When using RecylerView to display data, a floating button is displayed at the bottom right. Its functions are:

Hide the button when pulling up, show the button when pulling down, and click this button to return to the top. As shown in the picture:

The layout is as follows:

   <!--Without adding CoordinatorLayout，FloatActionButton Will not show-->
<android.support.design.widget.CoordinatorLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent">

        <android.support.v7.widget.RecyclerView
            android:layout_width="match_parent"
            android:id="@+id/recyler_view"
            android:layout_height="match_parent">
        </android.support.v7.widget.RecyclerView>
        <android.support.design.widget.FloatingActionButton
            android:id="@+id/go_up"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="bottom|right"
            app:fabSize="mini"
            android:layout_margin="@dimen/fab_margin"
            android:src="@mipmap/up"
            app:backgroundTint="#FF9800"
            />
</android.support.design.widget.CoordinatorLayout>

Note that the CoordinatorLayout should be covered on the outside, otherwise the FloatingActionButton will not be displayed.

mFloatingActionButton = view.findViewById(R.id.go_up);

Add sliding listening for Recylerview, hide button when pulling up [finger from bottom to top], and display button when sliding down [finger from top to bottom]

 mRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
            @Override
            public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
                super.onScrollStateChanged(recyclerView, newState);
                if (newState == RecyclerView.SCROLL_STATE_IDLE) {
                    if (lastItemPosition + 1 == lm.getItemCount()) {
                        //Log.d(TAG, "I'm loading more");
                        mCurrentStart++;
                        loadMore();
                    }
                }
            }

            @Override
            public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                super.onScrolled(recyclerView, dx, dy);
                lastItemPosition = lm.findLastVisibleItemPosition();
                if (dy > 0 && mFloatingActionButton.getVisibility() == VISIBLE) {
                    mFloatingActionButton.hide();
                } else if (dy < 0 && mFloatingActionButton.getVisibility() != VISIBLE) {
                    mFloatingActionButton.show();
                }
            }
        });

The point is that in the onScrolled method, when you pull up [finger from bottom to top], Dy > 0, and if the button is visible, it will be hidden,

When sliding down, Dy < 0, if the button is not visible, let it display.

It can be realized here. Pull up to hide and slide down to show.

Next, click button to go back to the top
It's simple:

  mFloatingActionButton.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                mRecyclerView.smoothScrollToPosition(0);  //Slide to first
            }
        });

Smoothscroll to positoin() is a sliding process, which is not very abrupt. It has been achieved to this end