avra-cadavra/dependency-injection-getit

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

// Use registerLazySingleton (NOT registerSingleton)
sl.registerLazySingleton<MyService>(() => MyService(
  dependencyService: sl<DependencyService>(),
));

With Dependencies

// Register dependencies BEFORE dependents
sl.registerLazySingleton(() => DependencyService());
sl.registerLazySingleton(() => MyService(
  dependencyService: sl<DependencyService>(),
));

Check Before Registration

// Check if already registered to avoid duplicates
if (!sl.isRegistered<MyService>()) {
  sl.registerLazySingleton<MyService>(() => MyService(
    dependencyService: sl<DependencyService>(),
  ));
}

With Documentation Comment

// Register MyService (for specific purpose description)
sl.registerLazySingleton<MyService>(() => MyService(
  dependencyService: sl<DependencyService>(),
));

Service Constructor Pattern

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:

sl.registerLazySingleton(() => ServiceA(serviceB: sl<ServiceB>()));
sl.registerLazySingleton(() => ServiceB(serviceA: sl<ServiceA>())); // ERROR

❌ Wrong Order:

sl.registerLazySingleton(() => MyService(dep: sl<Dependency>())); // ERROR: Dependency not registered yet
sl.registerLazySingleton(() => Dependency());

❌ Wrong Lifecycle:

sl.registerFactory(() => MyService()); // BAD: Should be singleton

Reference

See existing registrations in:

• lib/injection_container_core.dart
• lib/injection_container.dart