Fix windows for Mono.Mac (#1804)

- handle closing
- handle showing dialogs

src/OSX/Avalonia.MonoMac/WindowBaseImpl.cs

@@ -14,6 +14,8 @@ namespace Avalonia.MonoMac
         private readonly ManagedWindowResizeDragHelper _managedDrag;
         public CustomWindow Window { get; private set; }
 
+        private bool _closed;
+
         public WindowBaseImpl()
         {
             _managedDrag = new ManagedWindowResizeDragHelper(this, _ => { }, ResizeForManagedDrag);
@@ -78,9 +80,8 @@ namespace Avalonia.MonoMac
 
             public override void WillClose(global::MonoMac.Foundation.NSNotification notification)
             {
-                _impl.Window.Dispose();
-                _impl.Window = null;
-                _impl.Dispose();
+                _impl._closed = true;
+                _impl.Closed?.Invoke();
             }
 
             public override CGRect WillUseStandardFrame(NSWindow window, CGRect newFrame)
@@ -94,8 +95,19 @@ namespace Avalonia.MonoMac
             {
                 return true;
             }
+
+            public override void DidResize(NSNotification notification)
+            {
+                _impl.OnResized();
+            }
         }
 
+        /// <summary>
+        /// As you can't combine NSWindowDelegate overrides and events this is a workaround
+        /// </summary>
+        protected virtual void OnResized()
+        {
+        }
 
         public Point Position
         {
@@ -185,12 +197,11 @@ namespace Avalonia.MonoMac
             return cocoaScreenPoint.ConvertPointY().ToAvaloniaPoint();
         }
 
-
-
         public override void Dispose()
         {
-            Window?.Close();
-            Window?.Dispose();
+            if (!_closed)
+                Window.Close();
+            Window.Dispose();
             base.Dispose();
         }
     }

src/OSX/Avalonia.MonoMac/WindowImpl.cs

@@ -26,18 +26,19 @@ namespace Avalonia.MonoMac
             });
 
             Window.SetCanBecomeKeyAndMain();
-            
-            Window.DidResize += delegate
-            {
-                var windowState = Window.IsMiniaturized ? WindowState.Minimized
-                    : (IsZoomed ? WindowState.Maximized : WindowState.Normal);
+        }
 
-                if (windowState != _lastWindowState)
-                {
-                    _lastWindowState = windowState;
-                    WindowStateChanged?.Invoke(windowState);
-                }
-            };
+        
+        protected override void OnResized()
+        {
+            var windowState = Window.IsMiniaturized ? WindowState.Minimized
+                : (IsZoomed ? WindowState.Maximized : WindowState.Normal);
+
+            if (windowState != _lastWindowState)
+            {
+                _lastWindowState = windowState;
+                WindowStateChanged?.Invoke(windowState);
+            }
         }
 
         public WindowState WindowState
@@ -129,24 +130,47 @@ namespace Avalonia.MonoMac
         class ModalDisposable : IDisposable
         {
             readonly WindowImpl _impl;
+            readonly IntPtr _modalSession;
+            bool disposed;
 
-            public ModalDisposable(WindowImpl impl)
+            public ModalDisposable(WindowImpl impl, IntPtr modalSession)
             {
                 _impl = impl;
+                _modalSession = modalSession;
+            }
+
+            public void Continue()
+            {
+                if (disposed)
+                    return;
+
+                var response = (NSRunResponse)NSApplication.SharedApplication.RunModalSession(_modalSession);
+                if (response == NSRunResponse.Continues)
+                {
+                    Dispatcher.UIThread.Post(Continue, DispatcherPriority.ContextIdle);
+                }
+                else
+                {
+                    Logging.Logger.Log(Logging.LogEventLevel.Debug, "MonoMac", this, "Modal session ended");
+                }
             }
 
             public void Dispose()
             {
+                Logging.Logger.Log(Logging.LogEventLevel.Debug, "MonoMac", this, "ModalDisposable disposed");
                 _impl.Window.OrderOut(_impl.Window);
+                NSApplication.SharedApplication.EndModalSession(_modalSession);
+                disposed = true;
             }
         }
 
         public IDisposable ShowDialog()
         {
-            //TODO: Investigate how to return immediately. 
-            // May be add some magic to our run loop or something
-            NSApplication.SharedApplication.RunModalForWindow(Window);
-            return new ModalDisposable(this);
+            var session = NSApplication.SharedApplication.BeginModalSession(Window);
+            var disposable = new ModalDisposable(this, session);
+            Dispatcher.UIThread.Post(disposable.Continue, DispatcherPriority.ContextIdle);
+
+            return disposable;
         }
     }
-}
+}