[G1-Sync] Manual knowledge update

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
+```kotlin
+@HiltAndroidApp
+class App : Application()
+
+// AndroidManifest.xml — name=".App"
+```
+
+### Module — 외부 라이브러리 binding
+```kotlin
+@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
+```kotlin
+@Singleton
+class UserRepo @Inject constructor(
+    private val api: UserApi,
+    private val dao: UserDao,
+) { ... }
+```
+
+### ViewModel 주입
+```kotlin
+@HiltViewModel
+class ProfileViewModel @Inject constructor(
+    private val repo: UserRepo,
+    private val savedState: SavedStateHandle,
+) : ViewModel() { ... }
+```
+
+### Compose
+```kotlin
+@Composable
+fun ProfileScreen(viewModel: ProfileViewModel = hiltViewModel()) { ... }
+```
+
+### Worker 주입
+```kotlin
+@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
+```kotlin
+@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]]