code: @Override
    public void onDismissed(Snackbar snackbar, @DismissEvent int event) {
      if (callback != null) {
        callback.onDismissed(snackbar, event);
      }
    }
docs: Notifies that the Snackbar has been dismissed through some means.
  
  @param snackbar The Snackbar which has been dismissed.
  @param event    The event which caused the dismissal.