1  隱藏和顯示回到頂部按鈕

假設有個RecylerView rvHome;有個adapter 

rvHome.setAdapter(new HomeFragmentAdapter(mContext, result));
GridLayoutManager manager = new GridLayoutManager(mContext, 1);
//設定滑動到哪個位置了的監聽
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);//設定只為一列

假設有個圖片按鈕點選ib_top

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