code: public void playSequentially(List<Animator> items) {
          if (items != null && items.size() > 0) {
              mNeedsSort = true;
              if (items.size() == 1) {
                  play(items.get(0));
              } else {
                  for (int i = 0; i < items.size() - 1; ++i) {
                      play(items.get(i)).before(items.get(i+1));
                  }
              }
          }
      }
docs: Sets up this AnimatorSet to play each of the supplied animations when the
  previous animation ends.
  
  @param items The animations that will be started one after another.