fix direct property implementations on nativemenu item.

src/Avalonia.Controls/NativeMenu.cs

@@ -3,8 +3,6 @@ using System.Collections;
 using System.Collections.Generic;
 using System.Collections.Specialized;
 using Avalonia.Collections;
-using Avalonia.Data;
-using Avalonia.LogicalTree;
 using Avalonia.Metadata;
 
 namespace Avalonia.Controls

src/Avalonia.Controls/NativeMenuItem.cs

@@ -10,6 +10,7 @@ namespace Avalonia.Controls
         private string _header;
         private KeyGesture _gesture;
         private bool _enabled = true;
+        private ICommand _command;
 
         private NativeMenu _menu;
 
@@ -55,13 +56,7 @@ namespace Avalonia.Controls
         }
 
         public static readonly DirectProperty<NativeMenuItem, NativeMenu> MenuProperty =
-            AvaloniaProperty.RegisterDirect<NativeMenuItem, NativeMenu>(nameof(Menu), o => o._menu,
-                (o, v) =>
-                {
-                    if (v.Parent != null && v.Parent != o)
-                        throw new InvalidOperationException("NativeMenu already has a parent");
-                    o._menu = v;
-                });
+            AvaloniaProperty.RegisterDirect<NativeMenuItem, NativeMenu>(nameof(Menu), o => o.Menu, (o, v) => o.Menu = v);
 
         public NativeMenu Menu
         {
@@ -75,38 +70,26 @@ namespace Avalonia.Controls
         }
 
         public static readonly DirectProperty<NativeMenuItem, string> HeaderProperty =
-            AvaloniaProperty.RegisterDirect<NativeMenuItem, string>(nameof(Header), o => o._header, (o, v) => o._header = v);
+            AvaloniaProperty.RegisterDirect<NativeMenuItem, string>(nameof(Header), o => o.Header, (o, v) => o.Header = v);
 
         public string Header
         {
-            get => GetValue(HeaderProperty);
-            set => SetValue(HeaderProperty, value);
+            get => _header;
+            set => SetAndRaise(HeaderProperty, ref _header, value);
         }
 
         public static readonly DirectProperty<NativeMenuItem, KeyGesture> GestureProperty =
-            AvaloniaProperty.RegisterDirect<NativeMenuItem, KeyGesture>(nameof(Gesture), o => o._gesture, (o, v) => o._gesture = v);
+            AvaloniaProperty.RegisterDirect<NativeMenuItem, KeyGesture>(nameof(Gesture), o => o.Gesture, (o, v) => o.Gesture = v);
 
         public KeyGesture Gesture
         {
-            get => GetValue(GestureProperty);
-            set => SetValue(GestureProperty, value);
-        }
-
-        private ICommand _command;
+            get => _gesture;
+            set => SetAndRaise(GestureProperty, ref _gesture, value);
+        }        
 
         public static readonly DirectProperty<NativeMenuItem, ICommand> CommandProperty =
            AvaloniaProperty.RegisterDirect<NativeMenuItem, ICommand>(nameof(Command),
-               o => o._command, (o, v) =>
-               {
-                   if (o._command != null)
-                       WeakSubscriptionManager.Unsubscribe(o._command,
-                           nameof(ICommand.CanExecuteChanged), o._canExecuteChangedSubscriber);
-                   o._command = v;
-                   if (o._command != null)
-                       WeakSubscriptionManager.Subscribe(o._command,
-                           nameof(ICommand.CanExecuteChanged), o._canExecuteChangedSubscriber);
-                   o.CanExecuteChanged();
-               });
+               o => o.Command, (o, v) => o.Command = v);
 
         /// <summary>
         /// Defines the <see cref="CommandParameter"/> property.
@@ -115,13 +98,12 @@ namespace Avalonia.Controls
             Button.CommandParameterProperty.AddOwner<MenuItem>();
 
         public static readonly DirectProperty<NativeMenuItem, bool> EnabledProperty =
-           AvaloniaProperty.RegisterDirect<NativeMenuItem, bool>(nameof(Enabled), o => o._enabled,
-               (o, v) => o._enabled = v, true);
+           AvaloniaProperty.RegisterDirect<NativeMenuItem, bool>(nameof(Enabled), o => o.Enabled, (o, v) => o.Enabled = v, true);
 
         public bool Enabled
         {
-            get => GetValue(EnabledProperty);
-            set => SetValue(EnabledProperty, value);
+            get => _enabled;
+            set => SetAndRaise(EnabledProperty, ref _enabled, value);
         }
 
         void CanExecuteChanged()
@@ -133,8 +115,21 @@ namespace Avalonia.Controls
 
         public ICommand Command
         {
-            get => GetValue(CommandProperty);
-            set => SetValue(CommandProperty, value);
+            get => _command;
+            set
+            {
+                if (_command != null)
+                    WeakSubscriptionManager.Unsubscribe(_command,
+                        nameof(ICommand.CanExecuteChanged), _canExecuteChangedSubscriber);
+
+                SetAndRaise(CommandProperty, ref _command, value);
+                
+                if (_command != null)
+                    WeakSubscriptionManager.Subscribe(_command,
+                        nameof(ICommand.CanExecuteChanged), _canExecuteChangedSubscriber);
+                
+                CanExecuteChanged();                
+            }
         }
 
         /// <summary>