import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget{
 @override
 Widget build(BuildContext context) {
  return MaterialApp(
   home: Scaffold(
    body: MyHomePage(),
   ),
  );
 }
}
class MyHomePage extends StatefulWidget{
 MyHomePage({Key key}) : super(key:key);
 @override
 _MyHomePageState createState() => _MyHomePageState();
 @override
 Widget build(BuildContext context) {
  // TODO: implement build
  return null;
 }
}
class _MyHomePageState extends State<MyHomePage>
{
 int _selectedIndex = 1;//当前选中项的索引
 final _widgetOptions = [
  Text('Index 0: 微信'),
  Text('Index 1: 通讯录'),
  Text('Index 2: 发现'),
  Text('Index 3：我')
 ];
 @override
 Widget build(BuildContext context) {
  return Scaffold(
   appBar: AppBar(
    title: Text('仿微信'),
   ),
   body: Center(
    child: _widgetOptions.elementAt(_selectedIndex),//居中显示某个文本
   ),
   //底部导航按钮,包含图标及文本
   bottomNavigationBar: BottomNavigationBar(
    items: <BottomNavigationBarItem>[
     BottomNavigationBarItem(icon: Icon(Icons.chat),backgroundColor:Colors.green,title: Text('微信')),//设置背景颜色和icon的描述
     BottomNavigationBarItem(icon: Icon(Icons.contacts),backgroundColor:Colors.green,title: Text('通讯录')),
     BottomNavigationBarItem(icon: Icon(Icons.account_circle),backgroundColor:Colors.green,title: Text('发现')),
     BottomNavigationBarItem(icon: Icon(Icons.memory),backgroundColor:Colors.green,title: Text('我')),
     ],
//    backgroundColor: Colors.green,
    currentIndex: _selectedIndex,//当前选中项的索引
    fixedColor: Colors.deepPurple,//选项中项的颜色
    onTap:_onItemTapped,//选择按下处理
   ),
  );
 }
 //选择按下处理
void _onItemTapped(int index)
{
 setState(() {
  _selectedIndex = index;
 });
}
}