code: public void setActiveView(View v, int position) {
          final View oldView = mActiveView;
          mActiveView = v;
          mActivePosition = position;
  
          if (mAllowIndicatorAnimation && oldView != null) {
              startAnimatingIndicator();
          }
  
          invalidate();
      }
docs: Set the active view.
  If the mdActiveIndicator attribute is set, this View will have the indicator drawn next to it.
  
  @param v        The active view.
  @param position Optional position, usually used with ListView. v.setTag(R.id.mdActiveViewPosition, position)
  must be called first.