Optimizing Recomposition in Jetpack Compose: How to Prevent Unnecessary UI Updates

Jetpack Compose introduces a declarative and reactive UI model, allowing Android developers to build dynamic UIs with ease. However, with this reactive paradigm comes the concept of recomposition — the process by which Compose redraws parts of the UI when the underlying state changes.

While recompositions are highly efficient, unnecessary recompositions can still impact performance. This article will explore the best techniques to optimize your Compose code and prevent unnecessary recompositions.

Understanding Recomposition in Jetpack Compose

Recomposition is Compose’s mechanism for updating the UI when state changes. When a state value changes, Compose identifies the parts of the UI that depend on that state and re-evaluates them. However, excessive recomposition can lead to performance issues.

Why Does Recomposition Happen?

Compose recomposes when:

• State used by a Composable changes.
• A parent Composable triggers recomposition for its child Composables.
• New instances of Composables are created with different parameters.

Our goal is to ensure that recompositions only happen when absolutely necessary. Here’s how we can achieve that.

1. Using remember for State Preservation

Compose provides the remember function to store values across recompositions. This is essential for preventing expensive recalculations when the value doesn’t need to be recalculated on every recomposition.

Example:

@Composable
fun MyComposable() {
    val expensiveCalculation = remember {
        // Expensive operation that should not be recalculated on every recomposition
        performExpensiveCalculation()
    }

    Text("Result: $expensiveCalculation")
}

Without remember, performExpensiveCalculation() would run on every recomposition. By wrapping it with remember, the result is cached, and the expensive calculation only happens once, unless the Composable is recreated.

2. Storing Mutable State with remember and mutableStateOf

When you need mutable state that persists across recompositions, pair remember with mutableStateOf. This combination ensures that the state persists across recompositions and the UI only updates when necessary.

Example:

@Composable
fun MyCounter() {
    val counter = remember { mutableStateOf(0) }

    Button(onClick = { counter.value++ }) {
        Text("Count: ${counter.value}")
    }
}

This prevents the counter from being reset on every recomposition and ensures that only the Text displaying the count is updated when the counter changes.

3. Using key for Scoped remember

Sometimes you want to recompute a value only when a specific parameter changes. You can achieve this by scoping remember using the key function. This ensures that a cached value is recomputed only when the key changes.

Example:

@Composable
fun MyScreen(id: Int) {
    val result = remember(id) {
        // Only recomputes when `id` changes
        performExpensiveCalculationForId(id)
    }

    Text("Result for ID: $id is $result")
}

In this example, performExpensiveCalculationForId() is only invoked when id changes, avoiding unnecessary recompositions when other state values change.

4. Handling Side Effects with LaunchedEffect

When dealing with side effects — such as network requests or other non-UI operations — you want to make sure these side effects are only triggered when necessary. Compose provides LaunchedEffect for this purpose.

Example:

@Composable
fun MyComposable(id: Int) {
    LaunchedEffect(id) {
        // Only triggered when `id` changes
        performNetworkCall(id)
    }
}

In this example, the network call is only triggered when the id changes, ensuring that this side effect is managed efficiently and doesn’t run unnecessarily on every recomposition.

5. Using derivedStateOf for Dependent State

If you have state that is derived from other state values, use derivedStateOf to optimize when this derived state is recalculated. derivedStateOf ensures that the derived value is only recomputed when its source state changes.

Example:

@Composable
fun MyDerivedStateExample() {
    val list = remember { listOf(1, 2, 3, 4) }
    val sum = remember { derivedStateOf { list.sum() } }

    Text("Sum of list: ${sum.value}")
}

In this example, the sum is only recalculated when the list changes. If other parts of the Composable trigger a recomposition, the sum remains unchanged unless its dependencies change.

6. Leveraging Stable Data Structures

Compose optimizes recompositions based on the stability of the data being passed to Composables. If your data structures are immutable or stable, Compose can better understand when things have actually changed, avoiding unnecessary recompositions.

For instance, using Kotlin’s data classes provides stable data structures:

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

@Composable
fun UserCard(user: User) {
    Text("Name: ${user.name}, Age: ${user.age}")
}

Since data classes implement proper equals and hashCode methods, Compose can determine whether the User object has actually changed, and will only trigger recomposition when necessary.

7. Breaking Down Large Composables

Breaking large Composables into smaller, more focused ones helps reduce unnecessary recompositions. By splitting up the UI, Compose can recompose only the parts of the UI that depend on state changes, rather than recomposing the entire screen.

Example:

@Composable
fun MainScreen(user: User) {
    Column {
        UserCard(user)
        StaticContent()
    }
}

@Composable
fun UserCard(user: User) {
    Text("User: ${user.name}")
}

@Composable
fun StaticContent() {
    Text("Some static content")
}

In this case, if user changes, only the UserCard is recomposed, while the StaticContent remains unchanged. This keeps recomposition efficient and focused only on the parts of the UI that need updating.

Conclusion: Efficiently Managing Recomposition in Compose

Recomposition is one of the core mechanisms that powers the reactive nature of Jetpack Compose. However, unnecessary recompositions can lead to performance issues, especially in complex UIs. By using remember, LaunchedEffect, derivedStateOf, and stable data structures, you can optimize your Compose code to recompose only when necessary.

Understanding how Compose manages recomposition and using these techniques will help you write more efficient and responsive UIs, ensuring a smooth user experience.

Happy composing! 🎨

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