android-clean-architecture

# Android Clean Architecture Clean Architecture patterns for Android and KMP projects. Covers module boundaries, dependency inversion, UseCase/Repository patterns, and data layer design with Room, SQLDelight, and Ktor. ## When to Activate - Structuring Android or KMP project modules - Implementing UseCases, Repositories, or DataSources - Designing data flow between layers (domain, data, presentation) - Setting up dependency injection with Koin or Hilt - Working with Room, SQLDelight, or Ktor in a layered architecture ## Module Structure ### Recommended Layout ``` project/ ├── app/ # Android entry point, DI wiring, Application class ├── core/ # Shared utilities, base classes, error types ├── domain/ # UseCases, domain models, repository interfaces (pure Kotlin) ├── data/ # Repository implementations, DataSources, DB, network ├── presentation/ # Screens, ViewModels, UI models, navigation ├── design-system/ # Reusable Compose components, theme, typography └── feature/ # Feature modules (optional, for larger projects) ├── auth/ ├── settings/ └── profile/ ``` ### Dependency Rules ``` app → presentation, domain, data, core presentation → domain, design-system, core data → domain, core domain → core (or no dependencies) core → (nothing) ``` **Critical**: `domain` must NEVER depend on `data`, `presentation`, or any framework. It contains pure Kotlin only. ## Domain Layer ### UseCase Pattern Each UseCase represents one business operation. Use `operator fun invoke` for clean call sites: ```kotlin class GetItemsByCategoryUseCase( private val repository: ItemRepository ) { suspend operator fun invoke(category: String): Result> { return repository.getItemsByCategory(category) } } // Flow-based UseCase for reactive streams class ObserveUserProgressUseCase( private val repository: UserRepository ) { operator fun invoke(userId: String): Flow { return repository.observeProgress(userId) } } ``` ### Domain Models Domain models are plain Kotlin data classes — no framework annotations: ```kotlin data class Item( val id: String, val title: String, val description: String, val tags: List, val status: Status, val category: String ) enum class Status { DRAFT, ACTIVE, ARCHIVED } ``` ### Repository Interfaces Defined in domain, implemented in data: ```kotlin interface ItemRepository { suspend fun getItemsByCategory(category: String): Result> suspend fun saveItem(item: Item): Result fun observeItems(): Flow> } ``` ## Data Layer ### Repository Implementation Coordinates between local and remote data sources: ```kotlin class ItemRepositoryImpl( private val localDataSource: ItemLocalDataSource, private val remoteDataSource: ItemRemoteDataSource ) : ItemRepository { override suspend fun getItemsByCategory