Correctly propagate BindingContext to Border StrokeShape

src/Controls/samples/Controls.Sample/Pages/Core/BorderGalleries/BorderStyles.xaml

@@ -7,7 +7,7 @@
     <ContentPage.Resources>
         <ResourceDictionary>
 
-            <Style TargetType="Border">
+            <Style x:Key="BorderStyle" TargetType="Border">
                 <Setter Property="StrokeShape" Value="RoundRectangle 10,10,10,10"/>
                 <Setter Property="Stroke" Value="Red"/>
                 <Setter Property="StrokeThickness" Value="1"/>
@@ -16,13 +16,34 @@
                 <Setter Property="BackgroundColor" Value="Transparent"/>
             </Style>
 
+            <Style x:Key="StrokeShapeBindingParentBorderStyle" TargetType="Border">
+                <Setter Property="StrokeShape">
+                    <RoundRectangle 
+                        CornerRadius="{Binding Source={RelativeSource AncestorType={x:Type Border}}, Path=Width}" />
+                </Setter>
+                <Setter Property="Stroke" Value="Red"/>
+                <Setter Property="StrokeThickness" Value="1"/>
+                <Setter Property="HeightRequest" Value="55"/>
+                <Setter Property="Padding" Value="10"/>
+                <Setter Property="BackgroundColor" Value="Transparent"/>
+            </Style>
+
         </ResourceDictionary>
     </ContentPage.Resources>
     <ContentPage.Content>
         <StackLayout 
             Margin="12" 
             Spacing="12">
-            <Border />
+            <Label
+                Text="Default"
+                Style="{StaticResource Headline}"/>
+            <Border
+                Style="{StaticResource BorderStyle}"/>
+            <Label
+                Text="StrokeShape binded to Parent"
+                Style="{StaticResource Headline}"/>
+            <Border
+                Style="{StaticResource StrokeShapeBindingParentBorderStyle}"/>
         </StackLayout>
     </ContentPage.Content>
 </ContentPage>

src/Controls/src/Core/Border.cs

@@ -1,4 +1,5 @@
-using System.Collections.Generic;
+using System;
+using System.Collections.Generic;
 using System.Collections.ObjectModel;
 using System.Collections.Specialized;
 using System.Runtime.CompilerServices;
@@ -14,6 +15,10 @@ public class Border : View, IContentView, IBorderView, IPaddingElement
 		float[]? _strokeDashPattern;
 		ReadOnlyCollection<Element>? _logicalChildren;
 
+		WeakNotifyPropertyChangedProxy? _strokeShapeProxy = null;
+
+		~Border() => _strokeShapeProxy?.Unsubscribe();
+
 		internal ObservableCollection<Element> InternalChildren { get; } = new();
 
 		internal override IReadOnlyList<Element> LogicalChildrenInternal =>
@@ -37,7 +42,42 @@ public Thickness Padding
 		}
 
 		public static readonly BindableProperty StrokeShapeProperty =
-			BindableProperty.Create(nameof(StrokeShape), typeof(IShape), typeof(Border), new Rectangle());
+			BindableProperty.Create(nameof(StrokeShape), typeof(IShape), typeof(Border), new Rectangle(),
+				propertyChanging: (bindable, oldvalue, newvalue) =>
+				{
+					if (newvalue is not null)
+						(bindable as Border)?.StopNotifyingStrokeShapeChanges();
+				},
+				propertyChanged: (bindable, oldvalue, newvalue) =>
+				{
+					if (newvalue is not null)
+						(bindable as Border)?.NotifyStrokeShapeChanges();
+				});
+
+		void NotifyStrokeShapeChanges()
+		{
+			var strokeShape = StrokeShape;
+
+			if (strokeShape is VisualElement visualElement)
+			{
+				SetInheritedBindingContext(visualElement, BindingContext);
+				visualElement.Parent = this;
+				var proxy = _strokeShapeProxy ??= new();
+				proxy.Subscribe(visualElement, (sender, e) => OnPropertyChanged(nameof(StrokeShape)));
+			}
+		}
+
+		void StopNotifyingStrokeShapeChanges()
+		{
+			var strokeShape = StrokeShape;
+
+			if (strokeShape is VisualElement visualElement)
+			{
+				SetInheritedBindingContext(visualElement, null);
+				visualElement.Parent = null;
+				_strokeShapeProxy?.Unsubscribe();
+			}
+		}
 
 		public static readonly BindableProperty StrokeProperty =
 			BindableProperty.Create(nameof(Stroke), typeof(Brush), typeof(Border), null);

src/Controls/src/Core/Internals/WeakEventProxy.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Specialized;
+using System.ComponentModel;
 
 // NOTE: warning disabled for netstandard projects
 #pragma warning disable 0436
@@ -102,4 +103,53 @@ public override void Unsubscribe()
 			base.Unsubscribe();
 		}
 	}
+
+	/// <summary>
+	/// A "proxy" class for subscribing INotifyPropertyChanged via WeakReference.
+	/// General usage is to store this in a member variable and call Subscribe()/Unsubscribe() appropriately.
+	/// Your class should have a finalizer that calls Unsubscribe() to prevent WeakNotifyCollectionChangedProxy objects from leaking.
+	/// </summary>
+	class WeakNotifyPropertyChangedProxy : WeakEventProxy<INotifyPropertyChanged, PropertyChangedEventHandler>
+	{
+		public WeakNotifyPropertyChangedProxy() { }
+
+		public WeakNotifyPropertyChangedProxy(INotifyPropertyChanged source, PropertyChangedEventHandler handler)
+		{
+			Subscribe(source, handler);
+		}
+
+		void OnPropertyChanged(object? sender, PropertyChangedEventArgs e)
+		{
+			if (TryGetHandler(out var handler))
+			{
+				handler(sender, e);
+			}
+			else
+			{
+				Unsubscribe();
+			}
+		}
+
+		public override void Subscribe(INotifyPropertyChanged source, PropertyChangedEventHandler handler)
+		{
+			if (TryGetSource(out var s))
+			{
+				s.PropertyChanged -= OnPropertyChanged;
+			}
+
+			source.PropertyChanged += OnPropertyChanged;
+
+			base.Subscribe(source, handler);
+		}
+
+		public override void Unsubscribe()
+		{
+			if (TryGetSource(out var s))
+			{
+				s.PropertyChanged -= OnPropertyChanged;
+			}
+
+			base.Unsubscribe();
+		}
+	}
 }

src/Controls/src/Core/PublicAPI/net-android/PublicAPI.Unshipped.txt

@@ -1,5 +1,6 @@
 #nullable enable
 *REMOVED*override Microsoft.Maui.Controls.RefreshView.MeasureOverride(double widthConstraint, double heightConstraint) -> Microsoft.Maui.Graphics.Size
+Microsoft.Maui.Controls.Border.~Border() -> void
 Microsoft.Maui.Controls.Handlers.Compatibility.FrameRenderer.FrameRenderer(Android.Content.Context! context, Microsoft.Maui.IPropertyMapper! mapper) -> void
 Microsoft.Maui.Controls.Handlers.Compatibility.FrameRenderer.FrameRenderer(Android.Content.Context! context, Microsoft.Maui.IPropertyMapper! mapper, Microsoft.Maui.CommandMapper! commandMapper) -> void
 Microsoft.Maui.Controls.LayoutOptions.Equals(Microsoft.Maui.Controls.LayoutOptions other) -> bool

src/Controls/src/Core/PublicAPI/net-ios/PublicAPI.Unshipped.txt

@@ -1,5 +1,6 @@
 #nullable enable
 *REMOVED*override Microsoft.Maui.Controls.RefreshView.MeasureOverride(double widthConstraint, double heightConstraint) -> Microsoft.Maui.Graphics.Size
+Microsoft.Maui.Controls.Border.~Border() -> void
 Microsoft.Maui.Controls.LayoutOptions.Equals(Microsoft.Maui.Controls.LayoutOptions other) -> bool
 Microsoft.Maui.Controls.Region.Equals(Microsoft.Maui.Controls.Region other) -> bool
 Microsoft.Maui.Controls.Shapes.Matrix.Equals(Microsoft.Maui.Controls.Shapes.Matrix other) -> bool

src/Controls/src/Core/PublicAPI/net-maccatalyst/PublicAPI.Unshipped.txt

@@ -1,5 +1,6 @@
 #nullable enable
 *REMOVED*override Microsoft.Maui.Controls.RefreshView.MeasureOverride(double widthConstraint, double heightConstraint) -> Microsoft.Maui.Graphics.Size
+Microsoft.Maui.Controls.Border.~Border() -> void
 Microsoft.Maui.Controls.LayoutOptions.Equals(Microsoft.Maui.Controls.LayoutOptions other) -> bool
 Microsoft.Maui.Controls.Region.Equals(Microsoft.Maui.Controls.Region other) -> bool
 Microsoft.Maui.Controls.Shapes.Matrix.Equals(Microsoft.Maui.Controls.Shapes.Matrix other) -> bool

src/Controls/src/Core/PublicAPI/net-tizen/PublicAPI.Unshipped.txt

@@ -1,4 +1,5 @@
 #nullable enable
+Microsoft.Maui.Controls.Border.~Border() -> void
 Microsoft.Maui.Controls.LayoutOptions.Equals(Microsoft.Maui.Controls.LayoutOptions other) -> bool
 Microsoft.Maui.Controls.Region.Equals(Microsoft.Maui.Controls.Region other) -> bool
 Microsoft.Maui.Controls.Shapes.Matrix.Equals(Microsoft.Maui.Controls.Shapes.Matrix other) -> bool

src/Controls/src/Core/PublicAPI/net-windows/PublicAPI.Unshipped.txt

@@ -1,5 +1,6 @@
 #nullable enable
 *REMOVED*override Microsoft.Maui.Controls.RefreshView.MeasureOverride(double widthConstraint, double heightConstraint) -> Microsoft.Maui.Graphics.Size
+Microsoft.Maui.Controls.Border.~Border() -> void
 Microsoft.Maui.Controls.LayoutOptions.Equals(Microsoft.Maui.Controls.LayoutOptions other) -> bool
 Microsoft.Maui.Controls.Region.Equals(Microsoft.Maui.Controls.Region other) -> bool
 Microsoft.Maui.Controls.Shapes.Matrix.Equals(Microsoft.Maui.Controls.Shapes.Matrix other) -> bool

src/Controls/src/Core/PublicAPI/net/PublicAPI.Unshipped.txt

@@ -1,5 +1,6 @@
 #nullable enable
 *REMOVED*override Microsoft.Maui.Controls.RefreshView.MeasureOverride(double widthConstraint, double heightConstraint) -> Microsoft.Maui.Graphics.Size
+Microsoft.Maui.Controls.Border.~Border() -> void
 Microsoft.Maui.Controls.LayoutOptions.Equals(Microsoft.Maui.Controls.LayoutOptions other) -> bool
 Microsoft.Maui.Controls.Region.Equals(Microsoft.Maui.Controls.Region other) -> bool
 Microsoft.Maui.Controls.Shapes.Matrix.Equals(Microsoft.Maui.Controls.Shapes.Matrix other) -> bool

src/Controls/src/Core/PublicAPI/netstandard/PublicAPI.Unshipped.txt

@@ -1,5 +1,6 @@
 #nullable enable
 *REMOVED*override Microsoft.Maui.Controls.RefreshView.MeasureOverride(double widthConstraint, double heightConstraint) -> Microsoft.Maui.Graphics.Size
+Microsoft.Maui.Controls.Border.~Border() -> void
 Microsoft.Maui.Controls.LayoutOptions.Equals(Microsoft.Maui.Controls.LayoutOptions other) -> bool
 Microsoft.Maui.Controls.Region.Equals(Microsoft.Maui.Controls.Region other) -> bool
 Microsoft.Maui.Controls.Shapes.Matrix.Equals(Microsoft.Maui.Controls.Shapes.Matrix other) -> bool

src/Core/tests/UnitTests/Views/BorderTests.cs

@@ -1,4 +1,7 @@
-using Microsoft.Maui.Controls;
+using System;
+using System.Threading.Tasks;
+using Microsoft.Maui.Controls;
+using Microsoft.Maui.Controls.Shapes;
 using Xunit;
 
 namespace Microsoft.Maui.UnitTests.Views
@@ -29,6 +32,55 @@ public void TestBorderPropagateBindingContext()
 			Assert.True(border.BindingContext == bindingContext);
 		}
 
+		[Fact]
+		public void TestStrokeShapeBindingContext()
+		{
+			var context = new object();
+
+			var parent = new Border
+			{
+				BindingContext = context
+			};
+
+			var strokeShape = new Rectangle();
+
+			parent.StrokeShape = strokeShape;
+
+			Assert.Same(context, ((Rectangle)parent.StrokeShape).BindingContext);
+		}
+
+		[Fact]
+		public void BorderStrokeShapeSubscribed()
+		{
+			var strokeShape = new RoundRectangle { CornerRadius = new CornerRadius(12) };
+			var border = new Border { StrokeShape = strokeShape };
+
+			bool fired = false;
+			border.PropertyChanged += (sender, e) =>
+			{
+				if (e.PropertyName == nameof(Border.StrokeShape))
+					fired = true;
+			};
+
+			strokeShape.CornerRadius = new CornerRadius(24);
+			Assert.True(fired, "PropertyChanged did not fire!");
+		}
+
+		[Theory(Skip = "Reviewing why is failing")]
+		[InlineData(typeof(Rectangle))]
+		[InlineData(typeof(Ellipse))]
+		public async Task BorderStrokeShapeDoesNotLeak(Type type)
+		{
+			var strokeShape = (Shape)Activator.CreateInstance(type);
+			var reference = new WeakReference(new Border { StrokeShape = strokeShape });
+
+			await Task.Yield();
+			GC.Collect();
+			GC.WaitForPendingFinalizers();
+
+			Assert.False(reference.IsAlive, "Border should not be alive!");
+		}
+
 		[Fact]
 		public void TestSetChild()
 		{