Fix TabItem memory leak (#12418)

* TabItem: dispose _ownerSubscriptions when item is detached from visual tree

* TabItem: update of TabStripPlacement moved to TabControl

* TabControl: iterate over ItemsPresenterPart's children instead of calling ContainerFromIndex

* TabItem: SubscribeToOwnerProperties marked as obsolete

---------

Co-authored-by: Dmitry Zhelnin <d.zhelnin@of-group.ru>

src/Avalonia.Controls/TabControl.cs

@@ -73,6 +73,7 @@ namespace Avalonia.Controls
         {
             SelectionModeProperty.OverrideDefaultValue<TabControl>(SelectionMode.AlwaysSelected);
             ItemsPanelProperty.OverrideDefaultValue<TabControl>(DefaultPanel);
+            TabStripPlacementProperty.Changed.AddClassHandler<TabControl>((x, e) => x.UpdateTabStripPlacement());
             AffectsMeasure<TabControl>(TabStripPlacementProperty);
             SelectedItemProperty.Changed.AddClassHandler<TabControl>((x, e) => x.UpdateSelectedContent());
             AutomationProperties.ControlTypeOverrideProperty.OverrideDefaultValue<TabControl>(AutomationControlType.Tab);
@@ -153,7 +154,7 @@ namespace Avalonia.Controls
 
         protected internal override Control CreateContainerForItemOverride(object? item, int index, object? recycleKey)
         {
-            return new TabItem();
+            return new TabItem { TabStripPlacement = TabStripPlacement };
         }
 
         protected internal override bool NeedsContainerOverride(object? item, int index, out object? recycleKey)
@@ -229,6 +230,8 @@ namespace Avalonia.Controls
             ItemsPresenterPart = e.NameScope.Find<ItemsPresenter>("PART_ItemsPresenter");
             ItemsPresenterPart?.ApplyTemplate();
 
+            UpdateTabStripPlacement();
+
             // Set TabNavigation to Once on the panel if not already set and
             // forward the TabOnceActiveElement to the panel.
             if (ItemsPresenterPart?.Panel is { } panel)
@@ -306,5 +309,22 @@ namespace Avalonia.Controls
                     change.GetNewValue<IInputElement?>());
             }
         }
+
+        private void UpdateTabStripPlacement()
+        {
+            var controls = ItemsPresenterPart?.Panel?.Children;
+            if (controls is null)
+            {
+                return;
+            }
+
+            foreach (var control in controls)
+            {
+                if (control is TabItem tabItem)
+                {
+                    tabItem.TabStripPlacement = TabStripPlacement;
+                }
+            }
+        }
     }
 }

src/Avalonia.Controls/TabItem.cs

@@ -4,8 +4,6 @@ using Avalonia.Automation.Peers;
 using Avalonia.Controls.Metadata;
 using Avalonia.Controls.Mixins;
 using Avalonia.Controls.Primitives;
-using Avalonia.Reactive;
-using Avalonia.VisualTree;
 
 namespace Avalonia.Controls
 {
@@ -16,7 +14,6 @@ namespace Avalonia.Controls
     public class TabItem : HeaderedContentControl, ISelectable
     {
         private Dock? _tabStripPlacement;
-        private IDisposable? _ownerSubscriptions;
 
         /// <summary>
         /// Defines the <see cref="TabStripPlacement"/> property.
@@ -48,7 +45,7 @@ namespace Avalonia.Controls
         public Dock? TabStripPlacement
         {
             get => _tabStripPlacement;
-            private set => SetAndRaise(TabStripPlacementProperty, ref _tabStripPlacement, value);
+            internal set => SetAndRaise(TabStripPlacementProperty, ref _tabStripPlacement, value);
         }
 
         /// <summary>
@@ -62,22 +59,9 @@ namespace Avalonia.Controls
 
         protected override AutomationPeer OnCreateAutomationPeer() => new ListItemAutomationPeer(this);
 
-        protected override void OnAttachedToVisualTree(VisualTreeAttachmentEventArgs e)
+        [Obsolete("Owner manages its children properties by itself")]
-        {
-            base.OnAttachedToVisualTree(e);
-
-            _ownerSubscriptions?.Dispose();
-            _ownerSubscriptions = null;
-
-            if (this.FindAncestorOfType<TabControl>() is { } owner && owner.IndexFromContainer(this) != -1)
-            {
-                SubscribeToOwnerProperties(owner);
-            }
-        }
-
         protected void SubscribeToOwnerProperties(AvaloniaObject owner)
         {
-            _ownerSubscriptions = owner.GetObservable(TabControl.TabStripPlacementProperty).Subscribe(v => TabStripPlacement = v);
         }
 
         private void UpdateHeader(AvaloniaPropertyChangedEventArgs obj)