直接使用 smoothScrollToPosition(position) 时，如果要定位的数据在集合下半部分，则滚动结束后，需要显示的数据是在手机界面地步
可以使用
((LinearLayoutManager) ((RecyclerView)getView(R.id.rv)).getLayoutManager()).scrollToPositionWithOffset(position, 0)
达到每次滚动结束，数据都是在顶部显示，但是数据不是平滑滚动的。
如果要实现不论哪种情况，都能让数据平滑滚动到顶部显示，需要重写
LinearLayoutManager
1，覆写 LinearSmoothScroller
public class TopLinearSmoothScroller extends LinearSmoothScroller {
public TopLinearSmoothScroller(Context context) {
super(context);
@Override
public int getVerticalSnapPreference() {
return SNAP_TO_START;
2，重写 recyclerview.LinearLayoutManager 的 smoothScrollToPosition 方法
TopLinearSmoothScroller scroller = new TopLinearSmoothScroller(rv.getContext());
LinearLayoutManager layoutManager = new LinearLayoutManager(context) {
@Override
public void smoothScrollToPosition(RecyclerView recyclerView, RecyclerView.State state, int position) {
super.smoothScrollToPosition(recyclerView, state, position);
scroller.setTargetPosition(position);
startSmoothScroll(scroller);
rv.setLayoutManager(layoutManager);
3，最后调用 smoothScrollToPosition 即可
rv.smoothScrollToPosition(position);
