Handling Side Effects in Jetpack Compose: A Deep Dive into LaunchedEffect, SideEffect, and DisposableEffect

Part of the series "Android Development Series by Mircea Ioan Soit"

In Jetpack Compose, side effects are operations that need to interact with the external world or manage asynchronous tasks, like fetching data from a network, performing IO operations, or reacting to lifecycle changes. Compose provides several tools to handle these side effects efficiently: LaunchedEffect, SideEffect, and DisposableEffect. In this article, we'll break down each of these APIs and how to use them effectively.

1. What Are Side Effects in Compose?

Side effects in Jetpack Compose are operations that go beyond the realm of pure UI rendering. They typically include:

• Network requests or other IO tasks
• Lifecycle-aware actions (e.g., subscribing to data sources)
• State that must be persisted across re-compositions
• Triggers that must be executed when certain state changes occur

Compose, being a declarative framework, handles recompositions automatically. But when dealing with side effects, developers need to be careful to avoid causing unwanted side effects during recomposition. Jetpack Compose provides specific APIs to manage them efficiently.

2. LaunchedEffect: Managing Asynchronous Work

LaunchedEffect is the most commonly used side-effect handler in Compose. It allows you to run a suspend function when a given key changes or when the Composable is first composed. It’s ideal for executing asynchronous tasks such as fetching data from a network or performing database operations.

a) Basic Example: Fetching Data

@Composable
fun FetchDataComposable(userId: String) {
    var userData by remember { mutableStateOf("Loading...") }

    // LaunchedEffect runs once when `userId` changes
    LaunchedEffect(userId) {
        userData = fetchUserData(userId) // Assume fetchUserData is a suspend function
    }

    Text(text = userData)
}        

In this example, the LaunchedEffect block runs whenever the userId parameter changes. The userData state is updated with the result of the network call, and the UI is automatically recomposed to display the updated information.

b) Ensuring One-Time Execution

If you want to execute an effect only once (e.g., on the initial composition), use LaunchedEffect(Unit):

LaunchedEffect(Unit) {
    // This block will only run once
    performInitialSetup()
}        

3. SideEffect: Synchronizing with External Systems

The SideEffect API is used when you need to execute non-suspend code that affects external systems but must be guaranteed to run after every successful recomposition. It’s useful for updating external UI systems like the Android view hierarchy or interfacing with third-party libraries.

a) Example: Updating Analytics

@Composable
fun AnalyticsComposable(screenName: String) {
    SideEffect {
        // SideEffect runs after every successful recomposition
        sendAnalyticsEvent("Screen Viewed: $screenName")
    }

    Text(text = "Current screen: $screenName")
}        

In this case, SideEffect ensures that the analytics event is sent every time the composable recomposes, keeping external systems in sync with the UI state.

4. DisposableEffect: Cleanup When Composables Exit

DisposableEffect is designed for side effects that need a cleanup action when a composable leaves the composition. This is useful for scenarios like setting up listeners, subscriptions, or other resources that must be disposed of when no longer needed.

a) Example: Setting Up and Cleaning Up a Listener

@Composable
fun SensorListener(sensorManager: SensorManager) {
    DisposableEffect(Unit) {
        val listener = object : SensorEventListener {
            override fun onSensorChanged(event: SensorEvent) { /* handle event */ }
            override fun onAccuracyChanged(sensor: Sensor, accuracy: Int) { /* handle accuracy change */ }
        }
        sensorManager.registerListener(listener, sensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER), SensorManager.SENSOR_DELAY_NORMAL)

        onDispose {
            // Clean up the listener when the Composable leaves the composition
            sensorManager.unregisterListener(listener)
        }
    }

    Text("Sensor is active")
}        

In this example, the DisposableEffect sets up a SensorEventListener when the Composable enters the composition. The onDispose block ensures that the listener is unregistered when the Composable is removed from the UI, preventing memory leaks or unwanted behaviors.

5. Remember CoroutineScope with rememberCoroutineScope

Compose also provides rememberCoroutineScope, which allows you to create and manage coroutines in a more flexible way, particularly when dealing with actions that should be triggered on user events rather than inside recomposition.

a) Example: Triggering Coroutines from User Events

@Composable
fun UserActionButton() {
    val coroutineScope = rememberCoroutineScope()

    Button(onClick = {
        coroutineScope.launch {
            // Perform some background task
            performBackgroundTask()
        }
    }) {
        Text("Start Task")
    }
}        

rememberCoroutineScope gives you a coroutine scope that’s tied to the lifecycle of the composable, ensuring the coroutine is automatically canceled if the composable leaves the composition.

6. Using produceState for Asynchronous State

produceState is a helper that can be used to convert a suspend function into stateful data that can be observed in a Composable. It’s perfect for managing state derived from an asynchronous source.

a) Example: Loading Data Asynchronously

@Composable
fun AsyncDataLoader(userId: String) {
    val userData = produceState(initialValue = "Loading...", userId) {
        value = fetchUserData(userId) // Update the state with the result of the suspend function
    }

    Text(text = userData.value)
}        

produceState is a specialized API that handles the lifecycle of suspend functions and provides reactive state updates to the UI without manual intervention.

7. Handling Lifecycle Events with LaunchedEffect

LaunchedEffect can also be used to handle lifecycle events in Compose. For instance, you can observe lifecycle events to trigger actions such as pausing or resuming a task.

a) Example: Reacting to Lifecycle Changes

@Composable
fun LifecycleObserverExample() {
    val lifecycleOwner = LocalLifecycleOwner.current

    LaunchedEffect(lifecycleOwner) {
        val observer = LifecycleEventObserver { _, event ->
            when (event) {
                Lifecycle.Event.ON_PAUSE -> println("App paused")
                Lifecycle.Event.ON_RESUME -> println("App resumed")
                else -> Unit
            }
        }

        lifecycleOwner.lifecycle.addObserver(observer)

        onDispose {
            lifecycleOwner.lifecycle.removeObserver(observer)
        }
    }

    Text(text = "Observing lifecycle events")
}        

In this example, we use LaunchedEffect to observe the lifecycle events of the current composable. When the lifecycle changes, we can react to it, and we ensure proper cleanup using onDispose.

8. Best Practices for Handling Side Effects in Compose

To effectively manage side effects in Jetpack Compose, consider the following best practices:

• Use LaunchedEffect for async tasks: Run suspend functions tied to state changes or when a Composable enters the composition.
• Use SideEffect for non-suspend code: Synchronize external UI systems or other side effects that don’t require cleanup.
• Use DisposableEffect for cleanup: Manage resources like listeners or subscriptions that need cleanup when the Composable is removed from the composition.
• Remember coroutines for user-triggered events: Use rememberCoroutineScope to launch coroutines based on user interactions or events.
• Ensure proper disposal: Always use onDispose in DisposableEffect to clean up resources to prevent memory leaks.

9. Conclusion: Mastering Side Effects in Compose

Jetpack Compose provides powerful tools for handling side effects in a declarative UI framework. By using LaunchedEffect, SideEffect, and DisposableEffect, you can efficiently manage asynchronous tasks, external dependencies, and lifecycle-aware actions while keeping your UI responsive and performant.