@Override
 public void onReceiveAd(Ad arg0) {
   if (listener != null) listener.onReceivedAd();
 }
 @Override
 public void onPresentScreen(Ad arg0) {
   if (listener != null) listener.onPresentScreen();
 }
 @Override
 public void onFailedToReceiveAd(Ad arg0, ErrorCode arg1) {
   if (listener != null) listener.onFailedToReceiveAd();
 }
 @Override
 public void onLeaveApplication(Ad arg0) {
   if (listener != null) listener.onLeaveApplication();
 }
 @Override
 public void onDismissScreen(Ad arg0) {
   if (listener != null) listener.onDismissScreen();
 }