ABOUTME: Android/Kotlin - Compose, architecture, testing, performance

ABOUTME: Kotlin 2.x, Compose 1.7+, type-safe navigation, Baseline Profiles

Android/Kotlin

Commands

./gradlew assembleDebug|assembleRelease|test|connectedAndroidTest|lint|ktlintFormat
./gradlew :feature:home:build                    # Module-specific

See: _AST_GREP.md (sg patterns) | _PATTERNS.md | source-control

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Architecture

Clean Architecture Structure

feature/
├── data/repository/, datasource/local/, datasource/remote/
├── domain/model/, repository/ (interface), usecase/
└── presentation/screen/, viewmodel/

Use Cases

Single responsibility, orchestration here (NOT in ViewModel).

class SignInUseCase(private val auth: AuthRepository, private val user: UserRepository) {
    suspend operator fun invoke(email: String, password: String): Result<User> {
        val result = auth.signIn(email, password).getOrElse { return Result.failure(it) }
        user.saveUserLocally(result)
        return Result.success(result)
    }
}

ViewModel Pattern

class FeedViewModel(private val getFeed: GetFeedUseCase) : ViewModel() {
    private val _uiState = MutableStateFlow<FeedUiState>(FeedUiState.Loading)
    val uiState = _uiState.asStateFlow()

    private val _sideEffects = Channel<FeedSideEffect>(Channel.BUFFERED)
    val sideEffects = _sideEffects.receiveAsFlow()

    fun loadFeed() = viewModelScope.launch {
        _uiState.value = FeedUiState.Loading
        getFeed().onSuccess { _uiState.value = FeedUiState.Success(it) }
                 .onFailure { _uiState.value = FeedUiState.Error(it.message) }
    }
}

sealed interface FeedUiState { /* Loading, Success, Error */ }
sealed interface FeedSideEffect { /* NavigateToDetail, ShowSnackbar */ }

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Dependency Injection

Aspect	Hilt	Koin
Type	Compile-time	Runtime
Build time	Slower	Faster
Error detection	Compile	Runtime
KMP support	No	Yes
Best for	Large/enterprise	Small-medium/KMP

Hilt: @HiltAndroidApp, @AndroidEntryPoint, @HiltViewModel, @Inject constructor Koin: module { }, single, factory, viewModelOf, koinViewModel()

See references/compose-patterns.md for setup examples.

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Compose Essentials

State hoisting: Lift state to the caller, pass callbacks down.

@Composable
fun UserCard(user: User, onClick: () -> Unit, modifier: Modifier = Modifier) {
    Card(onClick = onClick, modifier = modifier) { /* content */ }
}

State management:

• remember { mutableStateOf() }, lost on config change
• rememberSaveable { mutableStateOf() }, survives config change
• derivedStateOf, computed state

Side effects: LaunchedEffect(key), DisposableEffect

Type-safe navigation: @Serializable routes (2.8.0+)

See references/compose-patterns.md for detailed examples.

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Code Review Checklists

Architecture

• VMs don't chain use cases (orchestration in domain)
• VMs don't call repositories directly
• Use cases have single responsibility
• State immutable (use copy())
• Side effects use Channel/SharedFlow (not StateFlow)

Compose

• State hoisted appropriately
• remember vs rememberSaveable correct
• Side effects use correct APIs
• Stable types for parameters
• key used in LazyColumn/LazyRow

Red Flags

Critical	High
Network/DB on main thread	Use case chaining in VM
StateFlow for one-time events	Mutable state exposed from VM
Hardcoded strings in UI	Missing key in LazyColumn
Missing error handling	collectAsState vs collectAsStateWithLifecycle
R8 disabled in release

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Quick Reference

Kotlin 2.x features: Guard conditions (2.1), context parameters (2.2), K2 compiler benefits → references/kotlin-features.md

Compose patterns: State, side effects, navigation, image loading → references/compose-patterns.md

Networking & Data: Retrofit, Ktor, Room, DataStore → references/data-layer.md

Testing: Compose UI tests, ViewModel tests, snapshot tests → references/testing-patterns.md

Performance: R8, Baseline Profiles, Compose optimization → references/performance.md

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Resources

Official: android.com/kotlin | compose | architecture | type-safe nav | baseline profiles

Kotlin: 2.2 | 2.1.20 | 2.3

Libraries: Coil | Koin | Hilt | Retrofit | Ktor | Room

Testing: Compose testing | Paparazzi | Turbine