Android Compose

When to activate

• Building Android apps with Jetpack Compose
• Implementing MVVM architecture with ViewModel and StateFlow
• Setting up Room database for local persistence
• Configuring Hilt for dependency injection
• Implementing Material 3 design system

When NOT to use

• For cross-platform apps (use react-native-expo or flutter-widgets)
• For iOS-only development
• For legacy XML-based Android UI

Instructions

1. Project structure. Feature modules: :feature:auth, :feature:feed, :core:data, :core:domain, :core:ui.
2. Jetpack Compose UI. Stateless composables with state hoisting. Use remember for local, ViewModel for screen-level, DataStore for persistent.
3. ViewModel + StateFlow. Expose StateFlow<UiState> from ViewModel. Use sealed class UiState for loading/success/error states.
4. Room database. @Entity for tables, @Dao for queries, @Database for setup. Use Flow return types for reactive queries.
5. Hilt DI. @HiltAndroidApp on Application, @AndroidEntryPoint on Activities, @Inject for constructor injection.
6. Navigation. Navigation Compose with type-safe routes. NavHost with composable destinations. Deep link support via navDeepLink.
7. Performance. LazyColumn/LazyRow for lists, derivedStateOf to avoid recomputation, key for stable identities in lists.

Example

@HiltViewModel
class FeedViewModel @Inject constructor(
    private val repository: FeedRepository
) : ViewModel() {

    private val _uiState = MutableStateFlow<FeedUiState>(FeedUiState.Loading)
    val uiState: StateFlow<FeedUiState> = _uiState.asStateFlow()

    fun loadFeed() {
        viewModelScope.launch {
            repository.getFeed()
                .catch { _uiState.value = FeedUiState.Error(it.message) }
                .collect { posts -> _uiState.value = FeedUiState.Success(posts) }
        }
    }
}

sealed class FeedUiState {
    object Loading : FeedUiState()
    data class Success(val posts: List<Post>) : FeedUiState()
    data class Error(val message: String?) : FeedUiState()
}