Recyclerview的getChildAt(position)方法获取可见第一条的view返回null；

使用Recyclerview的getChildAt(position)方法获取可见第一条的view，总是null；

使用LinearLayoutManager的findViewByPosition(position)方法解决此问题。

使用LinearLayoutManager的scrollToPositionWithOffset（position，offset）来定位到指定位置。

public void savePositionState(){
int firstVisibleItemPosition = mLinearLayoutManager.findFirstVisibleItemPosition();
mPositionState[0] = firstVisibleItemPosition;
//        View view = mRecyclerView.getChildAt(firstVisibleItemPosition);
View view = mLinearLayoutManager.findViewByPosition(firstVisibleItemPosition);
if (view != null) {
int top = view.getTop();
mPositionState[1] = top;
}

DebugLog.d(TAG,"InfoStream_savePositionState mPositionState[0]:"+mPositionState[0]+" mPositionState[1]:"+mPositionState[1]);
}

public void restorePosistionState(){
DebugLog.d(TAG,"InfoStream_restorePosistionState mPositionState[0]:"+mPositionState[0]+" mPositionState[1]:"+mPositionState[1]);
mLinearLayoutManager.scrollToPositionWithOffset(mPositionState[0], mPositionState[1]);
mFirstCompletelyVisibleItemPosition = mLinearLayoutManager.findFirstCompletelyVisibleItemPosition();
}