Optimizing Recomposition in Jetpack Compose for Performance

Jetpack Compose, Google’s modern toolkit for building native Android UIs, simplifies UI development by adopting a declarative approach. However, as Compose relies heavily on recomposition to update the UI, understanding and optimizing recomposition becomes crucial for achieving high performance in your apps.

This blog dives into the nuances of recomposition, explores best practices for minimizing unnecessary recompositions, and provides actionable tips to build efficient, performant UIs with Jetpack Compose.

Understanding Recomposition in Jetpack Compose

Recomposition is the process by which Jetpack Compose updates the UI in response to changes in the state. When a piece of state changes, Compose recalculates the parts of the UI tree that depend on that state. While this ensures a responsive UI, excessive or unnecessary recompositions can degrade performance.

How Recomposition Works

  1. State Changes: Compose observes state objects (e.g., State, MutableState, remember, or derivedStateOf). When a state changes, it triggers recomposition.

  2. Scoped Recomposition: Compose intelligently scopes recomposition to the smallest necessary part of the UI tree.

  3. Skipping Recomposition: Compose skips recomposition for unchanged state or when composable functions produce the same results.

Key Terms to Know

  • Composable Functions: Functions annotated with @Composable, defining the UI structure.

  • State Hoisting: A pattern where state is passed down and events are passed up, allowing better control over recomposition.

  • Snapshot System: Compose's internal mechanism for tracking state changes efficiently.

Best Practices to Optimize Recomposition

1. Use State Efficiently

Efficient state management is at the heart of recomposition optimization.

Avoid Overloading State

  • Keep state granular. A single large state object can lead to unnecessary recompositions of unrelated parts of the UI.

  • Use derivedStateOf to derive values instead of recalculating them in every recomposition.

Leverage Immutable State

  • Use immutable data classes for state whenever possible. Immutable objects reduce the chances of unintended state mutations that can trigger recompositions.

val count by remember { mutableStateOf(0) }
val derivedText = remember(count) { "Count is $count" }

2. Understand and Leverage remember and rememberUpdatedState

  • Use remember to store values across recompositions without reinitializing them.

  • Use rememberUpdatedState for lambdas or state values that must always use the latest data.

Example: Avoiding Unnecessary Initialization

@Composable
fun Timer(onTick: (Int) -> Unit) {
    val currentOnTick by rememberUpdatedState(onTick)

    LaunchedEffect(Unit) {
        var count = 0
        while (true) {
            delay(1000)
            currentOnTick(count++)
        }
    }
}

3. Use Keys for Efficient List Updates

When dealing with dynamic lists, ensure Compose can identify which items have changed by using unique keys.

Example: Using Keys in LazyColumn

LazyColumn {
    items(items, key = { it.id }) { item ->
        Text(item.name)
    }
}

This approach prevents unnecessary recompositions of unchanged list items.

4. Leverage derivedStateOf for Computed Values

If you’re computing a value derived from state, use derivedStateOf to recompute the value only when necessary.

Example: Efficient Computation

val sortedItems by remember(items) {
    derivedStateOf { items.sortedBy { it.name } }
}

5. Minimize Recomposition Scope

Keep composable functions as small and focused as possible. This ensures recompositions are scoped to smaller UI segments, minimizing their impact.

Example: Splitting UI Logic

@Composable
fun UserList(users: List<User>) {
    Column {
        users.forEach { user ->
            UserRow(user)
        }
    }
}

@Composable
fun UserRow(user: User) {
    Text(user.name)
}

In this example, recomposing a single UserRow doesn’t recompose the entire list.

6. Avoid Heavy Computation in Composables

  • Offload expensive operations to background threads using LaunchedEffect or CoroutineScope.

  • Cache results with remember for reuse.

Example: Caching Results

val processedData by remember(rawData) {
    derivedStateOf { processData(rawData) }
}

7. Use Stable Data Structures

Mark custom classes as @Stable to let Compose know the data doesn’t change unexpectedly.

Example: Using @Stable

@Stable
data class User(val name: String, val age: Int)

Debugging and Measuring Recomposition

Debugging Tools

  1. Debug Recompose Counts: Use the Recompose composable in the androidx.compose.runtime.tooling package to count recompositions.

Example: Logging Recomposition

@Composable
fun DebuggableComposable() {
    val count = remember { mutableStateOf(0) }
    Recompose { count.value++ }
    Text("Recompose count: ${count.value}")
}

  1. Layout Inspector: Analyze composable hierarchy and recompositions.

  2. Systrace: Capture detailed performance data.

Measuring Performance

  • Profile your app using Android Studio’s Profiler.

  • Look for excessive recompositions or frame drops.

Advanced Tips for Performance Optimization

Avoid Unnecessary State Observations

Ensure composables observe only the necessary parts of the state. Break down state objects into smaller pieces when possible.

Use Composition Locals Wisely

Composition locals can share data across a composition tree but use them sparingly to avoid unnecessary recompositions.

Example: Using CompositionLocal

val LocalUser = compositionLocalOf<User> { error("No user provided") }

@Composable
fun MyApp() {
    CompositionLocalProvider(LocalUser provides currentUser) {
        UserProfile()
    }
}

Preload Heavy UI Elements

Preload or cache heavy UI components to reduce runtime overhead.

Example: Preloading Images

val imageBitmap = remember { mutableStateOf<ImageBitmap?>(null) }
LaunchedEffect(Unit) {
    imageBitmap.value = loadImage() // Load in the background
}
Image(bitmap = imageBitmap.value!!, contentDescription = null)

Conclusion

Optimizing recomposition in Jetpack Compose is essential for building performant and responsive apps. By understanding how recomposition works and applying these best practices, you can ensure your app remains snappy and resource-efficient, even with complex UI interactions.

Start by analyzing recomposition patterns in your app, applying scoped recomposition, and leveraging tools like remember, derivedStateOf, and Layout Inspector. With these strategies, you’ll be well-equipped to tackle performance challenges and unlock the full potential of Jetpack Compose.