Android Dependency Injection with Hilt¶

Hilt (built on Dagger) as the recommended DI framework for Android. Parallels Spring's IoC container but with Android lifecycle awareness.

Key Facts¶

• Hilt is Google's recommended DI for Android - built on Dagger 2 with less boilerplate
• @HiltAndroidApp on Application class enables Hilt
• @AndroidEntryPoint on Activity/Fragment enables injection
• @HiltViewModel with @Inject constructor for ViewModel injection
• @Module + @InstallIn for providing third-party dependencies
• @Singleton, @ActivityScoped, @ViewModelScoped control lifecycle
• Parallels Spring's @Component/@Service/@Bean pattern

Patterns¶

Application Setup¶

@HiltAndroidApp
class MyApp : Application()

Activity/Fragment Injection¶

@AndroidEntryPoint
class MainActivity : AppCompatActivity() {
    @Inject lateinit var repository: UserRepository
}

ViewModel Injection¶

@HiltViewModel
class UserViewModel @Inject constructor(
    private val repository: UserRepository
) : ViewModel() {
    // No ViewModelFactory needed!
}

Module for Third-Party Dependencies¶

@Module
@InstallIn(SingletonComponent::class)
object AppModule {
    @Provides @Singleton
    fun provideApiService(): ApiService {
        return Retrofit.Builder()
            .baseUrl(BASE_URL)
            .addConverterFactory(GsonConverterFactory.create())
            .build()
            .create(ApiService::class.java)
    }

    @Provides @Singleton
    fun provideUserRepository(api: ApiService, dao: UserDao): UserRepository {
        return UserRepository(api, dao)
    }

    @Provides @Singleton
    fun provideDatabase(@ApplicationContext context: Context): AppDatabase {
        return Room.databaseBuilder(context, AppDatabase::class.java, "app_db").build()
    }

    @Provides
    fun provideUserDao(db: AppDatabase): UserDao = db.userDao()
}

Spring IoC vs Hilt Comparison¶

Gotchas¶

• @Inject lateinit var fields must NOT be private in Activities/Fragments
• @HiltViewModel requires @Inject constructor - cannot use no-arg constructor
• Hilt modules must specify @InstallIn with appropriate component (SingletonComponent, ActivityComponent, etc.)
• Missing @AndroidEntryPoint on Fragment's host Activity causes runtime crash

See Also¶

• spring ioc beans - Spring's equivalent IoC container
• android architecture mvvm - ViewModel injection patterns
• kotlin coroutines - Coroutines in injected services