unyo-dependency-injection

Unyo Dependency Injection with GetIt

Unyo uses GetIt as its service locator for dependency injection. All registrations happen in a single file (lib/core/di/locator.dart) and follow a clear two-phase initialization pattern.

The Service Locator

// lib/core/di/locator.dart
final sl = GetIt.instance;

sl is the global service locator instance used throughout the app. Every dependency — services, repositories, notifiers, cubits — is registered in and resolved from sl.

Two-Phase Initialization

Unyo initializes dependencies in two phases because some services depend on asynchronous platform APIs (like getApplicationSupportDirectory()) and others depend on Hive being ready.

Phase 1: setupLocator() — Called before runApp()

void setupLocator() async {
  // 1. Async platform dependencies first
  sl.registerSingletonAsync<Directory>(
    () => getApplicationSupportDirectory(),
    instanceName: config.applicationSupportDirectory,
  );
  await sl.isReady<Directory>(instanceName: config.applicationSupportDirectory);

  // 2. Singletons with no async dependencies
  sl.registerSingleton<Logger>(getLogger());
  sl.registerSingleton<AniyomiBridge>(AniyomiBridge());
  sl.registerSingleton<TorrentService>(TorrentService());
  sl.registerSingleton<SettingsService>(SettingsService());

  // 3. Lazy singletons (services, notifiers, repositories)
  sl.registerLazySingleton<HttpService>(() => HttpService());
  sl.registerLazySingleton<GraphQLService>(
    () => GraphQLService(httpService: sl<HttpService>(), endpoint: config.anilistGraphQLEndpoint),
    instanceName: config.anilistGraphQlService,
  );
  sl.registerLazySingleton<AppEffectHandler>(() => AppEffectHandler());

  // 4. Notifiers (all lazy singletons)
  sl.registerLazySingleton<AnimeNotifier>(() => AnimeNotifier());
  sl.registerLazySingleton<MangaNotifier>(() => MangaNotifier());
  // ... more notifiers

  // 5. Repositories (lazy singletons)
  sl.registerLazySingleton<AnimeRepositoryAnilist>(() => AnimeRepositoryAnilist());
  sl.registerLazySingleton<MangaRepositoryAnilist>(() => MangaRepositoryAnilist());

  // 6. Cubits (factories — new instance each time)
  sl.registerFactory<HomeCubit>(() => HomeCubit(
    sl<UserNotifier>(instanceName: config.loggedUserNotifier),
    sl<AnimeNotifier>(),
    sl<MangaNotifier>(),
    // ... all dependencies
  ));
}

Phase 2: setupLocatorAfterHiveInit() — Called after Hive initializes

void setupLocatorAfterHiveInit() {
  // Dependencies that require Hive to be ready
  sl.registerSingleton<ExtensionRepositoryAniyomi>(
    ExtensionRepositoryAniyomi(
      sl<UserRepositoryAnilist>(),
      sl<UserNotifier>(instanceName: config.loggedUserNotifier),
    ),
  );
}

Why two phases? ExtensionRepositoryAniyomi uses Hive boxes for storage, so it can't be constructed until after Hive is initialized. The main() function calls setupLocator() → Hive init → setupLocatorAfterHiveInit().

Registration Types

registerSingleton<T> — Eager, one instance forever

sl.registerSingleton<Logger>(getLogger());

• Created immediately at registration time
• Same instance returned for every sl<Logger>() call
• Use for: Logger, platform services, anything needed ASAP

registerLazySingleton<T> — Lazy, one instance forever (after first access)

sl.registerLazySingleton<AnimeRepositoryAnilist>(() => AnimeRepositoryAnilist());

• Created only when first accessed via sl<AnimeRepositoryAnilist>()
• Same instance for all subsequent calls
• Use for: Repositories, notifiers, services — things that are heavy or may not always be needed

registerFactory<T> — New instance every time

sl.registerFactory<HomeCubit>(() => HomeCubit(
  sl<UserNotifier>(instanceName: config.loggedUserNotifier),
  sl<AnimeNotifier>(),
));

• Factory function runs every time sl<HomeCubit>() is called
• Each call gets a fresh instance
• Use for: Cubits — each screen gets its own cubit instance

registerSingletonAsync<T> — Async eager singleton

sl.registerSingletonAsync<Directory>(
  () => getApplicationSupportDirectory(),
  instanceName: config.applicationSupportDirectory,
);
await sl.isReady<Directory>(instanceName: config.applicationSupportDirectory);

• Created asynchronously
• Must await isReady<T>() before using
• Use for: Platform dependencies that return Futures

Named Instances

When you need multiple registrations of the same type, use named instances:

// In config.dart
const String loggedUserNotifier = 'loggedUserNotifier';
const String newUserNotifier = 'newUserNotifier';

// Registration
sl.registerLazySingleton<UserNotifier>(() => UserNotifier(), instanceName: config.loggedUserNotifier);
sl.registerLazySingleton<UserNotifier>(() => UserNotifier(), instanceName: config.newUserNotifier);

// Resolution
sl<UserNotifier>(instanceName: config.loggedUserNotifier)  // Different instance
sl<UserNotifier>(instanceName: config.newUserNotifier)      // Different instance

Convention: Store instance name strings as const in lib/config/config.dart, not as magic strings in the locator.

Adding a New Dependency: Complete Workflow

Example: Adding a new StudioNotifier and StudioRepository

1. Create config constants (if adding named instances):

// lib/config/config.dart
const String studioNotifier = 'studioNotifier';

2. Register in setupLocator() in the correct section:

// Notifiers section
sl.registerLazySingleton<StudioNotifier>(() => StudioNotifier());

// Repositories section
sl.registerLazySingleton<StudioRepositoryAnilist>(() => StudioRepositoryAnilist());

// Cubits section (factories!)
sl.registerFactory<StudioCubit>(() => StudioCubit(
  sl<StudioNotifier>(),
  sl<StudioRepositoryAnilist>(),
));

3. If the dependency needs Hive, register in setupLocatorAfterHiveInit() instead.

4. Import the cubit/notifier in locator.dart:

import 'package:unyo/application/cubits/studio_cubit.dart';
import 'package:unyo/core/notification/studio_notifier.dart';

5. Use in screens via BlocProvider:

// In the screen widget
BlocProvider(
  create: (context) => sl<StudioCubit>(),
  child: const StudioListener(),
)

Registration Order Matters

GetIt resolves dependencies at construction time. If HomeCubit needs AnimeNotifier, then AnimeNotifier must be registered before HomeCubit. Within each phase, follow this order:

1. Platform dependencies (async singletons like Directory)
2. Core singletons (Logger, bridge services)
3. Services (HttpService, GraphQLService, TorrentService)
4. Singletons depending on services (ThemeService, SettingsService)
5. Notifiers (all lazy singletons)
6. Repositories (lazy singletons that depend on services)
7. Cubits (factories that depend on everything above)

Dependency Injection in Repositories

Repositories access services via the locator, not constructor injection:

class AnimeRepositoryAnilist with RepositoryMixin implements AnimeRepository {
  final GraphQLService _anilistGraphQLService = sl<GraphQLService>(
    instanceName: config.anilistGraphQlService,
  );
  final Logger _logger = sl<Logger>();

This is intentional — repositories are lazy singletons that only exist once, so direct locator access is simpler than threading services through constructors. Cubits, however, receive all their dependencies via constructor injection from the locator.

Common Pitfalls

• Registering after resolution: GetIt throws at runtime if you try to resolve a type that hasn't been registered. Always add new registrations to setupLocator() before any code that uses sl<T>().
• Missing await sl.isReady<T>(): For async singletons, you must wait for readiness before using them. The main() function handles this, but if you add a new async singleton, make sure to add the await.
• Using registerFactory for notifiers: Notifiers must be registerLazySingleton so all cubits share the same stream. Using registerFactory would create separate instances, breaking cross-cubit communication.
• Using registerSingleton for cubits: Cubits must be registerFactory to ensure each screen gets its own instance. Using registerSingleton would share state between screens and cause bugs.
• Missing named instance on resolution: If you register with instanceName, you must also resolve with the same instanceName:

  // WRONG — resolves the unnamed instance, not the logged user notifier
  sl<UserNotifier>()
  // CORRECT — resolves the named instance
  sl<UserNotifier>(instanceName: config.loggedUserNotifier)
  

• Circular dependencies: If A needs B and B needs A, GetIt can't resolve them. Break the cycle by using lazy resolution: pass a factory function instead of the actual instance.

Cross-references

• Notifier pattern details: See unyo-reactive-notifiers skill
• Cubit registration and wiring: See unyo-bloc-state-management skill
• Repository pattern details: See unyo-domain-data-layer skill