2nd/10_Wiki/Topics/Coding/Android_Hilt_DI_Patterns.md

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id: android-hilt-di-patterns title: Android Hilt — DI 모듈과 스코프 category: Coding status: draft source_trust_level: B verification_status: conceptual created_at: 2026-05-09 updated_at: 2026-05-09 tags: [android, hilt, di, dagger, vibe-coding] tech_stack: { language: "Kotlin / Hilt", applicable_to: ["Android"] } applied_in: [] aliases: [@HiltAndroidApp, @Module, @Provides, ViewModelComponent]

Android Hilt — DI

Dagger 의 Android 친화 wrapper. 컴포넌트 = 스코프. ApplicationComponent (Singleton), ActivityComponent, FragmentComponent, ViewModelComponent. 잘못된 스코프 = leak 또는 잘못된 인스턴스 공유.

📖 핵심 개념

• @HiltAndroidApp: Application 클래스에. 부팅.
• @AndroidEntryPoint: Activity / Fragment / View / Service 에.
• @HiltViewModel: ViewModel 자동 주입.
• @Module + @InstallIn: 어떤 컴포넌트에 binding.

💻 코드 패턴

부팅

@HiltAndroidApp
class App : Application()

// AndroidManifest.xml — name=".App"

Module — 외부 라이브러리 binding

@Module
@InstallIn(SingletonComponent::class)
object NetworkModule {

    @Provides @Singleton
    fun retrofit(): Retrofit = Retrofit.Builder()
        .baseUrl("https://api.example.com/")
        .addConverterFactory(MoshiConverterFactory.create())
        .build()

    @Provides @Singleton
    fun userApi(retrofit: Retrofit): UserApi = retrofit.create(UserApi::class.java)
}

@Module
@InstallIn(SingletonComponent::class)
abstract class RepoModule {
    @Binds @Singleton
    abstract fun bindUserRepo(impl: UserRepoImpl): UserRepo
}

Scoped repository

@Singleton
class UserRepo @Inject constructor(
    private val api: UserApi,
    private val dao: UserDao,
) { ... }

ViewModel 주입

@HiltViewModel
class ProfileViewModel @Inject constructor(
    private val repo: UserRepo,
    private val savedState: SavedStateHandle,
) : ViewModel() { ... }

Compose

@Composable
fun ProfileScreen(viewModel: ProfileViewModel = hiltViewModel()) { ... }

Worker 주입

@HiltWorker
class SyncWorker @AssistedInject constructor(
    @Assisted ctx: Context,
    @Assisted params: WorkerParameters,
    private val repo: SyncRepo,
) : CoroutineWorker(ctx, params) { ... }

// App 에서
@HiltAndroidApp
class App : Application(), Configuration.Provider {
    @Inject lateinit var workerFactory: HiltWorkerFactory
    override val workManagerConfiguration: Configuration
        get() = Configuration.Builder().setWorkerFactory(workerFactory).build()
}

Qualifier — 같은 타입 다른 인스턴스

@Qualifier annotation class Authed
@Qualifier annotation class Public

@Provides @Singleton @Authed
fun authedClient(): OkHttpClient = OkHttpClient.Builder().addInterceptor(AuthInterceptor()).build()

@Provides @Singleton @Public
fun publicClient(): OkHttpClient = OkHttpClient()

class Repo @Inject constructor(@Authed private val client: OkHttpClient) { ... }

🤔 의사결정 기준

인스턴스 lifecycle	스코프
앱 전체 (DB, network client, repo)	@Singleton in SingletonComponent
Activity 동안 (navigation graph)	@ActivityRetainedScoped
ViewModel 동안	@ViewModelScoped
Fragment 동안	@FragmentScoped
매번 새로	scope 없음 (default)

❌ 안티패턴

• 모든 곳 @Singleton: 큰 객체 메모리 영구 점유. 필요한 곳만.
• Activity scope 인데 ViewModel 에 주입: ViewModel 이 Activity 보다 오래 → leak.
• Context 잘못된 종류: ApplicationContext vs ActivityContext. 가장 작은 scope.
• 모듈을 잘못된 컴포넌트에 InstallIn: 의존성 못 찾음.
• @Provides 와 @Binds 혼용 + 같은 타입: ambiguous.
• 테스트 환경에서 production module 그대로: 외부 의존. @TestInstallIn 으로 fake.
• ViewModel constructor 에 Context 주입: leak. @ApplicationContext 만.

🤖 LLM 활용 힌트

• 신규 Android = Hilt 디폴트.
• Singleton vs ViewModelScoped 명확히.
• Test 는 hiltRules + fake module.

🔗 관련 문서

• Android_Room_Patterns
• Android_WorkManager_Patterns