The operator '[]' isn't defined for the type 'List'. Try defining the operator '[]'

I face this problem when I want to add lists.dart in BottomNavigationBarItem. in bottom of scaffold it shows red underline- body: _children[_currentIndex],

but don't know, what is the actual problem. what does it mean by

The operator '[]' isn't defined for the type 'List'

?

this is the full code of main.dart

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

class Main extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.deepPurple,
      ),
      home: MainPage(),
    );
  }
}

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

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

class _MainPageState extends State<MainPage> {
  late SharedPreferences sharedPreferences;
  int _currentIndex = 0;
  final List _children = [
    Home(),
    OrganizationData(),
    Notifications(),
    More(),
  ] as List;

  void onTapped(int index) {
    setState(() {
      _currentIndex = index;
    });
  }

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

  checkLoginStatus() async {
    sharedPreferences = await SharedPreferences.getInstance();
    if (sharedPreferences.getString("token") == null) {
      Navigator.of(context).pushAndRemoveUntil(
          MaterialPageRoute(builder: (BuildContext context) => LoginPage()),
          (Route<dynamic> route) => false);
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        leadingWidth: 80,
        toolbarHeight: 80,
        titleSpacing: -15.0,
        title: ListTile(
          title: Text(
            "FAYZULLAH",
            style: TextStyle(
              fontWeight: FontWeight.bold,
              fontSize: 14,
            ),
          ),
          subtitle: Text(
            "Jr. executive",
            style: TextStyle(
              fontSize: 12,
            ),
          ),
        ),
        leading: GestureDetector(
          onTap: () {},
          child: Container(
            padding: EdgeInsets.all(10.0),
            margin: EdgeInsets.all(10.0),
            decoration: new BoxDecoration(
              borderRadius: BorderRadius.all(
                Radius.circular(50.0),
              ),
              border: Border.all(
                width: 1,
                style: BorderStyle.solid,
                color: Colors.black12,
              ),
              image: DecorationImage(
                image: AssetImage('assets/fozuda.png'),
              ),
            ),
          ),
        ),
        actions: [
          IconButton(
            icon: Icon(
              Icons.logout_rounded,
              size: 20,
            ),
            color: Colors.black,
            onPressed: () {
              sharedPreferences.clear();
              sharedPreferences.commit();
              Navigator.of(context).pushAndRemoveUntil(
                  MaterialPageRoute(
                      builder: (BuildContext context) => LoginPage()),
                  (Route<dynamic> route) => false);
            },
          ),
        ],
        backgroundColor: Colors.yellow,
      ),
      bottomNavigationBar: BottomNavigationBar(
        onTap: onTapped,
        currentIndex: _currentIndex,
        type: BottomNavigationBarType.fixed,
        // backgroundColor: Colors.yellow,
        items: const <BottomNavigationBarItem>[
          BottomNavigationBarItem(
            icon: Icon(Icons.home),
            label: 'Home',
          ),
          BottomNavigationBarItem(
            icon: Icon(Icons.list),
            label: 'Lists',
          ),
          BottomNavigationBarItem(
            icon: Icon(Icons.notifications),
            label: 'Notification',
          ),
          BottomNavigationBarItem(
            icon: Icon(Icons.more_horiz_rounded),
            label: 'More',
          ),
        ],
      ),
      body: _children[_currentIndex],
    );
  }
}

and this is the lists.dart code

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

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

class _OrganizationDataState extends State<OrganizationData> {
  late Future<List> futureAlbum;

  @override
  void initState() {
    super.initState();
    futureAlbum = listData();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: FutureBuilder<List>(
          future: futureAlbum,
          builder: (context, snapshot) {
            if (snapshot.hasData) {
              // print(snapshot.data);
              return Text(snapshot.data!.fullName);
            } else if (snapshot.hasError) {
              return Text('${snapshot.error}');
            }
            return const CircularProgressIndicator();
          },
        ),
      ),
    );
  }
}


Future<List> listData() async {

  Dio dio = new Dio();
  dio.options.headers['Content-Type'] = 'application/json';
  final body = {'limit': 1, 'orderBy': 'idEmployee', 'orderType': 'DESC'};
  final response = await dio.post(url, data: body);
  if (response.statusCode == 200) {
    return List.fromJson(response.data["data"]["data"][0]);
  } else {
    throw Exception('Failed!');
  }
}

class List {
  final int idEmployee;
  final String fullName;

  List({
    required this.idEmployee,
    required this.fullName,
  });

  factory List.fromJson(Map<String, dynamic> json) {
    return List(
      idEmployee: json['idEmployee'],
      fullName: json['fullName'],
    );
  }
}

This is run console

Rename your List class in lists.dart in some other name and correct the name everywhere you used your List class.

Because there is a built in object named List So, you cannot name your classes "List".

Naming your own classes "List" will override the built in List class. That's why dart tells that "The operator '[]' isn't defined for the type 'List'".

So, change your class name everywhere you used the class.