Mastering Recomposition in Jetpack Compose: Strategies for Optimal Performance

Jetpack Compose offers a declarative approach to building UI on Android, with the capability to automatically re-render (recomposition) when the state changes. However, not all recompositions are necessary or optimal. Excessive or frequent recompositions can lead to performance degradation, especially in complex applications.

This article will discuss how to detect unwanted recompositions and provide tips for optimizing them in Jetpack Compose.

What Is Recomposition?

Recomposition is the process by which Jetpack Compose re-renders the UI when there is a change in the state used by a composable. This process is automatic, allowing for reactive UI development. However, if not managed properly, unnecessary recomposition can lead to performance issues such as lagging and high memory usage.

Why Can Excessive Recomposition Be a Problem?

Excessive recomposition, especially in complex composables or large lists, can adversely affect application performance. Common symptoms of this issue include:

• UI Lag: Users experience delays when interacting with the app.
• High Memory Usage: The app becomes slow or even crashes due to inefficient memory usage.
• Frame Drops: Animations and transitions do not run smoothly.

How to Detect Recomposition

Using Compose Layout Inspector

Compose Layout Inspector in Android Studio is a valuable tool for analyzing how composables are rendered and recomposed. Here are the steps to use this tool:

1. Open Layout Inspector:

• Run your app on an emulator or physical device.
• In Running Devices window, click icon marked below.

2. Select Composable to Inspect:

• The Layout Inspector will display a hierarchy of composables from the running UI.
• Select the composable you want to analyze to view information about recomposition.

3. Observe Recomposition:

• Layout Inspector allows you to see which UI elements are being recomposed.
• Pay attention to parts of the UI that are being recomposed excessively or unexpectedly.

In the example above, the Text has been recomposed 7 times after pressing FloatingActionButton 7 times.

How to Optimize Recomposition

Once you have identified areas with excessive recomposition, the next step is to optimize them. Here are some tips to reduce recomposition frequency without affecting the app’s functionality.

1. Use remember to Store Local State

Using remember to store state that does not need recomposition is a straightforward way to reduce recomposition frequency. With remember, the value is computed only once and stored as long as the composable's lifecycle does not change.

@Composable
fun Greeting(name: String) {
    val greeting = remember { "Hello, $name!" }

    Text(text = greeting)
}

Example of Code Causing Excessive Recomposition:

@Composable
fun Greeting(name: String) {
    Text(text = "Hello, $name!")

    // This calculation happens every time the UI is recomposed.
    val currentTime = System.currentTimeMillis()

    Text(text = "Current time: $currentTime")
}

In the example above, currentTime is recalculated every time the composable is recomposed, even though its result might not change. This leads to excessive recomposition.

2. Use key in LazyColumn for Dynamic Lists

When working with dynamic lists, such as user lists or product items, ensure you use key in LazyColumn. This helps Compose track elements more efficiently, so only elements that truly change will be recomposed.

@Composable
fun ItemList(items: List<Item>) {
    LazyColumn {
        items(items, key = { it.id }) { item ->
            Text(text = item.name)
        }
    }
}

Example of Code Causing Excessive Recomposition:

@Composable
fun ItemList(items: List<Item>) {
    LazyColumn {
        items(items) { item ->
            Text(text = item.name)
        }
    }
}

In the example above, without key, Jetpack Compose may have trouble tracking specific changes in the list, causing the entire list to be recomposed even for minor changes, potentially degrading performance.

3. Use derivedStateOf to Manage Limited State Changes

When you have state calculated from other state, use derivedStateOf. This ensures that the computed result only changes when the underlying state changes, not on every recomposition.

@Composable
fun TemperatureDisplay(celsius: Float) {
    val fahrenheit by remember {
        derivedStateOf { celsius * 9/5 + 32 }
    }

    Text(text = "$Fahrenheit °F")
}

With derivedStateOf, you ensure that temperature conversion is calculated only when the celsius value changes, not every time the UI is recomposed.

Example of Code Causing Excessive Recomposition:

@Composable
fun TemperatureDisplay(celsius: Float) {
    // This calculation happens every time the composable is recomposed
    val fahrenheit = celsius * 9/5 + 32

    Text(text = "$Fahrenheit °F")
}

In this case, fahrenheit is recalculated every time TemperatureDisplay is recomposed, which can lead to performance degradation, especially if this composable is called repeatedly.

4. Use Immutable for Unchanging Data Collections

If you are working with data that does not change (immutable), inform Compose that the data will not change using the @Immutable annotation. This prevents Compose from performing unnecessary recompositions on data that should not change.

@Immutable
data class User(
  val id: Int, 
  val name: String, 
  val email: String
)

By marking data as immutable, Compose can optimize state management and avoid unnecessary rendering.

5. Break Composables into Smaller Parts

If a large composable is experiencing excessive recomposition, try breaking it into smaller, focused composables. This way, only small parts of the UI will be recomposed when state changes, not the entire UI.

@Composable
fun UserProfile(user: User) {
    Column {
        UserName(user.name)
        UserEmail(user.email)
    }
}

@Composable
fun UserName(name: String) {
    Text(text = name)
}

@Composable
fun UserEmail(email: String) {
    Text(text = email)
}

Example of Code Causing Excessive Recomposition:

@Composable
fun UserProfile(user: User) {
    Column {
        Text(text = user.name)
        Text(text = user.email)
        // Button that also gets recomposed even if not needed
        Button(onClick = {
            println("Button clicked!")
        }) {
            Text("Click Me")
        }
    }
}

In this example, the Button will be recomposed every time UserProfile is recomposed, even though there are no state changes affecting the Button. This causes excessive recomposition in parts of the UI that do not need to be re-rendered.

Conclusion

Managing recomposition wisely in Jetpack Compose is crucial for maintaining optimal application performance. By using Compose Layout Inspector in Android Studio to detect unwanted recompositions and applying optimization techniques such as remember, derivedStateOf, and breaking composables into smaller parts, you can ensure your Compose applications run smoothly.

By implementing these techniques, you’ll be able to tackle recomposition challenges and build efficient, responsive, and enjoyable applications.

#JetpackCompose #AndroidDevelopment #ComposeOptimization #Recomposition #MobilePerformance