@Override
 protected void onScrollChanged(int l, int t, int oldl, int oldt) {
   super.onScrollChanged(l, t, oldl, oldt);
   if (listener != null) {
     listener.onScrollChanged(this, l, t, oldl, oldt);
   }
 }
 @Override
 protected void onScrollChanged(int l, int t, int oldl, int oldt) {
   super.onScrollChanged(l, t, oldl, oldt);
   listener.onScrollChanged(l, t, oldl, oldt);
 }