public void OnDrageLeave()
 {
     if (_overlayWindow != null)
     {
         _overlayWindow.Close();
         _overlayWindow = null;
     }
 }
 public void OnDragEnter()
 {
     if (_overlayWindow == null)
     {
         _overlayWindow = new DropOverlayWindow();
     }
     if (this.WindowState == System.Windows.WindowState.Maximized)
     {
         _overlayWindow.Left = 0;
         _overlayWindow.Top  = 0;
     }
     else
     {
         _overlayWindow.Left = this.Left;
         _overlayWindow.Top  = this.Top;
     }
     _overlayWindow.Width   = this.ActualWidth;
     _overlayWindow.Height  = this.ActualHeight;
     _overlayWindow.Topmost = true;
     _overlayWindow.Show();
 }