MenuFlyout.Items -> ItemsSource.

src/Avalonia.Controls/Flyouts/MenuFlyout.cs

@@ -1,6 +1,5 @@
 using System.Collections;
 using System.ComponentModel;
-using Avalonia.Collections;
 using Avalonia.Controls.Primitives;
 using Avalonia.Controls.Templates;
 using Avalonia.Metadata;
@@ -12,17 +11,15 @@ namespace Avalonia.Controls
     {
         public MenuFlyout()
         {
-            _items = new AvaloniaList<object>();
+            Items = new ItemCollection();
         }
 
         /// <summary>
-        /// Defines the <see cref="Items"/> property
+        /// Defines the <see cref="ItemsSource"/> property
         /// </summary>
-        public static readonly DirectProperty<MenuFlyout, IEnumerable?> ItemsProperty =
-            AvaloniaProperty.RegisterDirect<MenuFlyout, IEnumerable?>(
-                nameof(Items),
-                x => x.Items,
-                (x, v) => x.Items = v);
+        public static readonly StyledProperty<IEnumerable?> ItemsSourceProperty =
+            AvaloniaProperty.Register<MenuFlyout, IEnumerable?>(
+                nameof(ItemsSource));
 
         /// <summary>
         /// Defines the <see cref="ItemTemplate"/> property
@@ -45,14 +42,16 @@ namespace Avalonia.Controls
         
         public Classes FlyoutPresenterClasses => _classes ??= new Classes();
 
+        [Content]
+        public ItemCollection Items { get; }
+
         /// <summary>
         /// Gets or sets the items of the MenuFlyout
         /// </summary>
-        [Content]
-        public IEnumerable? Items
+        public IEnumerable? ItemsSource
         {
-            get => _items;
-            set => SetAndRaise(ItemsProperty, ref _items, value);
+            get => GetValue(ItemsSourceProperty);
+            set => SetValue(ItemsSourceProperty, value);
         }
 
         /// <summary>
@@ -83,14 +82,13 @@ namespace Avalonia.Controls
         }
         
         private Classes? _classes;
-        private IEnumerable? _items;
         private IDataTemplate? _itemTemplate;
 
         protected override Control CreatePresenter()
         {
             return new MenuFlyoutPresenter
             {
-                [!ItemsControl.ItemsSourceProperty] = this[!ItemsProperty],
+                ItemsSource = Items,
                 [!ItemsControl.ItemTemplateProperty] = this[!ItemTemplateProperty],
                 [!ItemsControl.ItemContainerThemeProperty] = this[!ItemContainerThemeProperty],
             };
@@ -113,5 +111,13 @@ namespace Avalonia.Controls
 
             base.OnOpening(args);
         }
+
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
+        {
+            base.OnPropertyChanged(change);
+
+            if (change.Property == ItemsSourceProperty)
+                Items.SetItemsSource(change.GetNewValue<IEnumerable?>());
+        }
     }
 }

src/Avalonia.Controls/ItemsSourceView.cs

@@ -262,7 +262,7 @@ namespace Avalonia.Controls
 
             _source = source switch
             {
-                ItemsSourceView => throw new ArgumentException("Cannot wrap an existing ItemsSourceView.", nameof(source)),
+                ItemsSourceView isv => isv.Source,
                 IList list => list,
                 INotifyCollectionChanged => throw new ArgumentException(
                     "Collection implements INotifyCollectionChanged but not IList.",

tests/Avalonia.Controls.UnitTests/MaskedTextBoxTests.cs

@@ -72,7 +72,7 @@ namespace Avalonia.Controls.UnitTests
                     Text = "1234",
                     ContextFlyout = new MenuFlyout
                     {
-                        Items = new List<MenuItem>
+                        Items =
                         {
                             new MenuItem { Header = "Item 1" },
                             new MenuItem {Header = "Item 2" },

tests/Avalonia.Controls.UnitTests/MenuItemTests.cs

@@ -230,7 +230,7 @@ namespace Avalonia.Controls.UnitTests
                     return true;
                 });
                 var target = new MenuItem();
-                var flyout = new MenuFlyout { Items = new AvaloniaList<MenuItem> { target } };
+                var flyout = new MenuFlyout { Items = { target } };
                 var button = new Button { Flyout = flyout };
                 var window = new Window { Content = button };
                 window.ApplyStyling();

tests/Avalonia.Controls.UnitTests/TextBoxTests.cs

@@ -93,7 +93,7 @@ namespace Avalonia.Controls.UnitTests
                     Text = "1234",
                     ContextFlyout = new MenuFlyout
                     {
-                        Items = new List<MenuItem>
+                        Items =
                         {
                             new MenuItem { Header = "Item 1" },
                             new MenuItem {Header = "Item 2" },