Remove BypassLogicalChildrenManagement and use OnPropertyChanged

src/Avalonia.Controls/ContentControl.cs

@@ -40,11 +40,6 @@ namespace Avalonia.Controls
         public static readonly StyledProperty<VerticalAlignment> VerticalContentAlignmentProperty =
             AvaloniaProperty.Register<ContentControl, VerticalAlignment>(nameof(VerticalContentAlignment));
 
-        static ContentControl()
-        {
-            ContentProperty.Changed.AddClassHandler<ContentControl>((x, e) => x.ContentChanged(e));
-        }
-
         /// <summary>
         /// Gets or sets the content to display.
         /// </summary>
@@ -95,22 +90,20 @@ namespace Avalonia.Controls
         /// <inheritdoc/>
         IAvaloniaList<ILogical> IContentPresenterHost.LogicalChildren => LogicalChildren;
 
-        /// <summary>
-        /// Determine whether <see cref="ContentControl"/> manage his LogicalChildren 
-        ///(default behavior) himself, or leaves the management to the inherited control.
-        /// </summary>
-        /// <remarks>
-		/// The default value is false, So the <see cref="ContentControl"/> manages itself, 
-        /// if you want to bypass this behavior and manage LogicalChildren yourself, set 
-        /// the <see cref="BypassLogicalChildrenManagement"/> to true.
-		/// </remarks>
-        protected virtual bool BypassLogicalChildrenManagement => false;
-
         /// <inheritdoc/>
         bool IContentPresenterHost.RegisterContentPresenter(ContentPresenter presenter)
         {
             return RegisterContentPresenter(presenter);
         }
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
+        {
+            base.OnPropertyChanged(change);
+
+            if (change.Property == ContentProperty)
+            {
+                ContentChanged(change);
+            }
+        }
 
         /// <summary>
         /// Called when an <see cref="ContentPresenter"/> is registered with the control.
@@ -129,11 +122,6 @@ namespace Avalonia.Controls
 
         private void ContentChanged(AvaloniaPropertyChangedEventArgs e)
         {
-            if (BypassLogicalChildrenManagement)
-            {
-                return;
-            }
-            
             if (e.OldValue is ILogical oldChild)
             {
                 LogicalChildren.Remove(oldChild);

src/Avalonia.Controls/TransitioningContentControl.cs

@@ -36,9 +36,6 @@ public class TransitioningContentControl : ContentControl
         set => SetValue(PageTransitionProperty, value);
     }
 
-    /// <inheritdoc/>
-    protected override bool BypassLogicalChildrenManagement => true;
-
     protected override Size ArrangeOverride(Size finalSize)
     {
         var result = base.ArrangeOverride(finalSize);
@@ -101,12 +98,13 @@ public class TransitioningContentControl : ContentControl
 
     protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
     {
-        base.OnPropertyChanged(change);
-
         if (change.Property == ContentProperty)
         {
             UpdateContent(true);
+            return;
         }
+
+        base.OnPropertyChanged(change);
     }
 
     private void UpdateContent(bool withTransition)

tests/Avalonia.Controls.UnitTests/TransitioningContentControlTests.cs

@@ -184,7 +184,7 @@ namespace Avalonia.Controls.UnitTests
         }
 
         [Fact]
-        public void Logical_Children_Dont_Duplicated()
+        public void Logical_Children_Should_Not_Be_Duplicated()
         {
             using var app = Start();
             var (target, transition) = CreateTarget("");
@@ -194,18 +194,21 @@ namespace Avalonia.Controls.UnitTests
             target.Content = childControl;
 
             Assert.Equal(1, target.LogicalChildren.Count);
+            Assert.Equal(target.LogicalChildren[0], childControl);
         }
 
         [Fact]
-        public void First_Presenter_Register_TCC_As_Host()
+        public void First_Presenter_Should_Register_TCC_As_His_Host()
         {
             using var app = Start();
             var (target, transition) = CreateTarget("");
+            target.PageTransition = null;
 
             var childControl = new Control();
             target.Presenter!.Content = childControl;
 
-            Assert.Contains(childControl, target.LogicalChildren);
+            Assert.Equal(1, target.LogicalChildren.Count);
+            Assert.Equal(target.LogicalChildren[0], childControl);
         }
 
         private static IDisposable Start()