Android Kotlin

ABOUTME: Android/Kotlin, Compose, Clean Architecture, testing, performance

ABOUTME: MVVM + DI conventions, state/side-effect patterns, review checklists

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

Version (determine, don't assume)

See ../_LANG_COMMON.md. Fetch the truth:

./gradlew --version                                         # Gradle + JVM
grep -E 'kotlin|agp|compose' gradle/libs.versions.toml      # version catalog (preferred)
grep -E 'kotlin|android' build.gradle.kts                   # fallback
cat gradle.properties                                       # AGP / Kotlin flags
curl -s https://api.github.com/repos/JetBrains/kotlin/releases/latest | jq -r .tag_name   # latest Kotlin
curl -s https://api.github.com/repos/gradle/gradle/releases/latest | jq -r .tag_name      # latest Gradle

Pre-Commit Verification (MANDATORY)

make check && make test-e2e must pass (enforced by the pre-commit-gate hook; see ../_LANG_COMMON.md). What make check expands to for Android:

./gradlew ktlintCheck                           # formatting
./gradlew detekt                                # static analysis
./gradlew lint                                  # Android lint
./gradlew test                                  # unit tests (all variants)
./gradlew connectedAndroidTest                  # instrumented / e2e (device/emulator)

Architecture

Clean Architecture Structure

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

Use Cases and ViewModels

Use cases: single responsibility, orchestration here (NOT in ViewModel). ViewModels expose immutable StateFlow UI state and one-time events via Channel/SharedFlow (never StateFlow). For the full SignInUseCase + FeedViewModel + UiState/SideEffect code, see references/compose-patterns.md.

Dependency Injection

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

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

Compose Essentials

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

State APIs:

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

Side effects: LaunchedEffect(key), DisposableEffect. Collect flows with collectAsStateWithLifecycle() (not collectAsState).

Type-safe navigation: @Serializable routes.

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

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

Detailed References

• references/kotlin-features.md - Kotlin language features and idioms
• references/compose-patterns.md - State, side effects, navigation, image loading
• references/data-layer.md - Retrofit, Ktor, Room, DataStore
• references/testing-patterns.md - Compose UI tests, ViewModel tests, snapshot tests (Paparazzi), Turbine
• references/performance.md - R8, Baseline Profiles, Compose optimization

Resources

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

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

Testing: Compose testing | Paparazzi | Turbine