Android悬浮按钮点击返回顶部FloatingActionButton

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  xmlns:app="http://schemas.android.com/apk/res-auto">
  <ListView
    android:id="@+id/listview_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />
  <android.support.design.widget.FloatingActionButton
    android:id="@+id/floating_btn_main"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentRight="true"
    android:layout_alignParentBottom="true"
    android:src="@mipmap/top"
    app:elevation="10dp"
    android:layout_margin="15dp"/>
</RelativeLayout>

package com.duanlian.floatingbtn;

import android.support.design.widget.FloatingActionButton;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.ListView;

import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {
  private ListView mListView;
  private FloatingActionButton mFloatBtn;
  private MyListViewAdapter mAdapter;
  private List<String> mList;


  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    initView();

  }
  private void initView() {
    mListView = (ListView) findViewById(R.id.listview_main);
    mFloatBtn = (FloatingActionButton) findViewById(R.id.floating_btn_main);
    mList = new ArrayList<>();
    for (int i = 0; i < 30; i++) {
      mList.add(i + "");
    }
    mAdapter = new MyListViewAdapter(this, mList);
    mListView.setAdapter(mAdapter);
    //悬浮按钮的点击事件的监听
    mFloatBtn.setOnClickListener(new View.OnClickListener() {
      @Override
      public void onClick(View view) {
        //listView返回到顶部
        mListView.smoothScrollToPosition(0);
      }
    });
  }
}