private void MainWindow_OnLoaded(object sender, RoutedEventArgs e)
 {
     var loginWindow = new LoginDialog();
     loginWindow.Owner = this;
     loginWindow.WindowStartupLocation = WindowStartupLocation.CenterOwner;
     loginWindow.ShowDialog();
     if (loginWindow.LoggedIn)
     {
         ButtonSend.IsEnabled = true;
         client.DataMessageArrived += ClientOnDataMessageArrived;
         SessionId = loginWindow.SessionId;
     }
 }