Update sample for macOS checked menu item

samples/ControlCatalog/MainWindow.xaml

@@ -36,6 +36,15 @@
           </NativeMenu>
         </NativeMenuItem.Menu>
       </NativeMenuItem>
+      <NativeMenuItem Header="Options">
+        <NativeMenuItem.Menu>
+          <NativeMenu>
+            <NativeMenuItem Header="Check Me Out" 
+                            Command="{Binding ToggleMenuItemCheckedCommand}"
+                            IsChecked="{Binding IsMenuItemChecked}"  />
+          </NativeMenu>
+        </NativeMenuItem.Menu>
+      </NativeMenuItem>
     </NativeMenu>
   </NativeMenu.Menu>
 

samples/ControlCatalog/ViewModels/MainWindowViewModel.cs

@@ -10,6 +10,8 @@ namespace ControlCatalog.ViewModels
     {
         private IManagedNotificationManager _notificationManager;
 
+        private bool _isMenuItemChecked = true;
+
         public MainWindowViewModel(IManagedNotificationManager notificationManager)
         {
             _notificationManager = notificationManager;
@@ -42,6 +44,11 @@ namespace ControlCatalog.ViewModels
             {
                 (App.Current.ApplicationLifetime as IClassicDesktopStyleApplicationLifetime).Shutdown();
             });
+
+            ToggleMenuItemCheckedCommand = ReactiveCommand.Create(() => 
+            {
+                IsMenuItemChecked = !IsMenuItemChecked;
+            });
         }
 
         public IManagedNotificationManager NotificationManager
@@ -50,6 +57,12 @@ namespace ControlCatalog.ViewModels
             set { this.RaiseAndSetIfChanged(ref _notificationManager, value); }
         }
 
+        public bool IsMenuItemChecked
+        {
+            get { return _isMenuItemChecked; }
+            set { this.RaiseAndSetIfChanged(ref _isMenuItemChecked, value); }
+        }
+
         public ReactiveCommand<Unit, Unit> ShowCustomManagedNotificationCommand { get; }
 
         public ReactiveCommand<Unit, Unit> ShowManagedNotificationCommand { get; }
@@ -59,5 +72,7 @@ namespace ControlCatalog.ViewModels
         public ReactiveCommand<Unit, Unit> AboutCommand { get; }
 
         public ReactiveCommand<Unit, Unit> ExitCommand { get; }
+
+        public ReactiveCommand<Unit, Unit> ToggleMenuItemCheckedCommand { get; }
     }
 }