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);      }    });  }}