WndHost is unreliable

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

@@ -11,13 +11,18 @@ namespace Perspex.Designer.AppHost
 {
     class WindowHost : UserControl
     {
-        public WindowHost()
+        private readonly bool _supportScroll;
+
+        public WindowHost(bool supportScroll)
         {
-            AutoScroll = true;
-            VerticalScroll.Enabled = true;
-            HorizontalScroll.Enabled = true;
+            _supportScroll = supportScroll;
+            if (_supportScroll)
+            {
+                AutoScroll = true;
+                VerticalScroll.Enabled = true;
+                HorizontalScroll.Enabled = true;
+            }
             SetStyle(ControlStyles.AllPaintingInWmPaint, true);
-            Text = "ScrollableArea";
             Controls.Add(_windowHost);
             _windowHost.Anchor = AnchorStyles.None;
             _timer.Tick += delegate
@@ -102,25 +107,36 @@ namespace Perspex.Designer.AppHost
         {
             if (_hWnd != IntPtr.Zero)
             {
-                WinApi.RECT rc;
-                WinApi.GetWindowRect(_hWnd, out rc);
-                _desiredWidth = rc.Right - rc.Left;
-                _desiredHeight = rc.Bottom - rc.Top;
-                var pt = _windowHost.PointToClient(new Point(rc.Left, rc.Top));
+                if (_supportScroll)
+                {
+                    WinApi.RECT rc;
+                    WinApi.GetWindowRect(_hWnd, out rc);
+                    _desiredWidth = rc.Right - rc.Left;
+                    _desiredHeight = rc.Bottom - rc.Top;
+                    var pt = _windowHost.PointToClient(new Point(rc.Left, rc.Top));
 
-                if (!(pt.Y == 0 && pt.X == 0 && _desiredWidth == _windowHost.Width && _desiredHeight == _windowHost.Height))
+                    if (
+                        !(pt.Y == 0 && pt.X == 0 && _desiredWidth == _windowHost.Width &&
+                          _desiredHeight == _windowHost.Height))
+                    {
+                        _windowHost.Width = _desiredWidth;
+                        _windowHost.Height = _desiredHeight;
+                        WinApi.MoveWindow(_hWnd, 0, 0, _desiredWidth, _desiredHeight, true);
+                    }
+                    FixPosition();
+                }
+                else
                 {
-                    _windowHost.Width = _desiredWidth;
-                    _windowHost.Height = _desiredHeight;
-                    WinApi.MoveWindow(_hWnd, 0, 0, _desiredWidth, _desiredHeight, true);
+                    _windowHost.Width = Width;
+                    _windowHost.Height = Height;
+                    WinApi.MoveWindow(_hWnd, 0, 0, Width, Height, true);
                 }
-                FixPosition();
             }
         }
 
         protected override void OnResize(EventArgs e)
         {
-            FixPosition();
+            FixWindow();
             base.OnResize(e);
         }
     }

src/Windows/Perspex.Designer/InProcDesigner/InProcDesignerView.xaml.cs

@@ -33,7 +33,7 @@ namespace Perspex.Designer.InProcDesigner
             InitializeComponent();
             DataContext = _appModel;
             _appModel.PropertyChanged += ModelPropertyChanged;
-            WindowHostControl.Child = _host = new WindowHost();
+            WindowHostControl.Child = _host = new WindowHost(true);
             HandleVisibility();
             HandleWindow();
 

src/Windows/Perspex.Designer/PerspexDesigner.xaml

@@ -6,7 +6,7 @@
              mc:Ignorable="d" 
              d:DesignHeight="300" d:DesignWidth="300">
     <Grid>
-        <ContentControl x:Name="NativeContainer" Panel.ZIndex="1"/> 
+        <WindowsFormsHost Background="White" x:Name="NativeContainer" Panel.ZIndex="1"/> 
         <ScrollViewer VerticalScrollBarVisibility="Auto" Panel.ZIndex="0">
             <TextBox IsReadOnly="True" TextWrapping="WrapWithOverflow" x:Name="State"/>
         </ScrollViewer>

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

@@ -73,41 +73,19 @@ namespace Perspex.Designer
         {
             if (e.PropertyName == nameof(ProcessHost.WindowHandle))
             {
-                if (NativeContainer.Content != null)
+                if (NativeContainer.Child == null)
                 {
-                    var wndHost = ((HwndHost) NativeContainer.Content);
-                    NativeContainer.Content = null;
-                    wndHost?.Dispose();
+                    NativeContainer.Child = new WindowHost(false);
                 }
-                if (_host.WindowHandle != IntPtr.Zero)
                 {
-                    var host = new NativeWindowHost(_host.WindowHandle);
-                    NativeContainer.Content = host;
+                    var wndHost = ((WindowHost) NativeContainer.Child);
+                    wndHost.SetWindow(_host.WindowHandle);
                 }
-            }
-        }
-
-        class NativeWindowHost  :HwndHost
-        {
-            private readonly IntPtr _hWnd;
-
-            public NativeWindowHost(IntPtr hWnd)
-            {
-                _hWnd = hWnd;
-            }
-
-            protected override HandleRef BuildWindowCore(HandleRef hwndParent)
-            {
-                WinApi.SetParent(_hWnd, hwndParent.Handle);
-                return new HandleRef(this, _hWnd);
-            }
 
-            protected override void DestroyWindowCore(HandleRef hwnd)
-            {
-                WinApi.SendMessage(hwnd.Handle, WinApi.WM_CLOSE, IntPtr.Zero, IntPtr.Zero);
             }
         }
 
+
         public void KillProcess()
         {
             _host.Kill();