🚧 DRAFT: Correct ancestor XAML memory leak

Microsoft.Toolkit.Uwp.UI/Extensions/FrameworkElement/FrameworkElementExtensions.RelativeAncestor.cs

@@ -27,14 +27,14 @@ public static object GetAncestor(DependencyObject obj)
         /// <param name="value">FrameworkElement</param>
         public static void SetAncestor(DependencyObject obj, object value)
         {
-            obj.SetValue(AncestorProperty, value);
+            obj.SetValue(AncestorProperty, new WeakReference<object>(value));
         }
 
         /// <summary>
         /// Attached <see cref="DependencyProperty"/> for retrieving a parent <see cref="object"/> for the <see cref="AncestorProperty"/>
         /// </summary>
         public static readonly DependencyProperty AncestorProperty =
-            DependencyProperty.RegisterAttached("Ancestor", typeof(object), typeof(FrameworkElementExtensions), new PropertyMetadata(null));
+            DependencyProperty.RegisterAttached("Ancestor", typeof(WeakReference<object>), typeof(FrameworkElementExtensions), new PropertyMetadata(null));
 
         /// <summary>
         /// Gets the Type of Ancestor to look for from this element.

UnitTests/UnitTests.UWP/Extensions/Test_FrameworkElementExtensions.cs

@@ -0,0 +1,95 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using Microsoft.Toolkit.Uwp;
+using Microsoft.Toolkit.Uwp.UI;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using System.Threading.Tasks;
+using Windows.UI.Xaml.Controls;
+using Windows.UI.Xaml.Markup;
+
+namespace UnitTests.Extensions
+{
+    [TestClass]
+    public class Test_FrameworkElementExtensions : VisualUITestBase
+    {
+        [TestCategory("FrameworkElementExtensions")]
+        [TestMethod]
+        public async Task Test_Ancestor_WeakReference()
+        {
+            // Need to sim loading the control, and not just load the XAML via XamlReader
+            await App.DispatcherQueue.EnqueueAsync(async () =>
+            {
+                var treeRoot = XamlReader.Load(
+           @"<Page
+                    xmlns=""http://schemas.microsoft.com/winfx/2006/xaml/presentation""
+                    xmlns:x=""http://schemas.microsoft.com/winfx/2006/xaml""
+                    xmlns:controls=""using:Microsoft.Toolkit.Uwp.UI.Controls""
+                    xmlns:ui=""using:Microsoft.Toolkit.Uwp.UI"">
+
+                    <Grid x:Name=""OuterGrid"" Width=""200"" Background=""Khaki"">
+                        <Button x:Name=""InnerButton"" ui:FrameworkElementExtensions.AncestorType=""Grid"" />
+                    </Grid>
+
+                </Page>") as Page;
+
+                Assert.IsNotNull(treeRoot, "Could not load XAML tree.");
+                await SetTestContentAsync(treeRoot);
+
+                // Need to simulate loading the control (and not just rely upon XamlReader.Load)
+                var frame = new Frame();
+                frame.Navigate(treeRoot.GetType());
+                Assert.IsInstanceOfType(frame.Content, typeof(Page));
+
+                var btn = treeRoot.FindChild("InnerButton") as Button;
+
+                Assert.IsNull(btn.Parent);
+
+                btn.SetValue(FrameworkElementExtensions.AncestorProperty, new object());
+
+                Assert.IsNull(btn.Parent);
+            });
+        }
+
+        [TestCategory("FrameworkElementExtensions")]
+        [TestMethod]
+        public async Task Test_Ancestor_WeakRef_UnloadGrid()
+        {
+            // Need to sim loading the control, and not just load the XAML via XamlReader
+            await App.DispatcherQueue.EnqueueAsync(async () =>
+            {
+                var treeRoot = XamlReader.Load(
+           @"<Page
+                    xmlns=""http://schemas.microsoft.com/winfx/2006/xaml/presentation""
+                    xmlns:x=""http://schemas.microsoft.com/winfx/2006/xaml""
+                    xmlns:controls=""using:Microsoft.Toolkit.Uwp.UI.Controls""
+                    xmlns:ui=""using:Microsoft.Toolkit.Uwp.UI"">
+
+                    <Grid x:Name=""OuterGrid"" Width=""200"" Background=""Khaki"">
+                        <Button x:Name=""InnerButton"" ui:FrameworkElementExtensions.AncestorType=""Grid"" />
+                    </Grid>
+
+                </Page>") as Page;
+
+                Assert.IsNotNull(treeRoot, "Could not load XAML tree.");
+                await SetTestContentAsync(treeRoot);
+
+                // Need to simulate loading the control (and not just rely upon XamlReader.Load)
+                var frame = new Frame();
+                frame.Navigate(treeRoot.GetType());
+                Assert.IsInstanceOfType(frame.Content, typeof(Page));
+
+                var grid = treeRoot.FindChild("OuterGrid") as Grid;
+                var button = treeRoot.FindChild("InnerButton") as Button;
+
+                button.SetValue(FrameworkElementExtensions.AncestorProperty, new object());
+
+                treeRoot.Unloaded += (sender, e) =>
+                {
+                    Assert.AreEqual(grid, null);
+                };
+            });
+        }
+    }
+}

UnitTests/UnitTests.UWP/UnitTests.UWP.csproj

@@ -165,6 +165,7 @@
     <Compile Include="Converters\Test_StringFormatConverter.cs" />
     <Compile Include="Converters\Test_TypeToObjectConverter.cs" />
     <Compile Include="Extensions\Helpers\ObjectWithNullableBoolProperty.cs" />
+    <Compile Include="Extensions\Test_FrameworkElementExtensions.cs" />
     <Compile Include="Extensions\Test_StringExtensions.cs" />
     <Compile Include="Extensions\Test_UIElementExtensions_Coordinates.cs" />
     <Compile Include="Extensions\Test_VisualTreeExtensions.cs" />