Make VisualParent a direct PerspexProperty.

src/Perspex.SceneGraph/Visual.cs

@@ -64,6 +64,12 @@ namespace Perspex
         public static readonly PerspexProperty<RelativePoint> TransformOriginProperty =
             PerspexProperty.Register<Visual, RelativePoint>(nameof(TransformOrigin), defaultValue: RelativePoint.Center);
 
+        /// <summary>
+        /// Defines the <see cref="IVisual.VisualParent"/> property.
+        /// </summary>
+        public static readonly PerspexProperty<IVisual> VisualParentProperty =
+            PerspexProperty.RegisterDirect<Visual, IVisual>("VisualParent", o => o._visualParent);
+
         /// <summary>
         /// Defines the <see cref="ZIndex"/> property.
         /// </summary>
@@ -83,7 +89,7 @@ namespace Perspex
         /// <summary>
         /// Holds the parent of the visual.
         /// </summary>
-        private Visual _visualParent;
+        private IVisual _visualParent;
 
         /// <summary>
         /// Whether the element is attached to the visual tree.
@@ -444,6 +450,8 @@ namespace Perspex
                 {
                     NotifyAttachedToVisualTree(newRoot);
                 }
+
+                RaisePropertyChanged(VisualParentProperty, old, value, BindingPriority.LocalValue);
             }
         }
 

tests/Perspex.SceneGraph.UnitTests/VisualTests.cs

@@ -1,6 +1,8 @@
 // Copyright (c) The Perspex Project. All rights reserved.
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
+using System;
+using System.Collections.Generic;
 using System.Linq;
 using Perspex.VisualTree;
 using Xunit;
@@ -31,6 +33,20 @@ namespace Perspex.SceneGraph.UnitTests
             Assert.Equal(target, child.InheritanceParent);
         }
 
+        [Fact]
+        public void Added_Child_Should_Notify_VisualParent_Changed()
+        {
+            var target = new TestVisual();
+            var child = new TestVisual();
+            var parents = new List<IVisual>();
+
+            child.GetObservable(Visual.VisualParentProperty).Subscribe(x => parents.Add(x));
+            target.AddChild(child);
+            target.RemoveChild(child);
+
+            Assert.Equal(new IVisual[] { null, target, null }, parents);
+        }
+
         [Fact]
         public void Removed_Child_Should_Have_VisualParent_Cleared()
         {