How to provide different instances of the same class in Dagger Hilt?

To provide different instances of the same class in Dagger Hilt, you can use qualifiers (@Named or custom ones).

1. Creating qualifiers:

   • Use @Named for simple cases, specifying a string name.
   • Create your own custom qualifier annotations for more complex scenarios or better semantics.

   // Example of a custom qualifier
   @Qualifier
   @Retention(AnnotationRetention.RUNTIME)
   annotation class ProductionApi
   
   @Qualifier
   @Retention(AnnotationRetention.RUNTIME)
   annotation class TestApi
   

2. Binding different instances using qualifiers:

   • In Hilt modules (@Module), inside classes with @Provides or @Binds, use qualifier annotations for methods returning instances.

   @Module
   @InstallIn(SingletonComponent::class) // Example scope
   object AppModule {
   
       @Provides
       @Singleton // Example scope
       @Named("개발") // @Named qualifier for the "Development" instance
       fun provideDevRepository(): Repository {
           return Repository("개발 환경") // Different instance or configuration
       }
   
       @Provides
       @Singleton // Example scope
       @Named("운영") // @Named qualifier for the "Production" instance
       fun provideProdRepository(): Repository {
           return Repository("운영 환경") // Different instance or configuration
       }
   
       // Using custom qualifiers
       @Provides
       @Singleton
       @ProductionApi
       fun provideProductionService(): MyService {
           return MyService("Production API endpoint")
       }
   
       @Provides
       @Singleton
       @TestApi
       fun provideTestService(): MyService {
           return MyService("Test API endpoint")
       }
   }
   

3. Injecting a specific instance:

   • In places where you need to inject a dependency (@AndroidEntryPoint), annotate the field or constructor parameter with the appropriate qualifier.

   @AndroidEntryPoint // For example, Fragment or Activity
   class MyFragment : Fragment() {
   
       @Inject
       @Named("개발") // Injecting the "Development" instance
       lateinit var devRepository: Repository
   
       @Inject
       @Named("운영") // Injecting the "Production" instance
       lateinit var prodRepository: Repository
   
       @Inject
       @ProductionApi // Injecting the production instance with a custom qualifier
       lateinit var productionService: MyService
   
       // ... usage of dependencies ...
   }