Apply design properties to tollevel

src/Perspex.Application/Designer/Design.cs

@@ -49,24 +49,15 @@ namespace Perspex
         {
             return control.GetValue(DataContextProperty);
         }
-
-        static Design()
-        {
-            WidthProperty.Changed.Subscribe(OnChanged);
-            HeightProperty.Changed.Subscribe(OnChanged);
-            DataContextProperty.Changed.Subscribe(OnChanged);
-        }
-
-        static void OnChanged(PerspexPropertyChangedEventArgs args)
-        {
-            if(!IsDesignMode)
-                return;
-            if (args.Property == WidthProperty)
-                ((Control) args.Sender).Width = (double) args.NewValue;
-            if (args.Property == HeightProperty)
-                ((Control)args.Sender).Height = (double)args.NewValue;
-            if (args.Property == DataContextProperty)
-                ((Control) args.Sender).DataContext = args.NewValue;
+        
+        internal static void ApplyDesignerProperties(Control target, Control source)
+        {
+            if (source.IsSet(WidthProperty))
+                target.Width = source.GetValue(WidthProperty);
+            if (source.IsSet(HeightProperty))
+                target.Height = source.GetValue(HeightProperty);
+            if (source.IsSet(DataContextProperty))
+                target.DataContext = source.GetValue(DataContextProperty);
         }
     }
 }

src/Perspex.Application/Designer/DesignerAssist.cs

@@ -60,18 +60,20 @@ namespace Perspex.DesignerSupport
         {
 
             Window window;
+            Control original;
             using (PlatformManager.DesignerMode())
             {
-                var obj = ((XamlXmlLoader)new PerspexXamlLoader()).Load(new MemoryStream(Encoding.UTF8.GetBytes(xaml)));
-                window = obj as Window;
+                original =(Control)((XamlXmlLoader)new PerspexXamlLoader()).Load(new MemoryStream(Encoding.UTF8.GetBytes(xaml)));
+                window = original as Window;
                 if (window == null)
                 {
-                    window = new Window() {Content = obj};
+                    window = new Window() {Content = original};
                 }
             }
             s_currentWindow?.Close();
             s_currentWindow = window;
             window.Show();
+            Design.ApplyDesignerProperties(window, original);
             Api.OnWindowCreated?.Invoke(window.PlatformImpl.Handle.Handle);
             Api.OnResize?.Invoke();
         }