Android Modern Architecture & Modularization

Instructions

When designing or refactoring an Android application, adhere to the Guide to App Architecture and Clean Architecture principles.

1. High-Level Layers

Structure the application into three primary layers. Dependencies must strictly flow inwards (or downwards) to the core logic.

• UI Layer (Presentation):

• Responsibility: Displaying data and handling user interactions.

• Components: Activities, Fragments, Composables, ViewModels.

• Dependencies: Depends on the Domain Layer (or Data Layer if simple). Never depends on the Data Layer implementation details directly.

• Domain Layer (Business Logic) [Optional but Recommended]:

• Responsibility: Encapsulating complex business rules and reuse.

• Components: Use Cases (e.g., GetLatestNewsUseCase ), Domain Models (pure Kotlin data classes).

• Pure Kotlin: Must NOT contain any Android framework dependencies (no android.* imports).

• Dependencies: Depends on Repository Interfaces.

• Data Layer:

• Responsibility: Managing application data (fetching, caching, saving).

• Components: Repositories (implementations), Data Sources (Retrofit APIs, Room DAOs).

• Dependencies: Depends only on external sources and libraries.

2. Dependency Injection with Hilt

Use Hilt for all dependency injection.

• @HiltAndroidApp: Annotate the Application class.

• @AndroidEntryPoint: Annotate Activities and Fragments.

• @HiltViewModel: Annotate ViewModels; use standard constructor injection.

• Modules:

• Use @Module and @InstallIn(SingletonComponent::class) for app-wide singletons (e.g., Network, Database).

• Use @Binds in an abstract class to bind interface implementations (cleaner than @Provides ).

3. Modularization Strategy

For production apps, use a multi-module strategy to improve build times and separation of concerns.

• :app: The main entry point, connects features.

• :core:model: Shared domain models (Pure Kotlin).

• :core:data: Repositories, Data Sources, Database, Network.

• :core:domain: Use Cases and Repository Interfaces.

• :core:ui: Shared Composables, Theme, Resources.

• :feature:[name]: Standalone feature modules containing their own UI and ViewModels. Depends on :core:domain and :core:ui .

4. Checklist for implementation

• Ensure Domain layer has no Android dependencies.

• Repositories should default to main-safe suspend functions (use Dispatchers.IO internally if needed).

• ViewModels should interact with the UI layer via StateFlow (see android-viewmodel skill).