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android-data-layer

Guidance on implementing the Data Layer using Repository pattern, Room (Local), and Retrofit (Remote) with offline-first synchronization.

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Coding & debugging
License
Apache-2.0
Last commit
Jul 28, 2026

.github/skills/architecture/android-data-layer/SKILL.md

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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: 
    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

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