return new MATErialApp(   home: new Scaffold(    body: new center(     child: _currentPage // 动态的展示我们当前的页面    ),    bottomNavigationBar: bottomNavigationBar, // 底部工具栏   ),    theme: new ThemeData(   PrimarySwatch: Colors.blue, // 设置主题颜色   ),   );  

 import 'package:flutter/material.dart'; import 'package:flutter_demo/index/index.dart';   // 导入index.dart  // 这里为入口函数 void main() => runApp(new MyApp());  class MyApp extends statelessWidget {  // This widget is the root of your application.  @override  Widget build(BuildContext context) {  return new MaterialApp(   tITle: 'Flutter Demo',   home: new Index(),  // 指定去加载 Index页面。  );  } }

 import 'package:flutter/material.dart';  // 创建一个 Icon 展示控件 class NavigationIconView {   // 创建两个属性，一个是 用来展示 icon， 一个是动画处理  final BottomNavigationBarItem item;  final AnimationController controller;   // 类似于 java 中的构造方法  // 创建 NavigationIconView 需要传入三个参数， icon 图标，title 标题， TickerPRovider  NavigationIconView({Widget icon, Widget title, TickerProvider vsync}):  item = new BottomNavigationBarItem(   icon: icon,   title: title,  ),  controller = new AnimationController(   duration: kThemeAnimationDuration, // 设置动画持续的时间   vsync: vsync       // 默认属性和参数  ); }

 import 'package:flutter/material.dart'; import 'package:flutter_demo/NoticePage/notice_page.dart'; import 'package:flutter_demo/home/home_page.dart'; import 'package:flutter_demo/idea/idea_page.dart'; import 'package:flutter_demo/market/market_page.dart'; import 'package:flutter_demo/my/my_page.dart';  import 'navigation_icon_view.dart'; // 如果是在同一个包的路径下，可以直接使用对应的文件名  // 创建一个 带有状态的 Widget Index class Index extends StatefulWidget {   // 固定的写法  @override  State<StatefulWidget> createstate() => new _IndexState(); }  // 要让主页面 Index 支持动效，要在它的定义中附加mixin类型的对象TickerProviderStateMixin class _IndexState extends State<Index> with TickerProviderStateMixin{   int _currentIndex = 0; // 当前界面的索引值  List<NavigationIconView> _navigationViews; // 底部图标按钮区域  List<StatefulWidget> _pageList; // 用来存放我们的图标对应的页面  StatefulWidget _currentPage; // 当前的显示页面   // 定义一个空的设置状态值的方法  void _rebuild() {  setState((){});  }   @override  void initState() {  suPEr.initState();   // 初始化导航图标  _navigationViews = <NavigationIconView>[   new NavigationIconView(icon: new Icon(Icons.assessment), title: new Text("首页"), vsync: this), // vsync 默认属性和参数   new NavigationIconView(icon: new Icon(Icons.all_inclusive), title: new Text("想法"), vsync: this),   new NavigationIconView(icon: new Icon(Icons.add_shopping_cart), title: new Text("市场"), vsync: this),   new NavigationIconView(icon: new Icon(Icons.add_alert), title: new Text("通知"), vsync: this),   new NavigationIconView(icon: new Icon(Icons.perm_identity), title: new Text("我的"), vsync: this),  ];   // 给每一个按钮区域加上监听  for (NavigationIconView view in _navigationViews) {   view.controller.addListener(_rebuild);  }   // 将我们 bottomBar 上面的按钮图标对应的页面存放起来，方便我们在点击的时候  _pageList = <StatefulWidget>[   new HomePage(),   new IdeaPage(),   new MarketPage(),   new NoticePage(),   new MyPage()  ];  _currentPage = _pageList[_currentIndex];  }   @override  Widget build(BuildContext context) {   // 声明定义一个 底部导航的工具栏  final BottomNavigationBar bottomNavigationBar = new BottomNavigationBar(   items: _navigationViews    .map((NavigationIconView navigationIconView) => navigationIconView.item)    .toList(), // 添加 icon 按钮   currentIndex: _currentIndex, // 当前点击的索引值   type: BottomNavigationBarType.fixed, // 设置底部导航工具栏的类型：fixed 固定   onTap: (int index){ // 添加点击事件   setState((){ // 点击之后，需要触发的逻辑事件    _navigationViews[_currentIndex].controller.reverse();    _currentIndex = index;    _navigationViews[_currentIndex].controller.forward();    _currentPage = _pageList[_currentIndex];   });   },  );   return new MaterialApp(   home: new Scaffold(    body: new Center(     child: _currentPage // 动态的展示我们当前的页面    ),    bottomNavigationBar: bottomNavigationBar, // 底部工具栏   ),    theme: new ThemeData(   primarySwatch: Colors.blue, // 设置主题颜色   ),   );  }  }

 import 'package:flutter/material.dart';  class HomePage extends StatefulWidget{  @override  State<StatefulWidget> createState() => new _HomePageState(); }  class _HomePageState extends State<HomePage> {   @override  Widget build(BuildContext context) {  return new MaterialApp(   home: new Scaffold(   appBar: new AppBar(    title: new Text('首页'),    actions: <Widget>[    new Container()    ],   ),   body: new Center(    child: null,   ),   ),  );  } }

 import 'package:flutter/material.dart';  class IdeaPage extends StatefulWidget{  @override  State<StatefulWidget> createState() => new _IdeaPageState(); } class _IdeaPageState extends State<IdeaPage> {   @override  Widget build(BuildContext context) {  return new MaterialApp(   home: new Scaffold(   appBar: new AppBar(    title: new Text('想法'),    actions: <Widget>[    new Container()    ],   ),   body: new Center(    child: null,   ),   ),  );  } }

 import 'package:flutter/material.dart'; class MarketPage extends StatefulWidget{  @override  State<StatefulWidget> createState() => new _MarketPageState(); } class _MarketPageState extends State<;marketPage> {  @override  Widget build(BuildContext context) {  return new MaterialApp(   home: new Scaffold(   appBar: new AppBar(    title: new Text('市场'),    // 后面的省略    // ......   )   ),  );  }  }