first stage implementation of deinitialisation of menu items.

src/Avalonia.Native/IAvnAppMenu.cs

@@ -23,6 +23,8 @@ namespace Avalonia.Native.Interop
             item.Update(null, null, null);
             RemoveItem(item);
 
+            item.Deinitialise();
+
             item.Dispose();
         }
 
@@ -35,12 +37,18 @@ namespace Avalonia.Native.Interop
             InsertItem(index, item);
         }
 
-        private void InsertNewAt(int index, IAvnAppMenuItem item)
+        private IAvnAppMenuItem CreateNewAt(IAvaloniaNativeFactory factory, int index, NativeMenuItemBase item)
         {
-            _menuItemLookup.Add(item.ManagedMenuItem, item);
-            _menuItems.Insert(index, item);
+            var result = CreateNew(factory, item);
 
-            InsertItem(index, item);
+            result.Initialise();
+
+            _menuItemLookup.Add(result.ManagedMenuItem, result);
+            _menuItems.Insert(index, result);
+
+            InsertItem(index, result);
+
+            return result;
         }
 
         private IAvnAppMenuItem CreateNew(IAvaloniaNativeFactory factory, NativeMenuItemBase item)
@@ -84,9 +92,7 @@ namespace Avalonia.Native.Interop
 
                 if (i >= _menuItems.Count)
                 {
-                    nativeItem = CreateNew(factory, menu.Items[i]);
-
-                    InsertNewAt(i, nativeItem);
+                    nativeItem = CreateNewAt(factory, i, menu.Items[i]);
                 }
                 else if (menu.Items[i] == _menuItems[i].ManagedMenuItem)
                 {
@@ -98,9 +104,7 @@ namespace Avalonia.Native.Interop
                 }
                 else
                 {
-                    nativeItem = CreateNew(factory, menu.Items[i]);
-
-                    InsertNewAt(i, nativeItem);
+                    nativeItem = CreateNewAt(factory, i, menu.Items[i]);
                 }
 
                 if (menu.Items[i] is NativeMenuItem nmi)

src/Avalonia.Native/IAvnAppMenuItem.cs

@@ -10,7 +10,7 @@ namespace Avalonia.Native.Interop
         private IAvnAppMenu _subMenu;
         private AvaloniaNativeMenuExporter _exporter;
         private CompositeDisposable _propertyDisposables = new CompositeDisposable();
-        private PredicateCallback _currentAction;
+        private IDisposable _currentActionDisposable;
 
         public NativeMenuItemBase ManagedMenuItem { get; set; }
 
@@ -33,9 +33,9 @@ namespace Avalonia.Native.Interop
 
         private void UpdateAction (NativeMenuItem item)
         {
-            _currentAction?.Dispose();
+            _currentActionDisposable?.Dispose();
 
-            SetAction(new PredicateCallback(() =>
+            var action = new PredicateCallback(() =>
             {
                 if (item.Command != null || item.HasClickHandlers)
                 {
@@ -43,7 +43,41 @@ namespace Avalonia.Native.Interop
                 }
 
                 return false;
-            }), new MenuActionCallback(() => { item.RaiseClick(); }));
+            });
+
+            var callback = new MenuActionCallback(() => { item.RaiseClick(); });
+
+            _currentActionDisposable = Disposable.Create(() =>
+            {
+                action.Dispose();
+                callback.Dispose();
+            });
+
+            SetAction(action, callback);
+        }
+
+        internal void Initialise()
+        {
+            _propertyDisposables.Add(Disposable.Create(() => ManagedMenuItem.GetObservable(NativeMenuItem.HeaderProperty)
+                .Subscribe(x => UpdateTitle(x))));
+
+            _propertyDisposables.Add(Disposable.Create(() => ManagedMenuItem.GetObservable(NativeMenuItem.GestureProperty)
+                .Subscribe(x => UpdateGesture(x))));
+
+            _propertyDisposables.Add(Disposable.Create(() => ManagedMenuItem.GetObservable(NativeMenuItem.CommandProperty)
+                .Subscribe(x => UpdateAction(ManagedMenuItem as NativeMenuItem))));
+        }
+
+        internal void Deinitialise ()
+        {
+            if(_subMenu != null)
+            {
+                _subMenu.Update(null, null, null);
+                _subMenu = null;
+            }
+
+            _propertyDisposables?.Dispose();
+            _currentActionDisposable?.Dispose();
         }
 
         internal IDisposable Update(AvaloniaNativeMenuExporter exporter, IAvaloniaNativeFactory factory, NativeMenuItem item)
@@ -54,19 +88,10 @@ namespace Avalonia.Native.Interop
 
             ManagedMenuItem = item;
 
-            _propertyDisposables.Add(Disposable.Create(() => ManagedMenuItem.GetObservable(NativeMenuItem.HeaderProperty)
-                .Subscribe(x => UpdateTitle(x))));
-
             UpdateTitle(item.Header);
 
-            _propertyDisposables.Add(Disposable.Create(() => ManagedMenuItem.GetObservable(NativeMenuItem.GestureProperty)
-                .Subscribe(x => UpdateGesture(x))));
-
             UpdateGesture(item.Gesture);
 
-            _propertyDisposables.Add(Disposable.Create(() => ManagedMenuItem.GetObservable(NativeMenuItem.CommandProperty)
-                .Subscribe(x => UpdateAction(ManagedMenuItem as NativeMenuItem))));
-
             UpdateAction(ManagedMenuItem as NativeMenuItem);
 
             if (item.Menu != null)