Designer positioning fixes

src/Windows/Perspex.Designer/AppHost/WindowHost.cs

@@ -25,6 +25,8 @@ namespace Perspex.Designer.AppHost
             SetStyle(ControlStyles.AllPaintingInWmPaint, true);
             Controls.Add(_windowHost);
             _windowHost.Anchor = AnchorStyles.None;
+            if (!supportScroll)
+                _windowHost.Visible = false;
             _timer.Tick += delegate
             {
                 ReloadSettings();
@@ -98,7 +100,7 @@ namespace Perspex.Designer.AppHost
             _hWnd = hWnd;
             if (_hWnd != IntPtr.Zero)
             {
-                WinApi.SetParent(hWnd, _windowHost.Handle);
+                WinApi.SetParent(hWnd, _supportScroll ? _windowHost.Handle : Handle);
                 FixWindow();
             }
         }
@@ -127,8 +129,6 @@ namespace Perspex.Designer.AppHost
                 }
                 else
                 {
-                    _windowHost.Width = Width;
-                    _windowHost.Height = Height;
                     WinApi.MoveWindow(_hWnd, 0, 0, Width, Height, true);
                 }
             }

src/Windows/Perspex.Designer/PerspexDesigner.xaml.cs

@@ -73,14 +73,16 @@ namespace Perspex.Designer
         {
             if (e.PropertyName == nameof(ProcessHost.WindowHandle))
             {
-                if (NativeContainer.Child == null)
+                if (NativeContainer.Child != null)
                 {
-                    NativeContainer.Child = new WindowHost(false);
-                }
-                {
-                    var wndHost = ((WindowHost) NativeContainer.Child);
-                    wndHost.SetWindow(_host.WindowHandle);
+                    var child = NativeContainer.Child;
+                    NativeContainer.Child = null;
+                    child.Dispose();
                 }
+                NativeContainer.Child = new WindowHost(false);
+                var wndHost = ((WindowHost) NativeContainer.Child);
+                wndHost.SetWindow(_host.WindowHandle);
+
 
             }
         }