1  隐藏和显示回到顶部按钮

假设有个RecylerView rvHome;有个adapter 

rvHome.setAdapter(new HomeFragmentAdapter(mContext, result));
GridLayoutManager manager = new GridLayoutManager(mContext, 1);
//设置滑动到哪个位置了的监听
manager.setSpanSizeLookup(new GridLayoutManager.SpanSizeLookup() {
    @Override
    public int getSpanSize(int position) {
        if(position<=3){
            ib_top.setVisibility(View.GONE);
        }else {
            ib_top.setVisibility(View.VISIBLE);
        }
        return 1;//只能返回1
    }
});
rvHome.setLayoutManager(manager);//设置只为一列

2 设置点击回到顶部

假设有个图片按钮点击ib_top

ib_top.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        //回到顶部
        rvHome.scrollToPosition(0);
    }
});