Flutter:持久化BottomNavigationBar并根据所选的BottomNavigationBar索引将用户路由到正确的屏幕

import 'package:flutter/material.dart';
import 'package:shared_preferences/shared_preferences.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter BottomNavigationBar',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _currentIndex = 0;
  final List<Widget> _screens = [
    Screen1(),
    Screen2(),
    Screen3(),
  ];

  @override
  void initState() {
    super.initState();
    _loadSavedIndex();
  }

  void _loadSavedIndex() async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    setState(() {
      _currentIndex = prefs.getInt('currentIndex') ?? 0;
    });
  }

  void _onItemTapped(int index) {
    setState(() {
      _currentIndex = index;
    });
    _saveCurrentIndex();
  }

  void _saveCurrentIndex() async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    await prefs.setInt('currentIndex', _currentIndex);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Flutter BottomNavigationBar'),
      ),
      body: IndexedStack(
        index: _currentIndex,
        children: _screens,
      ),
      bottomNavigationBar: BottomNavigationBar(
        currentIndex: _currentIndex,
        onTap: _onItemTapped,
        items: [
          BottomNavigationBarItem(
            icon: Icon(Icons.home),
            label: 'Screen 1',
          ),
          BottomNavigationBarItem(
            icon: Icon(Icons.business),
            label: 'Screen 2',
          ),
          BottomNavigationBarItem(
            icon: Icon(Icons.school),
            label: 'Screen 3',
          ),
        ],
      ),
    );
  }
}

class Screen1 extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Container(
      child: Center(
        child: Text('Screen 1'),
      ),
    );
  }
}

class Screen2 extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Container(
      child: Center(
        child: Text('Screen 2'),
      ),
    );
  }
}

class Screen3 extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Container(
      child: Center(
        child: Text('Screen 3'),
      ),
    );
  }
}