RecyclerView使用——点击按钮返回顶部

recyclerView下滑到某个position,按钮显示,点击按钮返回recyclerView的顶部;

1.xml布局:

<ImageView
        android:id="@+id/iv_batch_top"
        android:layout_width="40dp"
        android:layout_height="40dp"
        android:src="@mipmap/fragment_batch_back" />

2.position>20时,将按钮显示;小于等于则隐藏;

private RecyclerView mFolderRv;
....
   GridLayoutManager llm = new GridLayoutManager(getMainActivity(), 1);
        llm.setSpanSizeLookup(new GridLayoutManager.SpanSizeLookup() {
            @Override
            public int getSpanSize(int i) {
                if (i <= 20) {
                    mBackTopIv.setVisibility(View.GONE);
                } else {
                    mBackTopIv.setVisibility(View.VISIBLE);
                }
                return 1;//返回 1
            }
        });
        mFolderRv.setLayoutManager(llm);

3.按钮的点击事件:

....
case R.id.iv_import_top:
                mFolderRv.scrollToPosition(0);//返回到顶部 即position=0;
                break;
                ...