fix(controls): fix radio MenuItem grouping in MenuFlyout

samples/ControlCatalog/Pages/ContextFlyoutPage.xaml

@@ -54,6 +54,15 @@
                           IsHitTestVisible="False" />
               </MenuItem.Icon>
             </MenuItem>
+            <MenuItem GroupName="Radio-ableMenuItem"
+                      Header="Menu Item with _RadioButton1"
+                      IsChecked="True"
+                      StaysOpenOnClick="True"
+                      ToggleType="Radio" />
+            <MenuItem GroupName="Radio-ableMenuItem"
+                      Header="Menu Item with _RadioButton2"
+                      StaysOpenOnClick="True"
+                      ToggleType="Radio" />
           </MenuFlyout>
         </Border.ContextFlyout>
         <TextBlock Text="Defined in XAML" />

samples/ControlCatalog/Pages/ContextMenuPage.xaml

@@ -43,6 +43,15 @@
                           IsHitTestVisible="False" />
               </MenuItem.Icon>
             </MenuItem>
+            <MenuItem GroupName="Radio-ableMenuItem"
+                      Header="Menu Item with _RadioButton1"
+                      IsChecked="True"
+                      StaysOpenOnClick="True"
+                      ToggleType="Radio" />
+            <MenuItem GroupName="Radio-ableMenuItem"
+                      Header="Menu Item with _RadioButton2"
+                      StaysOpenOnClick="True"
+                      ToggleType="Radio" />
             <MenuItem Header="Menu Item that won't close on click" StaysOpenOnClick="True" />
           </ContextMenu>
         </Border.ContextMenu>

src/Avalonia.Controls/MenuItem.cs

@@ -14,6 +14,7 @@
 using Avalonia.Interactivity;
 using Avalonia.LogicalTree;
 using Avalonia.Reactive;
+using Avalonia.VisualTree;
 
 namespace Avalonia.Controls
 {
@@ -387,7 +388,9 @@ public string? GroupName
         /// <inheritdoc/>
         IEnumerable<IMenuItem> IMenuElement.SubItems => LogicalChildren.OfType<IMenuItem>();
 
-        private IMenuInteractionHandler? MenuInteractionHandler => this.FindLogicalAncestorOfType<MenuBase>()?.InteractionHandler;
+        private IMenuInteractionHandler? MenuInteractionHandler =>
+            this.FindLogicalAncestorOfType<MenuBase>()?.InteractionHandler ??
+            this.FindAncestorOfType<MenuBase>()?.InteractionHandler;
 
         /// <summary>
         /// Opens the submenu.
@@ -470,6 +473,7 @@ protected override void OnAttachedToVisualTree(VisualTreeAttachmentEventArgs e)
             base.OnAttachedToVisualTree(e);
 
             TryUpdateCanExecute();
+            RegisterInMenuInteractionHandler();
         }
 
         protected override void OnDetachedFromLogicalTree(LogicalTreeAttachmentEventArgs e)
@@ -908,6 +912,16 @@ private void PopupClosed(object? sender, EventArgs e)
             SelectedItem = null;
         }
 
+        private void RegisterInMenuInteractionHandler()
+        {
+            if (ToggleType != MenuItemToggleType.Radio || MenuInteractionHandler is not DefaultMenuInteractionHandler handler)
+            {
+                return;
+            }
+
+            handler.OnGroupOrTypeChanged(this, null);
+        }
+
         void ICommandSource.CanExecuteChanged(object sender, EventArgs e) => CanExecuteChangedHandler(sender, e);
 
         void IClickableControl.RaiseClick()

src/Avalonia.Controls/RadioButtonGroupManager.cs

@@ -41,6 +41,23 @@ public void Add(IRadioButton radioButton)
                 _registeredGroups.Add(groupName, group);
             }
 
+            int i = 0;
+            while (i < group.Count)
+            {
+                if (!group[i].TryGetTarget(out var current))
+                {
+                    group.RemoveAt(i);
+                    continue;
+                }
+
+                if (current == radioButton)
+                {
+                    return;
+                }
+
+                i++;
+            }
+
             group.Add(new WeakReference<IRadioButton>(radioButton));
         }
     }

tests/Avalonia.Controls.UnitTests/MenuItemTests.cs

@@ -560,6 +560,47 @@ public void Radio_MenuItem_In_Same_Group_Is_Unchecked()
             Assert.True(menuItem3.IsChecked);
         }
 
+        [Fact]
+        public void Radio_MenuItem_In_Same_Group_In_MenuFlyout_Is_Unchecked()
+        {
+            using var app = Application();
+
+            var menuItem1 = new MenuItem
+            {
+                GroupName = "A",
+                IsChecked = true,
+                StaysOpenOnClick = true,
+                ToggleType = MenuItemToggleType.Radio,
+            };
+            var menuItem2 = new MenuItem
+            {
+                GroupName = "A",
+                IsChecked = false,
+                StaysOpenOnClick = true,
+                ToggleType = MenuItemToggleType.Radio,
+            };
+
+            var flyout = new MenuFlyout
+            {
+                Items =
+                {
+                    menuItem1,
+                    menuItem2,
+                }
+            };
+            var button = new Button { ContextFlyout = flyout };
+            var window = new Window { Content = button };
+
+            window.Show();
+            flyout.ShowAt(button);
+            Dispatcher.UIThread.RunJobs(DispatcherPriority.Loaded, TestContext.Current.CancellationToken);
+
+            menuItem2.IsChecked = true;
+
+            Assert.False(menuItem1.IsChecked);
+            Assert.True(menuItem2.IsChecked);
+        }
+
         [Fact]
         public void Radio_Menu_Group_Can_Be_Changed_In_Runtime()
         {