),
+			// causing a WinUI COM exception "Element already has a parent" (Issue #35277).
+			// Cascading here ensures ToPlatform() creates a fresh native view with no parent.
+			VirtualView?.PresentedContent?.Handler?.DisconnectHandler();
 			base.DisconnectHandler(platformView);
 			platformView.ViewChanged -= ViewChanged;
 		}
@@ -149,20 +155,20 @@ static void UpdateContentPanel(IScrollView scrollView, IScrollViewHandler handle
 				{
 					currentPaddingLayer.CachedChildren.Clear();
 				}
-				
+
 				return;
 			}
 
+			if (currentPaddingLayer is not null)
+			{
+				currentPaddingLayer.CachedChildren.Clear();
+			}
+
 			var nativeContent = scrollView.PresentedContent.ToPlatform(handler.MauiContext);
 
 			if (currentPaddingLayer is not null)
 			{
-				// Only update if content has changed or is missing
-				if (currentPaddingLayer.CachedChildren.Count == 0 || currentPaddingLayer.CachedChildren[0] != nativeContent)
-				{
-					currentPaddingLayer.CachedChildren.Clear();
-					currentPaddingLayer.CachedChildren.Add(nativeContent);
-				}
+				currentPaddingLayer.CachedChildren.Add(nativeContent);
 			}
 			else
 			{