android-kotlin-coroutines

# Android - Kotlin Coroutines

Asynchronous programming patterns using Kotlin coroutines and Flow in Android.

## Key Concepts

### Coroutine Basics

```kotlin
// Launching coroutines
class UserViewModel : ViewModel() {

    fun loadUser(id: String) {
        // viewModelScope is automatically cancelled when ViewModel is cleared
        viewModelScope.launch {
            try {
                val user = userRepository.getUser(id)
                _uiState.value = UiState.Success(user)
            } catch (e: Exception) {
                _uiState.value = UiState.Error(e.message)
            }
        }
    }

    // For operations that return a value
    fun fetchUserAsync(id: String): Deferred<User> {
        return viewModelScope.async {
            userRepository.getUser(id)
        }
    }
}

// Suspend functions
suspend fun fetchUserFromNetwork(id: String): User {
    return withContext(Dispatchers.IO) {
        api.getUser(id)
    }
}
```

### Dispatchers

```kotlin
// Main - UI operations
withContext(Dispatchers.Main) {
    textView.text = "Updated"
}

// IO - Network, database, file operations
withContext(Dispatchers.IO) {
    val data = api.fetchData()
    database.save(data)
}

// Default - CPU-intensive work
withContext(Dispatchers.Default) {
    val result = expensiveComputation(data)
}

// Custom dispatcher for limited parallelism
val limitedDispatcher = Dispatchers.IO.limitedParallelism(4)
```

### Flow Basics

```kotlin
// Creating flows
fun getUsers(): Flow<List<User>> = flow {
    while (true) {
        val users = api.getUsers()
        emit(users)
        delay(30_000) // Poll every 30 seconds
    }
}

// Flow from Room
@Dao
interface UserDao {
    @Query("SELECT * FROM users")
    fun getAllUsers(): Flow<List<UserEntity>>
}

// Collecting flows
viewModelScope.launch {
    userRepository.getUsers()
        .catch { e -> _uiState.value = UiState.Error(e) }
        .collect { users ->
            _uiState.value = UiState.Success(users)
        }
}
``