private void addButtonsCallback() {
      if (positiveDialogListener != null || negativeDialogListener != null) {
        builder.callback(
            new MaterialDialog.ButtonCallback() {
              @Override
              public void onNeutral(MaterialDialog dialog) {
                if (neutralDialogListener != null) {
                  neutralDialogListener.onClick(dialog, DialogInterface.BUTTON_NEUTRAL);
                }
              }

              @Override
              public void onPositive(MaterialDialog dialog) {
                if (positiveDialogListener != null) {
                  positiveDialogListener.onClick(dialog, DialogInterface.BUTTON_POSITIVE);
                }
              }

              @Override
              public void onNegative(MaterialDialog dialog) {
                if (negativeDialogListener != null) {
                  negativeDialogListener.onClick(dialog, DialogInterface.BUTTON_NEGATIVE);
                }
              }
            });
      }
    }