---
id: alinaqi/maggy/android-kotlin
version: "be81a40f"
license: MIT
install: manual
updated: 2026-07-14
---

# android-kotlin — This skill equips you to develop Android applications using Kotlin's modern ecosystem. Leverage Jetpack Compose for declarative UI, Coroutines for asynchronous programming, and Hilt for dependency injection to create robust, maintainable mobile apps.

Publisher: alinaqi · Stars: 703 · Updated: 2026-07-14

Install (manual): `git clone https://github.com/alinaqi/maggy`

## SKILL.md

# Android Kotlin Skill


---

## 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
```kotlin
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
```kotlin
@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
```kotlin
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
```kotlin
@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
```kotlin
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
```kotlin
@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

```yaml
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
```yaml
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`



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