attachToViewPager 中没有判断 itemCount 为零的情况

[thebitmin]

public void attachToViewPager(ViewPager viewPager) {
        this.viewPager = viewPager;
        PagerAdapter pagerAdapter = viewPager.getAdapter();
        if (pagerAdapter != null) {
            //TODO 如果项目使用了阿里开源库，UltraViewPager，想要兼容需要用以下方式获取 itemCount，否则去除这个if条件
            if (pagerAdapter instanceof UltraViewPagerAdapter) {
                //从UltraViewPagerAdapter获取真实的个数
                itemCount = ((UltraViewPagerAdapter) pagerAdapter).getRealCount();
            } else {
                itemCount = pagerAdapter.getCount();
            }
            selection = viewPager.getCurrentItem() % itemCount;
            checkItemCount();
        }

        viewPager.addOnPageChangeListener(this);
    }

[thebitmin]

@Override
    public void onPageSelected(int i) {
        if (viewPager != null) {
            PagerAdapter pagerAdapter = viewPager.getAdapter();
            if (pagerAdapter != null) {
                selection = viewPager.getCurrentItem() % itemCount;
            }
        }
        postInvalidate();
    }