code: public void scrollOnce() {
          PagerAdapter adapter = getAdapter();
          int currentItem = getCurrentItem();
          int totalCount;
          if (adapter == null || (totalCount = adapter.getCount()) <= 1) {
              return;
          }
  
          int nextItem = (direction == LEFT) ? --currentItem : ++currentItem;
          if (nextItem < 0) {
              if (isCycle) {
                  setCurrentItem(totalCount - 1, isBorderAnimation);
              }
          } else if (nextItem == totalCount) {
              if (isCycle) {
                  setCurrentItem(0, isBorderAnimation);
              }
          } else {
              setCurrentItem(nextItem, true);
          }
      }
docs: scroll only once