--- name: dependency-injection-getit description: Guides GetIt dependency injection patterns for service registration. Use when creating new services, registering dependencies, or refactoring service architecture. --- # Dependency Injection with GetIt ## Core Pattern All services must be registered in dependency injection containers using GetIt. ## Registration Locations - **Core Services:** `lib\/injection_container_core.dart` - **Domain Services:** `lib\/injection_container.dart` - **AI Services:** `lib\/injection_container_ai.dart` - **Payment Services:** `lib\/injection_container_payment.dart` - **Admin Services:** `lib\/injection_container_admin.dart` - **Other Modules:** Separate containers as needed ## Registration Pattern ### Basic Registration ```dart \/\/ Use registerLazySingleton (NOT registerSingleton) sl.registerLazySingleton(() => MyService( dependencyService: sl(), )); ``` ### With Dependencies ```dart \/\/ Register dependencies BEFORE dependents sl.registerLazySingleton(() => DependencyService()); sl.registerLazySingleton(() => MyService( dependencyService: sl(), )); ``` ### Check Before Registration ```dart \/\/ Check if already registered to avoid duplicates if (!sl.isRegistered()) { sl.registerLazySingleton(() => MyService( dependencyService: sl(), )); } ``` ### With Documentation Comment ```dart \/\/ Register MyService (for specific purpose description) sl.registerLazySingleton(() => MyService( dependencyService: sl(), )); ``` ## Service Constructor Pattern ```dart class MyService { final DependencyService _dependencyService; final OptionalService? _optionalService; MyService({ required DependencyService dependencyService, OptionalService? optionalService, }) : _dependencyService = dependencyService, _optionalService = optionalService; } ``` ## Dependency Order Rules 1. **Core services first** - Register foundational services (StorageService, Logger, Database) before others 2. **Dependencies before dependents** - Always register dependencies before services that depend on them 3. **Module separation** - Register core services, then domain services, then feature services ## Common Pitfalls **❌ Circular Dependency:** ```dart sl.registerLazySingleton(() => ServiceA(serviceB: sl())); sl.registerLazySingleton(() => ServiceB(serviceA: sl())); \/\/ ERROR ``` **❌ Wrong Order:** ```dart sl.registerLazySingleton(() => MyService(dep: sl())); \/\/ ERROR: Dependency not registered yet sl.registerLazySingleton(() => Dependency()); ``` **❌ Wrong Lifecycle:** ```dart sl.registerFactory(() => MyService()); \/\/ BAD: Should be singleton ``` ## Reference See existing registrations in: - `lib\/injection_container_core.dart` - `lib\/injection_container.dart`