Add FocusSelectedItemBehavior

src/Avalonia.Xaml.Interactions.Custom/FocusSelectedItemBehavior.cs

@@ -0,0 +1,43 @@
+using System;
+using System.Reactive.Disposables;
+using Avalonia.Controls;
+using Avalonia.Controls.Primitives;
+using Avalonia.Threading;
+
+namespace Avalonia.Xaml.Interactions.Custom;
+
+/// <summary>
+/// 
+/// </summary>
+public class FocusSelectedItemBehavior : AttachedToVisualTreeBehavior<ItemsControl>
+{
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <param name="disposable"></param>
+    protected override void OnAttachedToVisualTree(CompositeDisposable disposable)
+    {
+        var dispose = AssociatedObject?
+            .GetObservable(SelectingItemsControl.SelectedItemProperty)
+            .Subscribe(selectedItem =>
+            {
+                var item = selectedItem;
+                if (item is not null)
+                {
+                    Dispatcher.UIThread.Post(() =>
+                    {
+                        var container = AssociatedObject.ContainerFromItem(item);
+                        if (container is not null)
+                        {
+                            container.Focus();
+                        }
+                    });
+                }
+            });
+
+        if (dispose is not null)
+        {
+            disposable.Add(dispose);
+        }
+    }
+}