Now showing exception happened inside designer process when parsing xaml

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

@@ -46,11 +46,19 @@ namespace Perspex.Designer.AppHost
         {
             if(!_initSuccess)
                 return;
-            dynamic window = Activator.CreateInstance(LookupType("Perspex.Controls.Window"));
-            _xamlReader(new MemoryStream(Encoding.UTF8.GetBytes(xaml)), window);
-            var hWnd = (IntPtr) window.PlatformImpl.Handle;
-            _host.SetWindow(hWnd);
-            window.Show();
+            try
+            {
+                dynamic window = Activator.CreateInstance(LookupType("Perspex.Controls.Window"));
+                _xamlReader(new MemoryStream(Encoding.UTF8.GetBytes(xaml)), window);
+                var hWnd = (IntPtr) window.PlatformImpl.Handle;
+                _host.SetWindow(hWnd);
+                window.Show();
+            }
+            catch(Exception e)
+            {
+               _host.SetWindow(IntPtr.Zero);
+               _host.PlaceholderText = e.ToString();
+            }
         }
 
         void UpdateState(string state)

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

@@ -13,26 +13,43 @@ namespace Perspex.Designer.AppHost
     {
         public WindowHost()
         {
-            SetStyle(ControlStyles.AllPaintingInWmPaint, true);
+            BackColor = Color.AliceBlue;
+            _textBox = new TextBox {Dock = DockStyle.Fill, ReadOnly = true, Multiline = true, Visible = false};
+            Controls.Add(_textBox);
         }
+        
+        private IntPtr _hWnd;
+        private TextBox _textBox;
 
-        protected override void OnPaint(PaintEventArgs e)
+        public string PlaceholderText
         {
-            e.Graphics.FillRectangle(Brushes.AliceBlue, ClientRectangle);
+            get { return _textBox.Text; }
+            set
+            {
+                _textBox.Text = value;
+                FixWindow();
+            }
         }
 
-        private IntPtr _hWnd;
+        
 
         public void SetWindow(IntPtr hWnd)
         {
+            if (_hWnd != IntPtr.Zero)
+                WinApi.SendMessage(_hWnd, WinApi.WM_CLOSE, IntPtr.Zero, IntPtr.Zero);
             _hWnd = hWnd;
-            WinApi.SetParent(hWnd, Handle);
-            FixWindow();
+            if (_hWnd != IntPtr.Zero)
+            {
+                WinApi.SetParent(hWnd, Handle);
+                FixWindow();
+            }
         }
 
         void FixWindow()
         {
-            WinApi.MoveWindow(_hWnd, 0, 0, Width, Height, true);
+            if (_hWnd != IntPtr.Zero)
+                WinApi.MoveWindow(_hWnd, 0, 0, Width, Height, true);
+            _textBox.Visible = _hWnd == IntPtr.Zero && !string.IsNullOrWhiteSpace(_textBox.Text);
         }
 
         protected override void OnResize(EventArgs e)

src/Windows/Perspex.Designer/Comm/ProcessHost.cs

@@ -65,6 +65,7 @@ namespace Perspex.Designer.Comm
         void OnExited(object sender, EventArgs eventArgs)
         {
             _comm.Dispose();
+            _proc = null;
             _dispatcher.Post(_ =>
             {
                 IsAlive = false;
@@ -78,7 +79,11 @@ namespace Perspex.Designer.Comm
             if (_proc != null)
             {
                 _proc.Exited -= OnExited;
-                _proc.Kill();
+                try
+                {
+                    _proc.Kill();
+                }
+                catch { }
                 OnExited(null, null);
                 State = "Restarting...";
             }

src/Windows/Perspex.Designer/WinApi.cs

@@ -13,5 +13,10 @@ namespace Perspex.Designer
         public static extern bool MoveWindow(IntPtr hWnd, int X, int Y, int nWidth, int nHeight, bool bRepaint);
         [DllImport("user32.dll")]
         public static extern bool SetParent(IntPtr hWnd, IntPtr hWndNewParent);
+        [DllImport("user32.dll", CharSet = CharSet.Auto)]
+        public static extern IntPtr SendMessage(IntPtr hWnd, uint Msg, IntPtr wParam, IntPtr lParam);
+
+        public const uint WM_CLOSE = 0x0010;
+
     }
 }