导航到新屏幕时保留底部导航栏

Question

我想在导航到新屏幕时保留底部导航栏 AppBar。返回页面时保存状态。

Answer 1

诀窍是在正文中使用“IndexedStack”，IndexedStack 工作者喜欢 Stack Widget：

IndexedStack(
  index: _selectedIndex,
  children: _widgetOptions,
)

传递“children”中的小部件列表和“index”中的小部件索引。

示例代码如下：

import 'package:flutter/material.dart';

Future<void> main() async {
  WidgetsFlutterBinding.ensureInitialized();
  runApp(
    MyApp(),
  );
}

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

class BottomNavPage extends StatefulWidget {
  const BottomNavPage({Key? key}) : super(key: key);

  @override
  _BottomNavPageState createState() => _BottomNavPageState();
}

class _BottomNavPageState extends State<BottomNavPage> {
  int _selectedIndex = 0;
  static const List<Widget> _widgetOptions = <Widget>[
    NavHome(),
    Text('Index 1: Business'),
    Text('Index 2: School'),
    Text('Index 3: Settings'),
  ];

  Widget navHome() {
    return Text(
      'Index 0: Home',
    );
  }

  void _onItemTapped(int index) {
    setState(() {
      _selectedIndex = index;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('BottomNavigationBar Sample')),
      body: IndexedStack(
        index: _selectedIndex,
        children: _widgetOptions,
      ),
      bottomNavigationBar: Material(
        child: BottomNavigationBar(
          items: const <BottomNavigationBarItem>[
            BottomNavigationBarItem(
              icon: Icon(Icons.home),
              label: 'Home',
              backgroundColor: Colors.blue,
            ),
            BottomNavigationBarItem(
              icon: Icon(Icons.business),
              label: 'Home',
              backgroundColor: Colors.blue,
            ),
            BottomNavigationBarItem(
              icon: Icon(Icons.school),
              label: 'Home',
              backgroundColor: Colors.blue,
            ),
            BottomNavigationBarItem(
              icon: Icon(Icons.settings),
              label: 'Home',
              backgroundColor: Colors.blue,
            ),
          ],
          currentIndex: _selectedIndex,
          selectedItemColor: Colors.orange[400],
          onTap: _onItemTapped,
        ),
      ),
    );
  }
}

class NavHome extends StatefulWidget {
  const NavHome({
    Key? key,
  }) : super(key: key);

  @override
  _NavHomeState createState() => _NavHomeState();
}

class _NavHomeState extends State<NavHome> {
  double _counter = 0;
  void incrementCounter() {
    setState(() {
      _counter++;
    });
  }

  void decrementCounter() {
    setState(() {
      _counter--;
    });
  }

  @override
  Widget build(BuildContext context) {
    // Return a widget number in the center of the screen and button to increment the number
    return Center(
      child: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: <Widget>[
          Text(
            'Counter',
          ),
          Text(
            '$_counter',
            style: Theme.of(context).textTheme.headline4,
          ),
          Row(
            mainAxisAlignment: MainAxisAlignment.center,
            children: [
              ElevatedButton(
                child: Text('Increment'),
                onPressed: incrementCounter,
              ),
              SizedBox(width: 10),
              ElevatedButton(
                child: Text('Decrement'),
                onPressed: decrementCounter,
              ),
            ],
          ),
        ],
      ),
    );
  }
}