android-kotlin

Android Kotlin development with Coroutines, Jetpack Compose, Hilt, and MockK testing

Quality

45%

Does it follow best practices?

Impact

Pending

No eval scenarios have been run

Securityby

Passed

No known issues

Optimize this skill with Tessl

npx tessl skill review --optimize ./skills/android-kotlin/SKILL.md

Android Kotlin Skill

Load with: base.md

Project Structure

project/
├── app/
│   ├── src/
│   │   ├── main/
│   │   │   ├── kotlin/com/example/app/
│   │   │   │   ├── data/               # Data layer
│   │   │   │   │   ├── local/          # Room database
│   │   │   │   │   ├── remote/         # Retrofit/Ktor services
│   │   │   │   │   └── repository/     # Repository implementations
│   │   │   │   ├── di/                 # Hilt modules
│   │   │   │   ├── domain/             # Business logic
│   │   │   │   │   ├── model/          # Domain models
│   │   │   │   │   ├── repository/     # Repository interfaces
│   │   │   │   │   └── usecase/        # Use cases
│   │   │   │   ├── ui/                 # Presentation layer
│   │   │   │   │   ├── feature/        # Feature screens
│   │   │   │   │   │   ├── FeatureScreen.kt      # Compose UI
│   │   │   │   │   │   └── FeatureViewModel.kt
│   │   │   │   │   ├── components/     # Reusable Compose components
│   │   │   │   │   └── theme/          # Material theme
│   │   │   │   └── App.kt              # Application class
│   │   │   ├── res/
│   │   │   └── AndroidManifest.xml
│   │   ├── test/                       # Unit tests
│   │   └── androidTest/                # Instrumentation tests
│   └── build.gradle.kts
├── build.gradle.kts                    # Project-level build file
├── gradle.properties
├── settings.gradle.kts
└── CLAUDE.md

Gradle Configuration (Kotlin DSL)

App-level build.gradle.kts

plugins {
    id("com.android.application")
    id("org.jetbrains.kotlin.android")
    id("com.google.dagger.hilt.android")
    id("com.google.devtools.ksp")
}

android {
    namespace = "com.example.app"
    compileSdk = 34

    defaultConfig {
        applicationId = "com.example.app"
        minSdk = 24
        targetSdk = 34
        versionCode = 1
        versionName = "1.0"

        testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
    }

    buildTypes {
        release {
            isMinifyEnabled = true
            proguardFiles(
                getDefaultProguardFile("proguard-android-optimize.txt"),
                "proguard-rules.pro"
            )
        }
    }

    compileOptions {
        sourceCompatibility = JavaVersion.VERSION_17
        targetCompatibility = JavaVersion.VERSION_17
    }

    kotlinOptions {
        jvmTarget = "17"
    }

    buildFeatures {
        compose = true
    }

    composeOptions {
        kotlinCompilerExtensionVersion = "1.5.8"
    }
}

dependencies {
    // Compose BOM
    val composeBom = platform("androidx.compose:compose-bom:2024.01.00")
    implementation(composeBom)
    implementation("androidx.compose.ui:ui")
    implementation("androidx.compose.ui:ui-tooling-preview")
    implementation("androidx.compose.material3:material3")
    implementation("androidx.activity:activity-compose:1.8.2")
    implementation("androidx.lifecycle:lifecycle-viewmodel-compose:2.7.0")

    // Coroutines
    implementation("org.jetbrains.kotlinx:kotlinx-coroutines-android:1.7.3")

    // Hilt
    implementation("com.google.dagger:hilt-android:2.50")
    ksp("com.google.dagger:hilt-compiler:2.50")
    implementation("androidx.hilt:hilt-navigation-compose:1.1.0")

    // Room
    implementation("androidx.room:room-runtime:2.6.1")
    implementation("androidx.room:room-ktx:2.6.1")
    ksp("androidx.room:room-compiler:2.6.1")

    // Testing
    testImplementation("junit:junit:4.13.2")
    testImplementation("io.mockk:mockk:1.13.9")
    testImplementation("org.jetbrains.kotlinx:kotlinx-coroutines-test:1.7.3")
    testImplementation("app.cash.turbine:turbine:1.0.0")
    androidTestImplementation("androidx.test.ext:junit:1.1.5")
    androidTestImplementation("androidx.compose.ui:ui-test-junit4")
    debugImplementation("androidx.compose.ui:ui-tooling")
    debugImplementation("androidx.compose.ui:ui-test-manifest")
}

Kotlin Coroutines & Flow

ViewModel with StateFlow

@HiltViewModel
class UserViewModel @Inject constructor(
    private val getUserUseCase: GetUserUseCase,
    private val savedStateHandle: SavedStateHandle
) : ViewModel() {

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

    private val userId: String = checkNotNull(savedStateHandle["userId"])

    init {
        loadUser()
    }

    fun loadUser() {
        viewModelScope.launch {
            _uiState.update { it.copy(isLoading = true) }

            getUserUseCase(userId)
                .catch { e ->
                    _uiState.update {
                        it.copy(isLoading = false, error = e.message)
                    }
                }
                .collect { user ->
                    _uiState.update {
                        it.copy(isLoading = false, user = user, error = null)
                    }
                }
        }
    }

    fun clearError() {
        _uiState.update { it.copy(error = null) }
    }
}

data class UserUiState(
    val user: User? = null,
    val isLoading: Boolean = false,
    val error: String? = null
)

Repository with Flow

interface UserRepository {
    fun getUser(userId: String): Flow<User>
    fun observeUsers(): Flow<List<User>>
    suspend fun saveUser(user: User)
}

class UserRepositoryImpl @Inject constructor(
    private val api: UserApi,
    private val dao: UserDao,
    private val dispatcher: CoroutineDispatcher = Dispatchers.IO
) : UserRepository {

    override fun getUser(userId: String): Flow<User> = flow {
        // Emit cached data first
        dao.getUserById(userId)?.let { emit(it) }

        // Fetch from network and update cache
        val remoteUser = api.getUser(userId)
        dao.insert(remoteUser)
        emit(remoteUser)
    }.flowOn(dispatcher)

    override fun observeUsers(): Flow<List<User>> =
        dao.observeAllUsers().flowOn(dispatcher)

    override suspend fun saveUser(user: User) = withContext(dispatcher) {
        api.saveUser(user)
        dao.insert(user)
    }
}

Jetpack Compose

Screen with ViewModel

@Composable
fun UserScreen(
    viewModel: UserViewModel = hiltViewModel(),
    onNavigateBack: () -> Unit
) {
    val uiState by viewModel.uiState.collectAsStateWithLifecycle()

    UserScreenContent(
        uiState = uiState,
        onRefresh = viewModel::loadUser,
        onErrorDismiss = viewModel::clearError,
        onNavigateBack = onNavigateBack
    )
}

@Composable
private fun UserScreenContent(
    uiState: UserUiState,
    onRefresh: () -> Unit,
    onErrorDismiss: () -> Unit,
    onNavigateBack: () -> Unit
) {
    Scaffold(
        topBar = {
            TopAppBar(
                title = { Text("User Profile") },
                navigationIcon = {
                    IconButton(onClick = onNavigateBack) {
                        Icon(Icons.AutoMirrored.Filled.ArrowBack, "Back")
                    }
                }
            )
        }
    ) { padding ->
        Box(
            modifier = Modifier
                .fillMaxSize()
                .padding(padding)
        ) {
            when {
                uiState.isLoading -> {
                    CircularProgressIndicator(
                        modifier = Modifier.align(Alignment.Center)
                    )
                }
                uiState.user != null -> {
                    UserContent(user = uiState.user)
                }
            }

            uiState.error?.let { error ->
                Snackbar(
                    modifier = Modifier.align(Alignment.BottomCenter),
                    action = {
                        TextButton(onClick = onErrorDismiss) {
                            Text("Dismiss")
                        }
                    }
                ) {
                    Text(error)
                }
            }
        }
    }
}

Sealed Classes for State

Result Wrapper

sealed interface Result<out T> {
    data class Success<T>(val data: T) : Result<T>
    data class Error(val exception: Throwable) : Result<Nothing>
    data object Loading : Result<Nothing>
}

fun <T> Result<T>.getOrNull(): T? = (this as? Result.Success)?.data

inline fun <T, R> Result<T>.map(transform: (T) -> R): Result<R> = when (this) {
    is Result.Success -> Result.Success(transform(data))
    is Result.Error -> this
    is Result.Loading -> this
}

Testing with MockK & Turbine

ViewModel Tests

@OptIn(ExperimentalCoroutinesApi::class)
class UserViewModelTest {

    @get:Rule
    val mainDispatcherRule = MainDispatcherRule()

    private val getUserUseCase: GetUserUseCase = mockk()
    private val savedStateHandle = SavedStateHandle(mapOf("userId" to "123"))

    private lateinit var viewModel: UserViewModel

    @Before
    fun setup() {
        viewModel = UserViewModel(getUserUseCase, savedStateHandle)
    }

    @Test
    fun `loadUser success updates state with user`() = runTest {
        val user = User("123", "John Doe", "john@example.com")
        coEvery { getUserUseCase("123") } returns flowOf(user)

        viewModel.uiState.test {
            val initial = awaitItem()
            assertFalse(initial.isLoading)

            viewModel.loadUser()

            val loading = awaitItem()
            assertTrue(loading.isLoading)

            val success = awaitItem()
            assertFalse(success.isLoading)
            assertEquals(user, success.user)
        }
    }
}

class MainDispatcherRule(
    private val dispatcher: TestDispatcher = UnconfinedTestDispatcher()
) : TestWatcher() {
    override fun starting(description: Description) {
        Dispatchers.setMain(dispatcher)
    }
    override fun finished(description: Description) {
        Dispatchers.resetMain()
    }
}

GitHub Actions

name: Android Kotlin CI

on:
  push:
    branches: [main]
  pull_request:
    branches: [main]

jobs:
  build:
    runs-on: ubuntu-latest

    steps:
      - uses: actions/checkout@v4

      - name: Set up JDK 17
        uses: actions/setup-java@v4
        with:
          java-version: '17'
          distribution: 'temurin'

      - name: Setup Gradle
        uses: gradle/actions/setup-gradle@v3

      - name: Run Detekt
        run: ./gradlew detekt

      - name: Run Ktlint
        run: ./gradlew ktlintCheck

      - name: Run Unit Tests
        run: ./gradlew testDebugUnitTest

      - name: Build Debug APK
        run: ./gradlew assembleDebug

Lint Configuration

detekt.yml

build:
  maxIssues: 0

complexity:
  LongMethod:
    threshold: 20
  LongParameterList:
    functionThreshold: 4
  TooManyFunctions:
    thresholdInFiles: 10

style:
  MaxLineLength:
    maxLineLength: 120
  WildcardImport:
    active: true

coroutines:
  GlobalCoroutineUsage:
    active: true

Kotlin Anti-Patterns

❌ Blocking coroutines on Main - Never use runBlocking on main thread
❌ GlobalScope usage - Use structured concurrency with viewModelScope/lifecycleScope
❌ Collecting flows in init - Use repeatOnLifecycle or collectAsStateWithLifecycle
❌ Mutable state exposure - Expose StateFlow not MutableStateFlow
❌ Not handling exceptions in flows - Always use catch operator
❌ Lateinit for nullable - Use lazy or nullable with ?
❌ Hardcoded dispatchers - Inject dispatchers for testability
❌ Not using sealed classes - Prefer sealed for finite state sets
❌ Side effects in Composables - Use LaunchedEffect/SideEffect
❌ Unstable Compose parameters - Use stable/immutable types or @Stable

Repository: alinaqi/claude-bootstrap
Commit: d4ddb03

Last updated: 4 days ago
Created: 4 days ago

Is this your skill?

If you maintain this skill, you can claim it as your own. Once claimed, you can manage eval scenarios, bundle related skills, attach documentation or rules, and ensure cross-agent compatibility.