RecyclerView 针对于item中的单个view刷新

int fristPos = ((LinearLayoutManager) teacherLive.getLayoutManager()).findFirstVisibleItemPosition();
int lastPos = ((LinearLayoutManager) teacherLive.getLayoutManager()).findLastVisibleItemPosition();
if (i >= fristPos && i <= lastPos) {//如果可见，则刷新一下这条数据
	TeacherLiveAdapter.TeacherLiveViewHolder viewHolder = (TeacherLiveAdapter.TeacherLiveViewHolder) teacherLive.findViewHolderForAdapterPosition(i);
	showCountDown(bean,viewHolder.liveItem);
}