[Android] Fix the Setting Content of ContentView through style would crash on parent change

src/Controls/tests/TestCases.HostApp/Issues/Issue11812.cs

@@ -0,0 +1,65 @@
+using System.ComponentModel;
+using System.Runtime.CompilerServices;
+
+namespace Maui.Controls.Sample.Issues;
+
+[Issue(IssueTracker.Github, 11812, "Setting Content of ContentView through style would crash on parent change", PlatformAffected.Android)]
+public class Issue11812 : ContentPage
+{
+	ContentView _mainContentView;
+	public Issue11812()
+	{
+		var button = new Button
+		{
+			Text = "Add ContentView",
+			HorizontalOptions = LayoutOptions.Center,
+			AutomationId = "ChangeInnerContent"
+		};
+		button.Clicked += OnButtonClicked;
+
+		_mainContentView = new ContentView();
+		_mainContentView.Content = new Issue11812InnerContentView();
+
+		var layout = new VerticalStackLayout
+		{
+			Spacing = 25,
+			Padding = new Thickness(30, 0),
+			VerticalOptions = LayoutOptions.Center,
+			Children =
+			{
+				button,
+				_mainContentView
+			}
+		};
+
+		Content = layout;
+	}
+	private void OnButtonClicked(object sender, EventArgs e)
+	{
+		_mainContentView.Content = new Issue11812InnerContentView() { BackgroundColor = Colors.Red };
+	}
+}
+
+public class Issue11812InnerContentView : ContentView
+{
+	public Issue11812InnerContentView()
+	{
+		Application.Current.Resources ??= new ResourceDictionary();
+
+		if (!Application.Current.Resources.ContainsKey("SubContentStyle"))
+		{
+			Application.Current.Resources["SubContentStyle"] = new Style(typeof(ContentView))
+			{
+				Setters =
+			{
+				new Setter
+				{
+					Property = ContentView.ContentProperty,
+					Value = new Label { Text = "SubContent" }
+				}
+			}
+			};
+		}
+		Style = (Style)Application.Current.Resources["SubContentStyle"];
+	}
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue11812.cs

@@ -0,0 +1,23 @@
+#if TEST_FAILS_ON_WINDOWS // test fails on windows , see https://github.com/dotnet/maui/issues/29930
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues;
+
+public class Issue11812 : _IssuesUITest
+{
+	public Issue11812(TestDevice device) : base(device) { }
+
+	public override string Issue => "Setting Content of ContentView through style would crash on parent change";
+
+	[Test]
+	[Category(UITestCategories.Border)]
+	public void InnerContentViewShouldNotCrashWhenDynamicallyChange()
+	{
+		App.WaitForElement("ChangeInnerContent");
+		App.Tap("ChangeInnerContent");
+		App.WaitForElement("ChangeInnerContent");
+	}
+}
+#endif

src/Core/src/Handlers/Border/BorderHandler.Android.cs

@@ -42,7 +42,12 @@ static partial void UpdateContent(IBorderHandler handler)
 			handler.PlatformView.RemoveAllViews();
 
 			if (handler.VirtualView.PresentedContent is IView view)
-				handler.PlatformView.AddView(view.ToPlatform(handler.MauiContext));
+			{
+				var platformView = view.ToPlatform(handler.MauiContext);
+				// Ensure the view is detached from any existing parent before adding it
+				platformView.RemoveFromParent();
+				handler.PlatformView.AddView(platformView);
+			}
 		}
 
 		public static partial void MapHeight(IBorderHandler handler, IBorderView border)

src/Core/src/Handlers/Border/BorderHandler.iOS.cs

@@ -48,6 +48,7 @@ static partial void UpdateContent(IBorderHandler handler)
 			if (handler.VirtualView.PresentedContent is IView content)
 			{
 				var platformContent = content.ToPlatform(handler.MauiContext);
+				platformContent.RemoveFromSuperview();
 
 				// If the content is a UIScrollView, we need a container to handle masks and clip shapes effectively.
 				if (platformContent is UIScrollView)

src/Core/src/Handlers/ContentView/ContentViewHandler.Android.cs

@@ -39,7 +39,12 @@ static void UpdateContent(IContentViewHandler handler)
 			handler.PlatformView.RemoveAllViews();
 
 			if (handler.VirtualView.PresentedContent is IView view)
-				handler.PlatformView.AddView(view.ToPlatform(handler.MauiContext));
+			{
+				var platformView = view.ToPlatform(handler.MauiContext);
+				// Ensure the view is detached from any existing parent before adding it
+				platformView.RemoveFromParent();
+				handler.PlatformView.AddView(platformView);
+			}
 		}
 
 		public static partial void MapContent(IContentViewHandler handler, IContentView page)

src/Core/src/Handlers/ContentView/ContentViewHandler.iOS.cs

@@ -38,6 +38,7 @@ static void UpdateContent(IContentViewHandler handler)
 			if (handler.VirtualView.PresentedContent is IView view)
 			{
 				var platformView = view.ToPlatform(handler.MauiContext);
+				platformView.RemoveFromSuperview();
 				handler.PlatformView.AddSubview(platformView);
 
 				if (view.FlowDirection == FlowDirection.MatchParent)