Merge pull request #926 from Nice3point/development_fix674

Fix issue 674: Dragging no longer works when SizeToContent is set on Window

src/Wpf.Ui/Controls/TitleBar/TitleBar.cs

@@ -446,11 +446,7 @@ protected virtual void OnLoaded(object sender, RoutedEventArgs e)
         _currentWindow =
             System.Windows.Window.GetWindow(this) ?? throw new ArgumentNullException("Window is null");
         _currentWindow.StateChanged += OnParentWindowStateChanged;
-
-        var handle = new WindowInteropHelper(_currentWindow).EnsureHandle();
-        var windowSource =
-            HwndSource.FromHwnd(handle) ?? throw new ArgumentNullException("Window source is null");
-        windowSource.AddHook(HwndSourceHook);
+        _currentWindow.ContentRendered += OnWindowContentRendered;
     }
 
     private void OnUnloaded(object sender, RoutedEventArgs e)
@@ -583,6 +579,19 @@ private void OnTemplateButtonClick(TitleBarButtonType buttonType)
         }
     }
 
+    /// <summary>
+    ///     Listening window hooks after rendering window content to SizeToContent support
+    /// </summary>
+    private void OnWindowContentRendered(object sender, EventArgs e)
+    {
+        var window = (Window)sender;
+        window.ContentRendered -= OnWindowContentRendered;
+
+        var handle = new WindowInteropHelper(window).Handle;
+        var windowSource = HwndSource.FromHwnd(handle) ?? throw new ArgumentNullException("Window source is null");
+        windowSource.AddHook(HwndSourceHook);
+    }
+
     private IntPtr HwndSourceHook(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled)
     {
         var message = (User32.WM)msg;