private void getLastMsgBt_Click(object sender, RoutedEventArgs e) { int nb = -1; try { nb = int.Parse(nbLastMsgTbx.Text); } catch (Exception) { } if (nb > 0) { client.GetLastMessages(actorTbx.Text, nb, callback); } else { client.GetLastMessages(actorTbx.Text, callback); } }