Flutter实现底部导航栏效果

class MyApp extends StatelessWidget { // This widget is the root of your application. @override Widget build(BuildContext context) {  return new MaterialApp(   title: 'Flutter Demo',   theme: new ThemeData(    primarySwatch: themeColor(),   ),   home: new MyHomePage(title: 'Flutter Demo Home Page'),  ); }}

class _MyHomePageState extends State<MyHomePage> { PageController pageController; int page = 0; @override Widget build(BuildContext context) {  return new Scaffold(   backgroundColor: Colors.grey,   body: new PageView(     children: [      new Index(),      new Classify(),      new Shopping(),      new Myself()     ],     controller: pageController,     onPageChanged: onPageChanged   ),   bottomNavigationBar: new BottomNavigationBar(items: [    new BottomNavigationBarItem(     icon: new Icon(Icons.laptop_chromebook),     title: new Text("主页"),     backgroundColor: Colors.grey    ),    new BottomNavigationBarItem(      icon: new Icon(Icons.list), title: new Text("分类"),backgroundColor: Colors.grey),    new BottomNavigationBarItem(      icon: new Icon(Icons.local_grocery_store), title: new Text("购物车")),    new BottomNavigationBarItem(icon: new Icon(Icons.person), title: new Text("我的"))   ],     onTap: onTap,     currentIndex: page   ),  ); } @override void initState() {  super.initState();  pageController = new PageController(initialPage: this.page); } void onTap(int index) {  pageController.animateToPage(    index, duration: const Duration(milliseconds: 300),    curve: Curves.ease); } void onPageChanged(int page) {  setState(() {   this.page = page;  }); }}

import 'package:flutter/material.dart';class Classify extends StatelessWidget { @override Widget build(BuildContext context) {  // TODO: implement build  return new Scaffold(   body: new Center(    child:    new Text("分类"),   ),  ); }}