Flutter实现底部导航

import 'package:flutter/material.dart';import './views/firstPage.dart';import './views/secondPage.dart';import './views/thirdPage.dart';//首先导入三个界面void main() { runApp(new MyApp());}class MyApp extends StatefulWidget { @override _MyHomePageState createState() => new _MyHomePageState();}class _MyHomePageState extends State<MyApp> with TickerProviderStateMixin{ int _tabIndex = 0; List<BottomNavigationBarItem> _navigationViews; var appBarTitles = ['首页', '发现', '我的']; PageController pageController; var _body; initData() {  _body = new IndexedStack(   children: <Widget>[new FirstPage(), new SecondPage(), new ThirdPage()],   index: _tabIndex,  ); } @override void initState() {  super.initState();  _navigationViews = <BottomNavigationBarItem>[   new BottomNavigationBarItem(    icon: const Icon(Icons.home),    title: new Text(appBarTitles[0]),    backgroundColor: Colors.blue,   ),   new BottomNavigationBarItem(    icon: const Icon(Icons.widgets),    title: new Text(appBarTitles[1]),    backgroundColor: Colors.blue,   ),   new BottomNavigationBarItem(    icon: const Icon(Icons.person),    title: new Text(appBarTitles[2]),    backgroundColor: Colors.blue,   ),  ]; } final navigatorKey = GlobalKey<NavigatorState>(); @override Widget build(BuildContext context) {  initData();  return new MaterialApp(   navigatorKey: navigatorKey,   theme: new ThemeData(     primaryColor: Colors.blue,     accentColor: Colors.blue   ),   home: new Scaffold(    appBar: new AppBar(     title: new Text(      appBarTitles[_tabIndex],      style: new TextStyle(color: Colors.white),     ),    ),    body: _body,    bottomNavigationBar: new BottomNavigationBar(     items: _navigationViews       .map((BottomNavigationBarItem navigationView) => navigationView)       .toList(),     currentIndex: _tabIndex,     type: BottomNavigationBarType.fixed,     onTap: (index) {      setState(() {       _tabIndex = index;      });     },    ),   ),  ); }}

import 'package:flutter/material.dart';class FirstPage extends StatefulWidget { @override State<StatefulWidget> createState() => new FirstPageState();}class FirstPageState extends State<FirstPage> { @override Widget build(BuildContext context) {  return new Scaffold(   body: new Center(    child: new Text('这是第一个界面'),   ),  ); }}

import 'package:flutter/material.dart';class SecondPage extends StatefulWidget { @override State<StatefulWidget> createState() => SecondPageState();}class SecondPageState extends State<SecondPage> { @override Widget build(BuildContext context) {  return new Scaffold(   body: new Center(    child: new Text("这是我第二个页面"),   ),  ); }}

import 'package:flutter/material.dart';class ThirdPage extends StatefulWidget { @override State<StatefulWidget> createState() => ThirdPageState();}class ThirdPageState extends State<ThirdPage>{ @override Widget build(BuildContext context) {  return new Scaffold(   body: new Center(    child: new Text('我是界面三'),   ),  ); }}