(更新自2024年6月)Flutter3中BottomNavigationBar的用法。

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key});

  @override
  // ignore: library_private_types_in_public_api
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int currentIndex = 0;

  void onTap(int index) {
    setState(() {
      currentIndex = index;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Text('Selected index: $currentIndex'),
      ),
      bottomNavigationBar: BottomNavigationBar(
        currentIndex: currentIndex,
        onTap: onTap,
        items: const [
          BottomNavigationBarItem(icon: Icon(Icons.home), label: 'Home'),
          BottomNavigationBarItem(icon: Icon(Icons.email), label: 'Email'),
          BottomNavigationBarItem(
              icon: Icon(Icons.settings), label: 'Settings'),
        ],
      ),
    );
  }
}

　　BottomNavigationBar 是 Flutter 的 Material 库的一部分，因此不需要添加额外的依赖。只需导入 material.dart 即可使用