dependency-injection

You are an expert in Hilt dependency injection for Android. Use Hilt as the standard DI framework. Follow constructor injection by default, use proper scoping, and keep modules clean and focused.

Setup

DO:

• Annotate the Application class with @HiltAndroidApp:

@HiltAndroidApp
class MyApp : Application()

• Annotate Activities with @AndroidEntryPoint:

@AndroidEntryPoint
class MainActivity : ComponentActivity()

• Annotate ViewModels with @HiltViewModel:

@HiltViewModel
class ProfileViewModel @Inject constructor(
    private val getProfileUseCase: GetProfileUseCase,
) : ViewModel()

DON'T:

• Forget @HiltAndroidApp on Application — Hilt won't work without it
• Create ViewModel instances with ViewModelProvider manually — use hiltViewModel() in Compose
• Use Koin or manual DI in new projects — use Hilt for standardized, compile-time safe DI

Constructor Injection (Preferred)

Source: https://developer.android.com/training/dependency-injection/hilt-android#inject-interfaces

DO:

• Use constructor injection as the default approach:

class UserRepository @Inject constructor(
    private val remoteDataSource: UserRemoteDataSource,
    private val localDataSource: UserLocalDataSource,
) {
    // ...
}

• All dependencies should be injectable — avoid object singletons that hold state

DON'T:

• Use field injection except in Android framework classes (Activity, Fragment, Service)
• Create instances with new / direct constructor calls for injectable classes

Modules & Bindings

DO:

• Use @Binds for binding an interface to its implementation (preferred over @Provides):

@Module
@InstallIn(SingletonComponent::class)
abstract class RepositoryModule {
    @Binds
    abstract fun bindUserRepository(impl: UserRepositoryImpl): UserRepository
}

• Use @Provides for third-party classes and builder patterns:

@Module
@InstallIn(SingletonComponent::class)
object NetworkModule {
    @Provides
    @Singleton
    fun provideOkHttpClient(): OkHttpClient =
        OkHttpClient.Builder()
            .addInterceptor(AuthInterceptor())
            .build()

    @Provides
    @Singleton
    fun provideRetrofit(client: OkHttpClient): Retrofit =
        Retrofit.Builder()
            .baseUrl(BuildConfig.BASE_URL)
            .client(client)
            .addConverterFactory(Json.asConverterFactory("application/json".toMediaType()))
            .build()
}

• Use @Qualifier for multiple bindings of the same type:

@Qualifier
@Retention(AnnotationRetention.BINARY)
annotation class IoDispatcher

@Module
@InstallIn(SingletonComponent::class)
object DispatcherModule {
    @Provides
    @IoDispatcher
    fun provideIoDispatcher(): CoroutineDispatcher = Dispatchers.IO
}

• Organize modules by concern: NetworkModule, DatabaseModule, RepositoryModule