android-jetpack-compose

# Android - Jetpack Compose

Modern declarative UI toolkit for building native Android interfaces.

## Key Concepts

### State Management

Compose provides several ways to manage state:

- **remember**: Survives recomposition
- **rememberSaveable**: Survives configuration changes
- **mutableStateOf**: Creates observable state
- **derivedStateOf**: Computed state that updates when dependencies change

```kotlin
@Composable
fun Counter() {
    var count by remember { mutableStateOf(0) }

    Column {
        Text("Count: $count")
        Button(onClick = { count++ }) {
            Text("Increment")
        }
    }
}

// With saveable for configuration changes
@Composable
fun SearchField() {
    var query by rememberSaveable { mutableStateOf("") }

    TextField(
        value = query,
        onValueChange = { query = it },
        placeholder = { Text("Search...") }
    )
}
```

### State Hoisting

Lift state up to make composables stateless and reusable:

```kotlin
// Stateless composable
@Composable
fun NameInput(
    name: String,
    onNameChange: (String) -> Unit,
    modifier: Modifier = Modifier
) {
    TextField(
        value = name,
        onValueChange = onNameChange,
        label = { Text("Name") },
        modifier = modifier
    )
}

// Stateful parent
@Composable
fun UserForm() {
    var name by remember { mutableStateOf("") }

    NameInput(
        name = name,
        onNameChange = { name = it }
    )
}
```

### ViewModel Integration

```kotlin
class UserViewModel : ViewModel() {
    private val _uiState = MutableStateFlow(UserUiState())
    val uiState: StateFlow<UserUiState> = _uiState.asStateFlow()

    fun updateName(name: String) {
        _uiState.update { it.copy(name = name) }
    }

    fun saveUser() {
        viewModelScope.launch {
            _uiState.update { it.copy(isLoading = true) }
            try {
                userRepository.save(_uiState.value.toUser())
                _uiState.update { it.copy(isLoading = false, isSaved