---
name: android-development
description: Create production-quality Android applications following Google's official architecture guidance and NowInAndroid best practices. Use when building Android apps with Kotlin, Jetpack Compose, MVVM architecture, Hilt dependency injection, Room database, or multi-module projects. Triggers on requests to create Android projects, screens, ViewModels, repositories, feature modules, or when asked about Android architecture patterns.
---

# Android Development

Build Android applications following Google's official architecture guidance, as demonstrated in the NowInAndroid reference app.

## Quick Reference

| Task | Reference File |
|------|----------------|
| Project structure & modules | [modularization.md](references/modularization.md) |
| Architecture layers (UI, Domain, Data) | [architecture.md](references/architecture.md) |
| Jetpack Compose patterns | [compose-patterns.md](references/compose-patterns.md) |
| Gradle & build configuration | [gradle-setup.md](references/gradle-setup.md) |
| Testing approach | [testing.md](references/testing.md) |

## Workflow Decision Tree

**Creating a new project?**
→ Read [modularization.md](references/modularization.md) for project structure
→ Use templates in `assets/templates/`

**Adding a new feature?**
→ Create feature module with `api` and `impl` submodules
→ Follow patterns in [architecture.md](references/architecture.md)

**Building UI screens?**
→ Read [compose-patterns.md](references/compose-patterns.md)
→ Create Screen + ViewModel + UiState

**Setting up data layer?**
→ Read data layer section in [architecture.md](references/architecture.md)
→ Create Repository + DataSource + DAO

## Core Principles

1. **Offline-first**: Local database is source of truth, sync with remote
2. **Unidirectional data flow**: Events flow down, data flows up
3. **Reactive streams**: Use Kotlin Flow for all data exposure
4. **Modular by feature**: Each feature is self-contained with clear boundaries
5. **Testable by design**: Use interfaces and test doubles, no mocking libraries

## Architecture Layers

```
┌─────────────────────────────────────────┐
│              UI Layer                    │
│  (Compose Screens + ViewModels)          │
├─────────────────────────────────────────┤
│           Domain Layer                   │
│  (Use Cases - optional, for reuse)       │
├─────────────────────────────────────────┤
│            Data Layer                    │
│  (Repositories + DataSources)            │
└─────────────────────────────────────────┘
```

## Module Types

```
app/                    # App module - navigation, scaffolding
feature/
  ├── featurename/
  │   ├── api/          # Navigation keys (public)
  │   └── impl/         # Screen, ViewModel, DI (internal)
core/
  ├── data/             # Repositories
  ├── database/         # Room DAOs, entities
  ├── network/          # Retrofit, API models
  ├── model/            # Domain models (pure Kotlin)
  ├── common/           # Shared utilities
  ├── ui/               # Reusable Compose components
  ├── designsystem/     # Theme, icons, base components
  ├── datastore/        # Preferences storage
  └── testing/          # Test utilities
```

## Creating a New Feature

1. Create `feature:myfeature:api` module with navigation key
2. Create `feature:myfeature:impl` module with:
   - `MyFeatureScreen.kt` - Composable UI
   - `MyFeatureViewModel.kt` - State holder
   - `MyFeatureUiState.kt` - Sealed interface for states
   - `MyFeatureNavigation.kt` - Navigation setup
   - `MyFeatureModule.kt` - Hilt DI module

## Standard File Patterns

### ViewModel Pattern
```kotlin
@HiltViewModel
class MyFeatureViewModel @Inject constructor(
    private val myRepository: MyRepository,
) : ViewModel() {

    val uiState: StateFlow<MyFeatureUiState> = myRepository
        .getData()
        .map { data -> MyFeatureUiState.Success(data) }
        .stateIn(
            scope = viewModelScope,
            started = SharingStarted.WhileSubscribed(5_000),
            initialValue = MyFeatureUiState.Loading,
        )
    
    fun onAction(action: MyFeatureAction) {
        when (action) {
            is MyFeatureAction.ItemClicked -> handleItemClick(action.id)
        }
    }
}
```

### UiState Pattern
```kotlin
sealed interface MyFeatureUiState {
    data object Loading : MyFeatureUiState
    data class Success(val items: List<Item>) : MyFeatureUiState
    data class Error(val message: String) : MyFeatureUiState
}
```

### Screen Pattern
```kotlin
@Composable
internal fun MyFeatureRoute(
    onNavigateToDetail: (String) -> Unit,
    viewModel: MyFeatureViewModel = hiltViewModel(),
) {
    val uiState by viewModel.uiState.collectAsStateWithLifecycle()
    MyFeatureScreen(
        uiState = uiState,
        onAction = viewModel::onAction,
        onNavigateToDetail = onNavigateToDetail,
    )
}

@Composable
internal fun MyFeatureScreen(
    uiState: MyFeatureUiState,
    onAction: (MyFeatureAction) -> Unit,
    onNavigateToDetail: (String) -> Unit,
) {
    when (uiState) {
        is MyFeatureUiState.Loading -> LoadingIndicator()
        is MyFeatureUiState.Success -> ContentList(uiState.items, onAction)
        is MyFeatureUiState.Error -> ErrorMessage(uiState.message)
    }
}
```

### Repository Pattern
```kotlin
interface MyRepository {
    fun getData(): Flow<List<MyModel>>
    suspend fun updateItem(id: String, data: MyModel)
}

internal class OfflineFirstMyRepository @Inject constructor(
    private val localDataSource: MyDao,
    private val networkDataSource: MyNetworkApi,
) : MyRepository {

    override fun getData(): Flow<List<MyModel>> =
        localDataSource.getAll().map { entities ->
            entities.map { it.toModel() }
        }
    
    override suspend fun updateItem(id: String, data: MyModel) {
        localDataSource.upsert(data.toEntity())
    }
}
```

## Key Dependencies

```kotlin
// Gradle version catalog (libs.versions.toml)
[versions]
kotlin = "1.9.x"
compose-bom = "2024.x.x"
hilt = "2.48"
room = "2.6.x"
coroutines = "1.7.x"

[libraries]
androidx-compose-bom = { group = "androidx.compose", name = "compose-bom", version.ref = "compose-bom" }
hilt-android = { group = "com.google.dagger", name = "hilt-android", version.ref = "hilt" }
room-runtime = { group = "androidx.room", name = "room-runtime", version.ref = "room" }
```

## Build Configuration

Use convention plugins in `build-logic/` for consistent configuration:
- `AndroidApplicationConventionPlugin` - App modules
- `AndroidLibraryConventionPlugin` - Library modules  
- `AndroidFeatureConventionPlugin` - Feature modules
- `AndroidComposeConventionPlugin` - Compose setup
- `AndroidHiltConventionPlugin` - Hilt setup

See [gradle-setup.md](references/gradle-setup.md) for complete build configuration.


---
Source attribution: dpconde
Original project: https://github.com/dpconde/claude-android-skill
License: MIT
License information: https://opensource.org/license/mit
Original upstream instructions; downloaded from Mega AI Hub.

## Upstream license notice

MIT License

Copyright (c) 2025 David Perez

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.



# Mega AI Hub resource metadata

Creator / publisher: dpconde
Original project: https://github.com/dpconde/claude-android-skill
Attribution basis: Original project named by vendored-folder README

Fields of work: Design, Development & Engineering, Product Management
Roles: Mobile Developer, Product Manager, UX Designer
Specialties: Backend, Mobile
Tools: Hilt, Jetpack Compose, Room
Country applicability: Country not specified
Classification basis: Source catalog labels
Instruction SHA-256: beb251137c931969bedc81a9748dcfd90381a3cf0e2f61ae15533e526cfb640a
Metadata reviewed: 2026-10-27
This metadata supersedes earlier Mega AI Hub catalog attribution. Original instruction and supporting files are preserved.