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At a glance
What it is
Expert Android/Kotlin development covering Jetpack Compose, MVVM architecture, Room database, Retrofit/OkHttp, Coroutines/Flow, WorkManager, Navigation component, Hilt dependency injection, ProGuard, and Play Store guidelines.
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SKILL.md
459 lines · 1,604 words
This skill provides comprehensive expertise in building modern Android applications using Kotlin. It covers Jetpack Compose UI development, clean architecture with MVVM, data persistence with Room, networking with Retrofit, reactive programming with Coroutines and Flow, background processing, dependency injection with Hilt, code shrinking, and Play Store compliance.
Expert Android/Kotlin development covering Jetpack Compose, MVVM architecture, Room database, Retrofit/OkHttp, Coroutines/Flow, WorkManager, Navigation component, Hilt dependency injection, ProGuard, and Play Store guidelines.
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What it covers
Overview
Project Architecture
Jetpack Compose
MVVM ViewModel
Room Database
Retrofit / OkHttp Networking
Coroutines and Flow
WorkManager for Background Tasks
Navigation Component with Compose
Hilt Dependency Injection
ProGuard / R8 Configuration
Play Store Guidelines Summary
Production Checklist
When to Use
Output Format
Example
Edge Cases
app/
├── di/ # Hilt modules
│ ├── AppModule.kt
│ ├── NetworkModule.kt
│ └── DatabaseModule.kt
├── data/
│ ├── local/
│ │ ├── dao/ # Room DAOs
│ │ ├── entity/ # Room entities
│ │ └── AppDatabase.kt
│ ├── remote/
│ │ ├── api/ # Retrofit interfaces
│ │ ├── dto/ # Data transfer objects
│ │ └── interceptor/ # OkHttp interceptors
│ └── repository/ # Repository implementations
├── domain/
│ ├── model/ # Business models
│ ├── repository/ # Repository interfaces
# ... (condensed) ...
│ ├── home/
│ │ ├── HomeScreen.kt
│ │ └── HomeViewModel.kt
│ ├── detail/
│ └── settings/
├── util/ # Extension functions, helpers
└── MyApplication.kt # @HiltAndroidApp@Composable
fun ProductListScreen(
viewModel: ProductListViewModel = hiltViewModel(),
onProductClick: (String) -> Unit,
) {
val uiState by viewModel.uiState.collectAsStateWithLifecycle()
Scaffold(
topBar = {
TopAppBar(
title = { Text("Products") },
actions = {
IconButton(onClick = viewModel::refresh) {
Icon(Icons.Default.Refresh, contentDescription = "Refresh")
}
}
)
}
# ... (condensed) ...
onRetry = viewModel::refresh,
modifier = Modifier.padding(padding)
)
}
}
}
}@Composable
fun ProductCard(
product: Product,
onClick: () -> Unit,
modifier: Modifier = Modifier,
) {
Card(
onClick = onClick,
modifier = modifier.fillMaxWidth(),
elevation = CardDefaults.cardElevation(defaultElevation = 2.dp),
) {
Row(
modifier = Modifier.padding(16.dp),
horizontalArrangement = Arrangement.spacedBy(12.dp),
) {
AsyncImage(
model = ImageRequest.Builder(LocalContext.current)
.data(product.imageUrl)
# ... (condensed) ...
style = MaterialTheme.typography.bodyLarge,
color = MaterialTheme.colorScheme.primary,
)
}
}
}
}@HiltViewModel
class ProductListViewModel @Inject constructor(
private val getProductsUseCase: GetProductsUseCase,
private val savedStateHandle: SavedStateHandle,
) : ViewModel() {
private val _uiState = MutableStateFlow<ProductUiState>(ProductUiState.Loading)
val uiState: StateFlow<ProductUiState> = _uiState.asStateFlow()
private val categoryId: String = savedStateHandle["categoryId"] ?: "all"
init {
loadProducts()
}
fun refresh() {
loadProducts()
}
# ... (condensed) ...
}
sealed interface ProductUiState {
data object Loading : ProductUiState
data class Success(val products: List<Product>) : ProductUiState
data class Error(val message: String) : ProductUiState
}// Entity
@Entity(tableName = "products")
data class ProductEntity(
@PrimaryKey val id: String,
val name: String,
val description: String,
val price: Double,
@ColumnInfo(name = "image_url") val imageUrl: String?,
@ColumnInfo(name = "category_id") val categoryId: String,
@ColumnInfo(name = "updated_at") val updatedAt: Long = System.currentTimeMillis(),
)
// DAO
@Dao
interface ProductDao {
@Query("SELECT * FROM products ORDER BY name ASC")
fun observeAll(): Flow<List<ProductEntity>>
# ... (condensed) ...
exportSchema = true,
)
@TypeConverters(Converters::class)
abstract class AppDatabase : RoomDatabase() {
abstract fun productDao(): ProductDao
abstract fun categoryDao(): CategoryDao
}// API interface
interface ProductApi {
@GET("products")
suspend fun getProducts(
@Query("category") categoryId: String? = null,
@Query("page") page: Int = 1,
@Query("limit") limit: Int = 20,
): ApiResponse<List<ProductDto>>
@GET("products/{id}")
suspend fun getProduct(@Path("id") id: String): ApiResponse<ProductDto>
@POST("products")
suspend fun createProduct(@Body product: CreateProductRequest): ApiResponse<ProductDto>
@Multipart
@POST("products/{id}/image")
suspend fun uploadImage(
# ... (condensed) ...
.build()
@Provides
@Singleton
fun provideProductApi(retrofit: Retrofit): ProductApi =
retrofit.create(ProductApi::class.java)
}class ProductRepositoryImpl @Inject constructor(
private val api: ProductApi,
private val dao: ProductDao,
private val dispatcher: CoroutineDispatcher = Dispatchers.IO,
) : ProductRepository {
supersede fun getProducts(categoryId: String): Flow<List<Product>> = flow {
// Emit cached data first
emitAll(
dao.observeByCategory(categoryId).map { entities ->
entities.map { it.toDomain() }
}
)
}.onStart {
// Trigger network refresh in background
try {
val response = withContext(dispatcher) {
api.getProducts(categoryId)
# ... (condensed) ...
}.recoverCatching {
// Fallback to cache
dao.getById(id)?.toDomain()
?: throw ProductNotFoundException(id)
}
}
}@HiltWorker
class SyncWorker @AssistedInject constructor(
@Assisted context: Context,
@Assisted params: WorkerParameters,
private val repository: ProductRepository,
) : CoroutineWorker(context, params) {
supersede suspend fun doWork(): Result {
return try {
repository.syncPendingChanges()
Result.success()
} catch (e: Exception) {
if (runAttemptCount < 3) {
Result.retry()
} else {
Result.failure(workDataOf("error" to e.message))
}
}
# ... (condensed) ...
"product_sync",
ExistingPeriodicWorkPolicy.KEEP,
request,
)
}
}
}// Routes
@Serializable data object Home
@Serializable data object Search
@Serializable data class ProductDetail(val productId: String)
@Serializable data class CategoryProducts(val categoryId: String, val title: String)
// NavHost
@Composable
fun AppNavigation(navController: NavHostController = rememberNavController()) {
NavHost(navController = navController, startDestination = Home) {
composable<Home> {
HomeScreen(
onProductClick = { id -> navController.navigate(ProductDetail(id)) },
onCategoryClick = { id, title ->
navController.navigate(CategoryProducts(id, title))
},
onSearchClick = { navController.navigate(Search) },
)
# ... (condensed) ...
title = args.title,
onProductClick = { id -> navController.navigate(ProductDetail(id)) },
onBack = { navController.popBackStack() },
)
}
}
}@HiltAndroidApp
class MyApplication : Application()
// App-level module
@Module
@InstallIn(SingletonComponent::class)
object AppModule {
@Provides
@Singleton
fun provideAppDatabase(@ApplicationContext context: Context): AppDatabase =
Room.databaseBuilder(context, AppDatabase::class.java, "myapp.db")
.addMigrations(MIGRATION_2_3)
.build()
@Provides
fun provideProductDao(db: AppDatabase): ProductDao = db.productDao()
}
# ... (condensed) ...
// Use case injection
class GetProductsUseCase @Inject constructor(
private val repository: ProductRepository,
) {
operator fun invoke(categoryId: String): Flow<List<Product>> =
repository.getProducts(categoryId)
}# proguard-rules.pro
# Keep data classes used with Moshi/Gson
-keep class com.myapp.data.remote.dto.** { *; }
-keep class com.myapp.data.local.entity.** { *; }
# Moshi
-keepclassmembers class * {
@com.squareup.moshi.Json <fields>;
}
-keep @com.squareup.moshi.JsonQualifier @interface *
# Retrofit
-keepattributes Signature
-keepattributes Exceptions
-keepclassmembers,allowshrinking,allowobfuscation interface * {
@retrofit2.http.* <methods>;
}
# ... (condensed) ...
-keepclassmembers class * implements android.os.Parcelable {
public static final ** CREATOR;
}
# Debugging - keep source file names and line numbers
-keepattributes SourceFile,LineNumberTable
-renamesourcefileattribute SourceFile| Issue | Policy | Prevention |
|---|---|---|
| Crashes on review device | Functionality | Test on Pixel devices and various API levels |
| Missing privacy policy | User Data | Link privacy policy in Store listing and in-app |
| Deceptive behavior | Deceptive Behavior | App must do what listing describes |
| Inappropriate content | Content | Implement content rating questionnaire honestly |
| Background battery drain | Background Limits | Use WorkManager, respect Doze mode |
| Excessive permissions | Permissions | Request only what you need, explain why |
| Missing data deletion | Data Deletion | Provide account/data deletion mechanism |
| Target API level | Target API Level | Must target latest required API level |
Target the latest required API level
Configure R8 / ProGuard rules and test release build
Set up crash reporting (Firebase Crashlytics)
Implement ANR-free architecture (no main thread blocking)
Test on multiple screen sizes and densities
Configure Baseline Profiles for startup performance
Set up CI/CD with GitHub Actions or Bitrise
Complete Play Store listing with screenshots for all form factors
Implement proper back navigation and deep links
Verify ProGuard mappings are uploaded for crash deobfuscation
Test accessibility with TalkBack
Configure App Signing by Google Play
Verify data deletion flow works correctly
Test in-app updates and in-app reviews integration
Profile startup time and optimize cold start
Use this skill when:
Designing or implementing android developer solutions
Reviewing or improving existing android developer approaches
Making architectural or implementation decisions about android developer
Learning android developer patterns and best practices
Troubleshooting android developer-related issues
Do NOT use this skill when:
The question is about a fundamentally different technology domain
A more specific sibling skill covers the exact topic needed
The user needs a complete hands-on tutorial rather than expert guidance
# Android Developer Analysis
## Context Assessment
[Situation summary and constraints]
## Recommended Approach
[Primary recommendation with rationale]
## Implementation Steps
1. [Step with specific details]
2. [Step with specific details]
3. [Step with specific details]
## Trade-offs and Considerations
- [Key trade-off 1]
- [Key trade-off 2]
## Next Steps
- [Immediate action item]
- [Follow-up action item]Input: "Help me implement android developer for a medium-scale production application"
Output: A structured analysis covering current state assessment, recommended android developer approach with specific patterns, implementation roadmap with milestones, and risk mitigation strategies tailored to the application scale and constraints.
Legacy system integration: When android developer must coexist with legacy approaches, provide a gradual migration path rather than a complete rewrite
Scale mismatch: When the solution complexity exceeds the project scale, recommend a simpler approach and note when to revisit
Team skill gaps: When the team lacks experience with the recommended approach, include learning resources and simpler alternatives
Conflicting requirements: When constraints conflict (e.g., performance vs. maintainability), explicitly state the trade-off and recommend based on stated priorities
SKILL.md
459 lines · 1,604 words
The text of SKILL.md is shown as it downloads, under the Apache-2.0 license, by Ferrox Labs. The license is the one in the file's own frontmatter.
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