code: @SuppressLint("NewApi")
  	private void postAnimationInvalidate() {
  		if (mScroller.computeScrollOffset()) {
  			final int oldX = (int) mOffsetPixels;
  			final int x = mScroller.getCurrX();
  
  			if (x != oldX) {
  				setOffsetPixels(x);
  			}
  			if (x != mScroller.getFinalX()) {
  				postOnAnimation(mDragRunnable);
  				return;
  			}
  		}
  
  		completeAnimation();
  	}
docs: Callback when each frame in the drawer animation should be drawn.