Android Data Layer

Android Data Layer & Offline-First

Instructions

The Data Layer coordinates data from multiple sources.

1. Repository Pattern

• Role: Single Source of Truth (SSOT).
• Logic: The repository decides whether to return cached data or fetch fresh data.
• Implementation: ```kotlin class NewsRepository @Inject constructor( private val newsDao: NewsDao, private val newsApi: NewsApi ) { // Expose data from Local DB as the source of truth val newsStream: Flow<List<News>> = newsDao.getAllNews()

// Sync operation suspend fun refreshNews() { val remoteNews = newsApi.fetchLatest() newsDao.insertAll(remoteNews) } }

### 2. Local Persistence (Room)
*   **Usage**: Primary cache and offline storage.
*   **Entities**: Define `@Entity` data classes.
*   **DAOs**: Return `Flow<T>` for observable data.

### 3. Remote Data (Retrofit)
*   **Usage**: Fetching data from backend.
*   **Response**: Use `suspend` functions in interfaces.
*   **Error Handling**: Wrap network calls in `try-catch` blocks or a `Result` wrapper to handle exceptions (NoInternet, 404, etc.) gracefully.

### 4. Synchronization
*   **Read**: "Stale-While-Revalidate". Show local data immediately, trigger a background refresh.
*   **Write**: "Outbox Pattern" (Advanced). Save local change immediately, mark as "unsynced", use `WorkManager` to push changes to server.

### 5. Dependency Injection
*   Bind Repository interfaces to implementations in a Hilt Module.

@Binds abstract fun bindNewsRepository(impl: OfflineFirstNewsRepository): NewsRepository