code: private void animateIndicatorInvalidate() {
          if (mIndicatorScroller.computeScrollOffset()) {
              mIndicatorOffset = mIndicatorScroller.getCurr();
              invalidate();
  
              if (!mIndicatorScroller.isFinished()) {
                  postOnAnimation(mIndicatorRunnable);
                  return;
              }
          }
  
          completeAnimatingIndicator();
      }
docs: Callback when each frame in the indicator animation should be drawn.