private void _tviMessageList_MouseDoubleClick(object sender, MouseButtonEventArgs e)
 {
     if (_wndMessage == null)
     {
         _wndMessage         = new MessageListWindow(_appModel);
         _wndMessage.Owner   = Window.GetWindow(this);
         _wndMessage.Closed += _wndMessage_Closed;
         _wndMessage.Show();
     }
     else
     {
         _wndMessage.Activate();
         _wndMessage.Topmost = true;
         _wndMessage.Topmost = false;
         _wndMessage.Focus();
     }
 }
 private void _wndMessage_Closed(object sender, EventArgs e)
 {
     _wndMessage = null;
 }