android-architecture

# Android - Architecture

Modern Android architecture patterns following Google's recommended practices.

## Key Concepts

### MVVM Architecture

Model-View-ViewModel separates UI from business logic:

```kotlin
// UI State
data class UserUiState(
    val user: User? = null,
    val isLoading: Boolean = false,
    val error: String? = null
)

// ViewModel
class UserViewModel(
    private val userRepository: UserRepository
) : ViewModel() {

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

    fun loadUser(userId: String) {
        viewModelScope.launch {
            _uiState.update { it.copy(isLoading = true, error = null) }

            userRepository.getUser(userId)
                .onSuccess { user ->
                    _uiState.update { it.copy(user = user, isLoading = false) }
                }
                .onFailure { error ->
                    _uiState.update { it.copy(error = error.message, isLoading = false) }
                }
        }
    }
}

// Composable
@Composable
fun UserScreen(viewModel: UserViewModel = hiltViewModel()) {
    val uiState by viewModel.uiState.collectAsStateWithLifecycle()

    when {
        uiState.isLoading -> LoadingIndicator()
        uiState.error != null -> ErrorMessage(uiState.error!!)
        uiState.user != null -> UserContent(uiState.user!!)
    }
}
```

### Clean Architecture Layers

```
app/
├── data/
│   ├── local/           # Room database, DataStore
│   │   ├── dao/
│   │   └── entities/
│   ├── remote/          # Retrofit, network
│   │   ├── api/
│   │   └── dto/
│   └── repository/      # Repository implementations
├── domain/
│   ├── model/           # Domain models
│   ├── repository/      # Repository interfaces
│   └── usecase/         # Business logic
└── presentation/
    ├── ui/              # Composables
    └── viewmodel/       # ViewModels
```

### Repository Pattern

```kotlin
// Domain layer - interface
interface UserRep