Jetpack Compose has revolutionized Android UI development with its declarative approach. However, managing state, especially at a global level, can become complex in larger applications. This article explores effective strategies for handling global state in Compose, ensuring maintainability and scalability.  

Compose encourages unidirectional data flow. State changes trigger recompositions, updating the UI. While remember effectively manages state within a composable's scope, it's insufficient for sharing state across the entire application. This is where global state management solutions come into play.  

1. ViewModel for UI-Related State:

ViewModels, part of Android Architecture Components, are ideal for managing UI-related state that survives configuration changes. They act as a bridge between the UI and the data layer. In Compose, we can easily access ViewModels using viewModel() from the androidx.lifecycle:lifecycle-viewmodel-compose dependency.  

Kotlin

@Composable
fun MyScreen(viewModel: MyViewModel = viewModel()) {
    val uiState by viewModel.uiState.collectAsState()

    // ... use uiState to update the UI
}

class MyViewModel : ViewModel() {
    private val _uiState = MutableStateFlow(UiState())
    val uiState: StateFlow<UiState> = _uiState.asStateFlow()

    // ... functions to update _uiState
}

data class UiState(val isLoading: Boolean = false, val data: String? = null)

Here, collectAsState() converts the StateFlow from the ViewModel into a Compose State, triggering recompositions when the uiState changes. This pattern effectively manages state related to a specific screen or feature.

2. Dependency Injection for Shared Dependencies:

For state that needs to be shared across multiple features or modules, dependency injection (DI) frameworks like Hilt or Koin are crucial. They provide a centralized way to manage and provide instances of shared dependencies, including repositories, data sources, and other state holders.

Kotlin

@AndroidEntryPoint
class MyApplication : Application() { /* ... */ }

@Module
@InstallIn(SingletonComponent::class)
object AppModule {
    @Provides
    @Singleton
    fun provideDataRepository(): DataRepository = DataRepositoryImpl()
}

@AndroidEntryPoint
class MyActivity : ComponentActivity() {
    private val repository: DataRepository by inject() // Using Koin example

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {
            MyScreen()
        }
    }
}

By injecting the DataRepository, any composable within the application can access the same instance and its state.

3. State Holders for Complex Global State:

For more complex global state that isn't directly tied to a specific screen or ViewModel, dedicated state holder classes are beneficial. These classes encapsulate the state and the logic to modify it. They can be provided via DI, making them accessible throughout the application.  

Kotlin

class AppStateHolder {
    private val _user = MutableStateFlow<User?>(null)
    val user: StateFlow<User?> = _user.asStateFlow()

    fun login(user: User) {
        _user.value = user
    }

    fun logout() {
        _user.value = null
    }
}

This AppStateHolder manages the user's login state. By providing it as a singleton via DI, any part of the application can observe changes to the user and react accordingly.

4. Accompanist Navigation for Navigation State:

If your global state is closely tied to navigation, consider using Accompanist Navigation. It provides a more robust and Compose-friendly way to handle navigation, including managing state related to destinations.  

Conclusion:

Effectively managing global state is essential for building robust and maintainable Compose applications. By combining ViewModels for UI-related state, dependency injection for shared dependencies, dedicated state holders for complex global state, and tools like Accompanist Navigation, you can create a well-structured application that handles state changes efficiently and predictably. Choosing the right approach depends on the specific needs of your application, but these strategies provide a solid foundation for mastering global state management in Jetpack Compose.