State Management

Overview

Provider + ChangeNotifier is used for state management. Each ViewModel is a ChangeNotifier subclass that extends BaseProvider.

ViewModel Registry

All ViewModels registered in service_locator.dart:

// service_locator.dart
Future<void> setupServiceLocator() async {
  // Auth
  getIt.registerFactory<AuthViewModel>(() => AuthViewModel(getIt<AuthService>()));

  // Core
  getIt.registerFactory<HomeViewModel>(() => HomeViewModel(getIt<StudentService>()));

  // Features
  getIt.registerFactory<AttendanceViewModel>(() => AttendanceViewModel(getIt<AttendanceService>()));
  getIt.registerFactory<ExamViewModel>(() => ExamViewModel(getIt<ExamService>()));
  getIt.registerFactory<FeeViewModel>(() => FeeViewModel(getIt<FeeService>()));
  getIt.registerFactory<AnnouncementViewModel>(() => AnnouncementViewModel(getIt<AnnouncementService>()));
  getIt.registerFactory<TimetableViewModel>(() => TimetableViewModel(getIt<TimetableService>()));
  getIt.registerFactory<LeaveViewModel>(() => LeaveViewModel(getIt<LeaveService>()));
  getIt.registerFactory<EventViewModel>(() => EventViewModel(getIt<EventService>()));
  getIt.registerFactory<TeacherViewModel>(() => TeacherViewModel(getIt<TeacherService>()));
  getIt.registerFactory<MessageViewModel>(() => MessageViewModel(getIt<MessageService>()));
  getIt.registerFactory<NotificationViewModel>(() => NotificationViewModel(getIt<NotificationService>()));
}

Using ViewModels in Screens

// In MultiProvider at app root:
MultiProvider(
  providers: [
    ChangeNotifierProvider(create: (_) => getIt<AuthViewModel>()),
    ChangeNotifierProvider(create: (_) => getIt<HomeViewModel>()),
    ChangeNotifierProvider(create: (_) => getIt<AttendanceViewModel>()),
    // ...
  ],
  child: MaterialApp(...),
)

// In a screen:
class AttendanceScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Consumer<AttendanceViewModel>(
      builder: (context, vm, _) {
        if (vm.isLoading) return const CircularProgressIndicator();
        if (vm.hasError) return Text(vm.errorMessage!);
        return ListView.builder(
          items: vm.records,
          itemBuilder: (_, record) => AttendanceTile(record: record),
        );
      },
    );
  }
}

BaseProvider Request Handler

The requestHandler wrapper in BaseProvider handles loading/error state automatically:

class AttendanceViewModel extends BaseProvider {
  Future<void> loadAttendance() async {
    await requestHandler(() async {
      _records = await _service.getAttendance(_selectedStudentId);
    });
    notifyListeners();  // Call after requestHandler since it doesn't notify
  }
}

Loading Overlay

A common pattern is to show a loading overlay during navigation or data fetches:

if (vm.isLoading) {
  return const Scaffold(
    body: Center(child: CircularProgressIndicator()),
  );
}

Student Context

The HomeViewModel holds the currently selected studentId which is passed to all other ViewModels:

class HomeViewModel extends BaseProvider {
  String? _currentStudentId;
  List<Student> _students = [];

  String? get currentStudentId => _currentStudentId;
  List<Student> get students => _students;

  void switchStudent(String studentId) {
    _currentStudentId = studentId;
    _loadStudentData();
    notifyListeners();
  }
}