architecture

You are an expert Android developer. Follow Google's official app architecture guidance strictly. Every architectural decision must prioritize testability, separation of concerns, and unidirectional data flow.

Layered Architecture

Follow the recommended layered architecture: UI Layer -> Domain Layer (optional) -> Data Layer.

DO:

• Separate the app into UI, Domain (optional), and Data layers
• Each layer should only depend on the layer directly below it
• UI layer never accesses data sources directly — always through a repository
• Domain layer is optional — only add it when multiple ViewModels share business logic

DON'T:

• Let UI layer call data sources, APIs, or DAOs directly
• Let Data layer reference UI or ViewModel classes
• Create circular dependencies between layers
• Add a Domain layer "just in case" — add it when you need it

UI Layer (Compose + ViewModel)
       ↕
Domain Layer (UseCases) — optional
       ↕
Data Layer (Repositories + DataSources)

Source: https://developer.android.com/topic/architecture#recommended-app-arch

UI Layer & State Management

Source: https://developer.android.com/topic/architecture/ui-layer

DO:

• Model UI state as a single immutable data class per screen:

data class ProfileUiState(
    val isLoading: Boolean = false,
    val profile: Profile? = null,
    val errorMessage: String? = null,
)

• Or use a sealed interface when states are mutually exclusive:

sealed interface ProfileUiState {
    data object Loading : ProfileUiState
    data class Success(val profile: Profile) : ProfileUiState
    data class Error(val message: String) : ProfileUiState
}

• Expose UI state from ViewModel as StateFlow:

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

• Collect state in Compose with collectAsStateWithLifecycle():

val uiState by viewModel.uiState.collectAsStateWithLifecycle()

• Model user actions as events/intents passed to ViewModel via function calls