---

name: android description: > Use this skill when the user asks about Android development, Kotlin, Jetpack Compose, Android architecture, MVVM, Clean Architecture, Room, Hilt, Retrofit, or Android testing. version: "2.0.0" author: "j4flmao" license: "MIT" compatibility: claude-code: true cursor: true codex: true windsurf: true tags: [mobile, android, phase-4]

Android Native

Purpose

Implement Android native applications using Kotlin, Jetpack Compose, MVVM+Clean Architecture, Coroutines+Flow, Hilt DI, Room, and comprehensive testing.

Agent Protocol

Trigger

User request includes: android, kotlin, jetpack, compose, android architecture, android testing, room, hilt.

Input Context

• Android SDK version (compileSdk / minSdk / targetSdk)
• Kotlin version
• Build system (Gradle KTS)
• Architecture pattern (MVVM, Clean, MVI)

Output Artifact

A markdown document containing:

• Project structure
• Jetpack Compose setup
• MVVM+Clean Architecture
• Coroutines+Flow concurrency
• Hilt dependency injection
• Room database setup
• JUnit + Espresso test plan

Response Format

Produce the artifact directly. No preamble, no postamble, no explanations. No filler, no hedging, no transitions. Strip articles a/an/the where unambiguous. Compress output — why use many token when few do trick.

Max Response Length

4096 tokens

Workflow

Step 1: Set Up Project Structure

Organize code with Clean Architecture layers: data, domain, ui, and di with feature-based packaging.

Step 2: Implement Domain Layer

Define domain models, repository interfaces, and use cases independent of framework dependencies.

Step 3: Implement Data Layer

Set up Room database with DAOs and entities, Retrofit API service, and repository implementations bridging local and remote sources.

Step 4: Configure Dependency Injection

Set up Hilt modules for database, network, and repository bindings with appropriate scopes.

Step 5: Build UI with Jetpack Compose

Create ViewModels with StateFlow, Compose screens with state collection, and handle loading/error/success states.

Step 6: Write Tests

Cover domain use cases with JUnit + MockK unit tests and UI screens with Compose + Espresso UI tests.

Architecture Decision Trees

Architecture Selection

App complexity?
├── Simple CRUD (<10 screens, no complex state)
│   → MVVM + Repository — ViewModel → Repository → API/DB
│   → No UseCase layer needed
├── Complex state (real-time, multi-step forms)
│   → MVI with sealed Intent/State classes, reducer pattern
│   → Single state object per screen
└── Large codebase (5+ teams, shared domain)
    → Clean Architecture with strict layer separation
    → Domain module shared across features

DI Strategy

Team preference?
├── Annotation-based → Hilt
│   Pros: compile-time verification, @HiltViewModel, less boilerplate
│   Cons: slower build, kapt/ksp overhead
├── Manual DI → Koin
│   Pros: no annotation processing, fast builds, easy to learn
│   Cons: runtime errors for missing bindings
└── Compiler-assisted → Dagger (raw)
    Pros: most control, mature
    Cons: steep learning curve, verbose

Navigation Approach

Single-activity?
├── Yes → Jetpack Navigation Compose
│   NavHost with sealed Route class, type-safe arguments
├── Multi-activity → Navigation component with XML
└── Feature-modules → Dynamic feature navigation with NavDeepLink

Image Loading Strategy

Network images needed?
├── Yes, Coil — Kotlin coroutines, Compose integration, memory-efficient
└── Yes, Glide — Mature, animated GIF/WebP, disk cache, OK
    Coil preferred for new projects — lighter (150KB vs ~500KB)

Background Work Strategy

WorkManager vs Foreground Service vs AlarmManager
├── Deferrable, reliable → WorkManager (constraints, chaining, battery-optimized)
├── User-visible must continue → Foreground Service (notification required)
└── Exact timing needed → AlarmManager (limited, consider ScheduleTaskExecutor)

Project Structure

app/
├── src/main/java/com/example/app/
│   ├── App.kt
│   ├── MainActivity.kt
│   ├── data/
│   │   ├── local/
│   │   │   ├── AppDatabase.kt
│   │   │   ├── OrderDao.kt
│   │   │   └── OrderEntity.kt
│   │   ├── remote/
│   │   │   ├── ApiService.kt
│   │   │   └── OrderResponse.kt
│   │   └── repository/
│   │       └── OrderRepositoryImpl.kt
│   ├── di/
│   │   ├── AppModule.kt
│   │   ├── DatabaseModule.kt
│   │   └── NetworkModule.kt
│   ├── domain/
│   │   ├── model/
│   │   │   └── Order.kt
│   │   ├── repository/
│   │   │   └── OrderRepository.kt
│   │   └── usecase/
│   │       └── GetOrdersUseCase.kt
│   └── ui/
│       ├── orders/
│       │   ├── OrderListScreen.kt
│       │   ├── OrderDetailScreen.kt
│       │   └── OrderViewModel.kt
│       └── theme/
└── src/test/
    └── ...

MVVM + Clean Architecture

// domain/model/Order.kt
data class Order(
    val id: String,
    val customerName: String,
    val total: Double,
    val status: OrderStatus
)

enum class OrderStatus { PENDING, SHIPPED, DELIVERED }

// domain/repository/OrderRepository.kt
interface OrderRepository {
    suspend fun getOrders(): Result<List<Order>>
    suspend fun getOrder(id: String): Result<Order>
}

// domain/usecase/GetOrdersUseCase.kt
class GetOrdersUseCase(private val repo: OrderRepository) {
    suspend operator fun invoke(): Result<List<Order>> = repo.getOrders()
}

Jetpack Compose UI

// ui/orders/OrderViewModel.kt
@HiltViewModel
class OrderViewModel @Inject constructor(
    private val getOrders: GetOrdersUseCase
) : ViewModel() {
    private val _state = MutableStateFlow<OrderUiState>(OrderUiState.Loading)
    val state: StateFlow<OrderUiState> = _state.asStateFlow()

    fun loadOrders() {
        viewModelScope.launch {
            _state.value = OrderUiState.Loading
            getOrders()
                .onSuccess { _state.value = OrderUiState.Success(it) }
                .onFailure { _state.value = OrderUiState.Error(it.message) }
        }
    }
}

sealed interface OrderUiState {
    data object Loading : OrderUiState
    data class Success(val orders: List<Order>) : OrderUiState
    data class Error(val message: String?) : OrderUiState
}

// ui/orders/OrderListScreen.kt
@Composable
fun OrderListScreen(
    viewModel: OrderViewModel = hiltViewModel(),
    onOrderClick: (String) -> Unit
) {
    val state by viewModel.state.collectAsStateWithLifecycle()

    LaunchedEffect(Unit) { viewModel.loadOrders() }

    when (val s = state) {
        is OrderUiState.Loading -> CircularProgressIndicator()
        is OrderUiState.Error -> ErrorMessage(s.message, onRetry = viewModel::loadOrders)
        is OrderUiState.Success -> LazyColumn {
            items(s.orders, key = { it.id }) { order ->
                OrderCard(order = order, onClick = { onOrderClick(order.id) })
            }
        }
    }
}

@Composable
fun OrderCard(order: Order, onClick: () -> Unit) {
    Card(modifier = Modifier.clickable(onClick = onClick)) {
        Column(modifier = Modifier.padding(16.dp)) {
            Text(text = order.customerName, style = MaterialTheme.typography.titleMedium)
            Text(text = "${order.total}", style = MaterialTheme.typography.bodyLarge)
        }
    }
}

Room Database

// data/local/OrderEntity.kt
@Entity(tableName = "orders")
data class OrderEntity(
    @PrimaryKey val id: String,
    @ColumnInfo(name = "customer_name") val customerName: String,
    val total: Double,
    val status: String
)

// data/local/OrderDao.kt
@Dao
interface OrderDao {
    @Query("SELECT * FROM orders")
    fun getAll(): Flow<List<OrderEntity>>

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    suspend fun insertAll(orders: List<OrderEntity>)

    @Query("DELETE FROM orders WHERE id = :id")
    suspend fun deleteById(id: String)
}

// data/local/AppDatabase.kt
@Database(entities = [OrderEntity::class], version = 1, exportSchema = true)
abstract class AppDatabase : RoomDatabase() {
    abstract fun orderDao(): OrderDao
}

Hilt DI

// di/AppModule.kt
@Module
@InstallIn(SingletonComponent::class)
object AppModule {
    @Provides @Singleton
    fun provideOrderRepository(
        api: ApiService,
        dao: OrderDao
    ): OrderRepository = OrderRepositoryImpl(api, dao)
}

// di/NetworkModule.kt
@Module
@InstallIn(SingletonComponent::class)
object NetworkModule {
    @Provides @Singleton
    fun provideApiService(): ApiService {
        return Retrofit.Builder()
            .baseUrl("https://api.example.com/")
            .addConverterFactory(MoshiConverterFactory.create())
            .addCallAdapterFactory(CoroutineCallAdapterFactory())
            .client(OkHttpClient.Builder()
                .connectTimeout(30, TimeUnit.SECONDS)
                .readTimeout(30, TimeUnit.SECONDS)
                .addInterceptor(HttpLoggingInterceptor().apply {
                    level = if (BuildConfig.DEBUG) BODY else NONE
                })
                .build())
            .build()
            .create(ApiService::class.java)
    }
}

// di/DatabaseModule.kt
@Module
@InstallIn(SingletonComponent::class)
object DatabaseModule {
    @Provides @Singleton
    fun provideDatabase(@ApplicationContext ctx: Context): AppDatabase {
        return Room.databaseBuilder(ctx, AppDatabase::class.java, "app-db")
            .fallbackToDestructiveMigration()
            .build()
    }

    @Provides fun provideOrderDao(db: AppDatabase): OrderDao = db.orderDao()
}

Testing

Unit Test (JUnit + MockK)

class GetOrdersUseCaseTest {
    private val repo = mockk<OrderRepository>()
    private val useCase = GetOrdersUseCase(repo)

    @Test
    fun `returns orders successfully`() = runTest {
        val orders = listOf(Order("1", "Test", 100.0, OrderStatus.PENDING))
        coEvery { repo.getOrders() } returns Result.success(orders)

        val result = useCase()

        assertTrue(result.isSuccess)
        assertEquals(orders, result.getOrThrow())
    }

    @Test
    fun `returns failure when repository fails`() = runTest {
        coEvery { repo.getOrders() } returns Result.failure(IOException("Network error"))

        val result = useCase()

        assertTrue(result.isFailure)
        assertTrue(result.exceptionOrNull() is IOException)
    }
}

UI Test (Compose + Espresso)

@RunWith(AndroidJUnit4::class)
class OrderListScreenTest {
    @get:Rule
    val composeTestRule = createComposeRule()

    @Test
    fun displaysOrders() {
        val viewModel = mockk<OrderViewModel>()
        every { viewModel.state } returns MutableStateFlow(
            OrderUiState.Success(listOf(
                Order("1", "Alice", 50.0, OrderStatus.PENDING)
            ))
        ).asStateFlow()

        composeTestRule.setContent {
            OrderListScreen(viewModel = viewModel, onOrderClick = {})
        }

        composeTestRule.onNodeWithText("Alice").assertIsDisplayed()
    }

    @Test
    fun showsErrorState() {
        val viewModel = mockk<OrderViewModel>()
        every { viewModel.state } returns MutableStateFlow(
            OrderUiState.Error("Failed to load")
        ).asStateFlow()

        composeTestRule.setContent {
            OrderListScreen(viewModel = viewModel, onOrderClick = {})
        }

        composeTestRule.onNodeWithText("Failed to load").assertIsDisplayed()
    }
}

Compose Performance Patterns

// Stable data classes — Compose skips recomposition when inputs are stable
@Stable
data class OrderUiModel(val id: String, val name: String, val total: Double)

// derivedStateOf for expensive computations
val totalPrice by remember(orders) {
    derivedStateOf { orders.sumOf { it.total } }
}

// LazyColumn keys for stable identity
items(orders, key = { it.id }) { order -> OrderCard(order) }

// Remember lambda to avoid allocation on recomposition
val onItemClick = remember { { id: String -> onOrderClick(id) } }

// ContentType for list-item differentiation
items(orders, key = { it.id }, contentType = { "order" }) { ... }

Compose Modifier Best Practices

• Modifier order matters: size → padding → background → clickable (outer to inner)
• Klibs Modifier.composed for reusable modifier chains
• Avoid Modifier.absoluteOffset — prefer Modifier.offset for RTL support
• Modifier.clipToBounds() to prevent content overflow
• Modifier.alpha(0f) vs Modifier.visible(false) — invisible keeps layout space, gone releases it

Production Considerations

• ProGuard/R8 rules: keep @Keep annotations, Moshi adapters, Retrofit interfaces
• Network security config for certificate pinning
• Baseline Profiles for startup optimization (30%+ faster cold start)
• LeakCanary for memory leak detection in debug builds
• Chucker for network inspection in debug builds
• StrictMode for detecting disk/network on main thread during development
• App Startup library for ordered, lazy SDK initialization

Kotlin Coroutines & Flow Best Practices

• viewModelScope.launch for fire-and-forget operations (logging, analytics)
• viewModelScope.async for concurrent decomposition (parallel API calls)
• flatMapLatest for search-as-you-type debounced queries
• stateIn(WhileSubscribed(5000)) to keep upstream active for 5s after last subscriber
• catch { emit(UiState.Error(it)) } for error recovery in Flow chains
• Retrofit suspend functions are main-safe — no need to wrap with withContext(IO)
• Room DAO Flow automatically runs on background thread
• Dispatchers.IO for blocking operations, Dispatchers.Default for CPU-heavy work

Package Structure Options

Feature-first (recommended for medium+ apps):
com.example.app/
├── feature/orders/
│   ├── data/ local/ remote/ repository/
│   ├── domain/ model/ repository/ usecase/
│   └── ui/ OrderListScreen OrderViewModel
├── core/ network/ database/ di/ testing/

Layer-first (simple apps):
com.example.app/
├── data/
├── domain/
├── ui/
└── di/

Anti-Patterns

• God ViewModels: ViewModel handling logic for multiple screens — split per screen
• Repository exposing raw data sources: Never return ApiResult or DbModel — map to domain models
• Hilt unscoped bindings: Always declare scope — unscoped = new instance every injection
• CollectAsState instead of collectAsStateWithLifecycle: Without lifecycle awareness, collection leaks when screen is in background
• MutableStateFlow exposure: Expose as StateFlow, keep MutableStateFlow private
• Using GlobalScope: Never use GlobalScope.launch — creates leaked coroutines tied to app process
• Main thread DB access: Room on main thread throws — use suspend functions or Flow
• Ignoring configuration changes: State in ViewModel survives rotation; state in remember does not
• Deep layout hierarchy: Compose recomposes deeply nested layouts inefficiently — keep composable depth <10 levels

Rules

• Repository interfaces belong in domain layer; implementations in data layer
• ViewModels expose state via StateFlow, never expose mutable state
• Hilt modules must declare explicit scopes — no unscoped bindings for singletons
• Room operations on IO thread — use coroutine dispatchers or Room's built-in threading
• Compose screens collect StateFlow with collectAsStateWithLifecycle, not collectAsState
• Use sealed interfaces for UI state to represent loading, success, and error
• DI modules are in a separate package — never scatter provides across feature packages
• Baseline Profiles for all release builds targeting startup performance
• Compose Modifier order: size → padding → background → clickable (outside-in)
• Navigation routes defined in a single sealed class — never stringly-typed routes
• Image loading via Coil in Compose with AsyncImage or rememberAsyncImagePainter
• ProGuard rules must keep all Moshi/Retrofit/Kotlin serialization classes

References

• references/android-advanced.md — Android Advanced Topics
• references/android-architecture.md — Android Architecture — MVVM + Clean Architecture
• references/android-fundamentals.md — Android Fundamentals
• references/compose-performance.md — Jetpack Compose Performance Optimization
• references/hilt-di.md — Hilt Dependency Injection
• references/jetpack-compose.md — Jetpack Compose
• references/testing.md — Android Testing

Handoff

Hand off to mobile/universal/deployment/SKILL.md for deployment.