docs: @Override
      public void onReceive(Context context, Intent notification) {
          GoogleCloudMessaging gcm = GoogleCloudMessaging.getInstance(context);
          String messageType = gcm.getMessageType(notification);
          Bundle extras = notification.getExtras();
  
          if (!extras.isEmpty() && GoogleCloudMessaging.MESSAGE_TYPE_MESSAGE.equals(messageType)) {
              showNotification(context, extras);
          }
      }