android-development

name android-development description Create production-quality Android applications following Google's official architecture guidance and NowInAndroid best practices. Use when building Android apps with Kotlin, Jetpack Compose, MVVM architecture, Hilt dependency injection, Room database, or multi-module projects. Triggers on requests to create Android projects, screens, ViewModels, repositories, feature modules, or when asked about Android architecture patterns. Android Development Build Android applications following Google's official architecture guidance, as demonstrated in the NowInAndroid reference app. Quick Reference Task Reference File Project structure & modules modularization.md Architecture layers (UI, Domain, Data) architecture.md Jetpack Compose patterns compose-patterns.md Gradle & build configuration gradle-setup.md Testing approach testing.md Workflow Decision Tree Creating a new project? → Read modularization.md for project structure → Use templates in assets/templates/ Adding a new feature? → Create feature module with api and impl submodules → Follow patterns in architecture.md Building UI screens? → Read compose-patterns.md → Create Screen + ViewModel + UiState Setting up data layer? → Read data layer section in architecture.md → Create Repository + DataSource + DAO Core Principles Offline-first : Local database is source of truth, sync with remote Unidirectional data flow : Events flow down, data flows up Reactive streams : Use Kotlin Flow for all data exposure Modular by feature : Each feature is self-contained with clear boundaries Testable by design : Use interfaces and test doubles, no mocking libraries Architecture Layers ┌─────────────────────────────────────────┐ │ UI Layer │ │ (Compose Screens + ViewModels) │ ├─────────────────────────────────────────┤ │ Domain Layer │ │ (Use Cases - optional, for reuse) │ ├─────────────────────────────────────────┤ │ Data Layer │ │ (Repositories + DataSources) │ └─────────────────────────────────────────┘ Module Types app/ # App module - navigation, scaffolding feature/ ├── featurename/ │ ├── api/ # Navigation keys (public) │ └── impl/ # Screen, ViewModel, DI (internal) core/ ├── data/ # Repositories ├── database/ # Room DAOs, entities ├── network/ # Retrofit, API models ├── model/ # Domain models (pure Kotlin) ├── common/ # Shared utilities ├── ui/ # Reusable Compose components ├── designsystem/ # Theme, icons, base components ├── datastore/ # Preferences storage └── testing/ # Test utilities Creating a New Feature Create feature:myfeature:api module with navigation key Create feature:myfeature:impl module with: MyFeatureScreen.kt - Composable UI MyFeatureViewModel.kt - State holder MyFeatureUiState.kt - Sealed interface for states MyFeatureNavigation.kt - Navigation setup MyFeatureModule.kt - Hilt DI module Standard File Patterns ViewModel Pattern @HiltViewModel class MyFeatureViewModel @Inject constructor ( private val myRepository: MyRepository, ) : ViewModel() { val uiState: StateFlow<MyFeatureUiState> = myRepository .getData() .map { data -> MyFeatureUiState.Success( data ) } .stateIn( scope = viewModelScope, started = SharingStarted.WhileSubscribed( 5_000 ), initialValue = MyFeatureUiState.Loading, ) fun onAction (action: MyFeatureAction ) { when (action) { is MyFeatureAction.ItemClicked -> handleItemClick(action.id) } } } UiState Pattern sealed interface MyFeatureUiState { data object Loading : MyFeatureUiState data class Success ( val items: List<Item>) : MyFeatureUiState data class Error ( val message: String) : MyFeatureUiState } Screen Pattern @Composable internal fun MyFeatureRoute ( onNavigateToDetail: ( String ) -> Unit , viewModel: MyFeatureViewModel = hiltViewModel() , ) { val uiState by viewModel.uiState.collectAsStateWithLifecycle() MyFeatureScreen( uiState = uiState, onAction = viewModel::onAction, onNavigateToDetail = onNavigateToDetail, ) } @Composable internal fun MyFeatureScreen ( uiState: MyFeatureUiState , onAction: ( MyFeatureAction ) -> Unit , onNavigateToDetail: ( String ) -> Unit , ) { when (uiState) { is MyFeatureUiState.Loading -> LoadingIndicator() is MyFeatureUiState.Success -> ContentList(uiState.items, onAction) is MyFeatureUiState.Error -> ErrorMessage(uiState.message) } } Repository Pattern interface MyRepository { fun getData () : Flow<List<MyModel>> suspend fun updateItem (id: String , data : MyModel ) } internal class OfflineFirstMyRepository @Inject constructor ( private val localDataSource: MyDao, private val networkDataSource: MyNetworkApi, ) : MyRepository { override fun getData () : Flow<List<MyModel>> = localDataSource.getAll().map { entities -> entities.map { it.toModel() } } override suspend fun updateItem (id: String , data : MyModel ) { localDataSource.upsert( data .toEntity()) } } Key Dependencies // Gradle version catalog (libs.versions.toml) [versions] kotlin = "1.9.x" compose-bom = "2024.x.x" hilt = "2.48" room = "2.6.x" coroutines = "1.7.x" [libraries] androidx-compose-bom = { group = "androidx.compose" , name = "compose-bom" , version.ref = "compose-bom" } hilt-android = { group = "com.google.dagger" , name = "hilt-android" , version.ref = "hilt" } room-runtime = { group = "androidx.room" , name = "room-runtime" , version.ref = "room" } Build Configuration Use convention plugins in build-logic/ for consistent configuration: AndroidApplicationConventionPlugin - App modules AndroidLibraryConventionPlugin - Library modules AndroidFeatureConventionPlugin - Feature modules AndroidComposeConventionPlugin - Compose setup AndroidHiltConventionPlugin - Hilt setup See gradle-setup.md for complete build configuration.