【Flutter】BottomNavigationBarの実装方法

環境

• OS : Windows11
• Edit : VS Code
• Flutter : 3.0.5

画面を準備

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Home'),
      ),
      body: const Center(
          child: Text('Home', style: TextStyle(fontSize: 32.0))),
    );
  }
}

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Business'),
      ),
      body: const Center(
          child: Text('Business', style: TextStyle(fontSize: 32.0))),
    );
  }
}

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Settings'),
      ),
      body: const Center(
          child: Text('Settingss', style: TextStyle(fontSize: 32.0))),
    );
  }
}

デフォルトな見た目での実装

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

  @override
  State<MyStatefulWidget> createState() => _MyStatefulWidgetState();
}

class _MyStatefulWidgetState extends State<MyStatefulWidget> {
  int _selectedIndex = 0;
  static const List<Widget> _widgetOptions = <Widget>[
    HomeScreen(),
    BusinessScreen(),
    SettingsScreen(),
  ];

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: _widgetOptions.elementAt(_selectedIndex),
      ),
      bottomNavigationBar: BottomNavigationBar(
        items: const <BottomNavigationBarItem>[
          BottomNavigationBarItem(
            icon: Icon(Icons.home),
            label: 'Home',
          ),
          BottomNavigationBarItem(
            icon: Icon(Icons.business),
            label: 'Business',
          ),
          BottomNavigationBarItem(
            icon: Icon(Icons.settings),
            label: 'Settings',
          )
        ],
        currentIndex: _selectedIndex,
        selectedItemColor: Colors.amber[800],
        onTap: _onItemTapped,
        type: BottomNavigationBarType.fixed,
      ),
    );
  }
}

背景色を変更する

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

  @override
  State<MyStatefulWidget> createState() => _MyStatefulWidgetState();
}

class _MyStatefulWidgetState extends State<MyStatefulWidget> {
  int _selectedIndex = 0;
  static const List<Widget> _widgetOptions = <Widget>[
    HomeScreen(),
    BusinessScreen(),
    SettingsScreen(),
  ];

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: _widgetOptions.elementAt(_selectedIndex),
      ),
      bottomNavigationBar: BottomNavigationBar(
        items: const <BottomNavigationBarItem>[
          BottomNavigationBarItem(
            icon: Icon(Icons.home),
            label: 'Home',
            backgroundColor: Colors.red, //追加
          ),
          BottomNavigationBarItem(
            icon: Icon(Icons.business),
            label: 'Business',
            backgroundColor: Colors.green, //追加
          ),
          BottomNavigationBarItem(
            icon: Icon(Icons.settings),
            label: 'Settings',
            backgroundColor: Colors.purple, //追加
          )
        ],
        currentIndex: _selectedIndex,
        selectedItemColor: Colors.amber[800],
        onTap: _onItemTapped,
        type: BottomNavigationBarType.shifting, //shiftingに変更
      ),
    );
  }
}