flutter 导航栏 BottomNavigationBar底部导航栏相当于iOS tabbar

//main.dart文件
import 'package:flutter/material.dart';
import 'package:myapp/Tabbar.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  //过时了const MyApp({Key key}) : super(key: key);
//现在用这个

const MyApp({super.key});


  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Tabbar(),
    );
  }
}

//Tabbar.dart文件
import 'package:flutter/material.dart';
import './Home.dart';
import './Category.dart';
import './Setting.dart';

class Tabbar extends StatefulWidget {
  Tabbar({Key key}) : super(key: key);

  _TabbarState createState() => _TabbarState();
}

class _TabbarState extends State<Tabbar> {
  int _tabbarIndex = 0;//用于记录当前选中第几个item
  List _tabPages = [//装载底部tabbar的item所对应的页面
    HomePage(),
    CategoryPage(),
    SettingPage()
  ];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("appbarTitle"),
      ),
      body: this._tabPages[this._tabbarIndex],//显示当前选中的tabbatItem所对应的页面
      bottomNavigationBar: BottomNavigationBar(
        iconSize: 36,
        fixedColor: Colors.pink,
        type: BottomNavigationBarType.fixed,
        currentIndex: this._tabbarIndex,//当前选中第几个item
        onTap: (index){//点击回调
          setState(() {//当需要改变页面中的参数值的时候，需要在该方法中更新数据，否则不会刷新页面
            this._tabbarIndex = index;
          });
        },
        items: [//配置底部导航栏的按钮列表
          BottomNavigationBarItem(icon: Icon(Icons.home), title: Text("首页")),
          BottomNavigationBarItem(
              icon: Icon(Icons.category), title: Text("分类")),
          BottomNavigationBarItem(
              icon: Icon(Icons.settings), title: Text("设置")),
        ],
      ),
    );
  }
}

//首页  Home.dart
import 'package:flutter/material.dart';

class HomePage extends StatelessWidget {
  const HomePage({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Container(
      child: Text('首页'),
    );
  }
}

//分类 Category.dart
import 'package:flutter/material.dart';

class CategoryPage extends StatelessWidget {
  const CategoryPage({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Container(
        child: Text('分类')
    );
  }
}

//设置 Setting.dart
import 'package:flutter/material.dart';

class CategoryPage extends StatelessWidget {
  const CategoryPage({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Container(
        child: Text('分类')
    );
  }
}