Minimizing Recompositions: Jetpack Compose Performance Guide

Jetpack Compose is a modern UI toolkit for building native Android apps using a declarative approach. One of its key features is automatic UI updates when the underlying data changes. However, excessive or unnecessary UI updates, known as recompositions, can lead to performance issues. This article explores various strategies for minimizing recompositions in Jetpack Compose, ensuring your app remains efficient and responsive.

Understanding Recomposition in Jetpack Compose

Recomposition is the process of re-executing composable functions when their input parameters change. Unlike traditional imperative UI programming, Compose automatically rebuilds parts of the UI that depend on changed data. While this simplifies UI development, uncontrolled recompositions can degrade performance, causing lag and jank.

Why Minimize Recompositions?

• Performance: Reducing unnecessary UI updates minimizes the amount of work the UI thread needs to perform.
• Efficiency: Less work means less CPU usage, resulting in better battery life for the user.
• Responsiveness: Fewer recompositions lead to a smoother and more responsive user interface.

Strategies for Minimizing Recompositions

Here are several strategies you can use to minimize recompositions in your Jetpack Compose applications:

1. Smart State Management with remember and mutableStateOf

The remember function in Compose allows you to store the state across recompositions. When combined with mutableStateOf, it ensures that only components that depend on the state are recomposed when the state changes.

import androidx.compose.runtime.*
import androidx.compose.material.Text
import androidx.compose.foundation.layout.Column
import androidx.compose.material.Button
import androidx.compose.ui.tooling.preview.Preview

@Composable
fun CounterExample() {
    var count by remember { mutableStateOf(0) }

    Column {
        Text("Count: $count")
        Button(onClick = { count++ }) {
            Text("Increment")
        }
    }
}

@Preview(showBackground = true)
@Composable
fun PreviewCounterExample() {
    CounterExample()
}

In this example, only the Text composable that displays the count and the Button need to recompose when the count changes.

2. Using rememberSaveable for Configuration Changes

For state that needs to survive configuration changes (like screen rotations), use rememberSaveable. It saves the state to Bundle during Activity.onSaveInstanceState().

import androidx.compose.runtime.*
import androidx.compose.material.Text
import androidx.compose.foundation.layout.Column
import androidx.compose.material.Button
import androidx.compose.runtime.saveable.rememberSaveable
import androidx.compose.ui.tooling.preview.Preview

@Composable
fun SaveableCounterExample() {
    var count by rememberSaveable { mutableStateOf(0) }

    Column {
        Text("Count: $count")
        Button(onClick = { count++ }) {
            Text("Increment")
        }
    }
}

@Preview(showBackground = true)
@Composable
fun PreviewSaveableCounterExample() {
    SaveableCounterExample()
}

The state is preserved across configuration changes, preventing unnecessary resets and recompositions.

3. Stable Data Types and Keys

Compose uses referential equality checks to determine if recomposition is needed. Therefore, using immutable data types and keys can prevent unnecessary recompositions. Ensure your data classes are stable by using val for properties and avoiding mutable collections.

import androidx.compose.runtime.Immutable

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

@Composable
fun UserProfile(user: User) {
    Text("User ID: ${user.id}, Name: ${user.name}")
}

If User is immutable, Compose can efficiently determine if it has changed.

4. Using derivedStateOf to Optimize State Reads

derivedStateOf lets you create a derived state that only updates when the underlying state changes, avoiding unnecessary recompositions.

import androidx.compose.runtime.*
import androidx.compose.material.Text
import androidx.compose.ui.tooling.preview.Preview

@Composable
fun DisplayName(firstName: String, lastName: String) {
    val fullName by remember {
        derivedStateOf { "$firstName $lastName" }
    }
    Text("Full Name: $fullName")
}

@Preview(showBackground = true)
@Composable
fun PreviewDisplayName() {
    DisplayName("John", "Doe")
}

fullName only updates when either firstName or lastName changes.

5. Skipping Unnecessary Compositions with rememberUpdatedState

rememberUpdatedState can be useful when a frequently changing state is passed to an event handler or a callback function. It ensures the callback always has the latest value without causing recomposition.

import androidx.compose.runtime.*
import androidx.compose.material.Button
import androidx.compose.material.Text
import androidx.compose.ui.tooling.preview.Preview

@Composable
fun DelayedMessage(message: String, onTimeout: () -> Unit) {
    val updatedOnTimeout by rememberUpdatedState(newValue = onTimeout)

    LaunchedEffect(key1 = Unit) {
        kotlinx.coroutines.delay(3000) // Simulate a delay
        updatedOnTimeout()
    }
    Text("Displaying message: $message")
}

@Preview(showBackground = true)
@Composable
fun PreviewDelayedMessage() {
    var count by remember { mutableStateOf(0) }

    DelayedMessage(message = "Message $count", onTimeout = { count++ })
}

The onTimeout callback always has the latest value of count without the DelayedMessage composable recomposing when count changes.

6. Leveraging CompositionLocal

CompositionLocal allows you to pass data implicitly down the composable tree. If the data rarely changes, using CompositionLocal can avoid unnecessary recompositions in unrelated parts of the UI.

import androidx.compose.runtime.*
import androidx.compose.material.Text
import androidx.compose.ui.platform.LocalContext
import androidx.compose.ui.tooling.preview.Preview
import androidx.compose.ui.unit.dp
import androidx.compose.foundation.layout.PaddingValues

val LocalPadding = compositionLocalOf { PaddingValues(0.dp) }

@Composable
fun MyComposable() {
    CompositionLocalProvider(LocalPadding provides PaddingValues(16.dp)) {
        ChildComposable()
    }
}

@Composable
fun ChildComposable() {
    val padding = LocalPadding.current
    Text("With Padding", modifier = androidx.compose.ui.Modifier.padding(padding))
}

@Preview(showBackground = true)
@Composable
fun PreviewMyComposable() {
    MyComposable()
}

In this example, the padding is passed implicitly to the ChildComposable, avoiding the need to explicitly pass it as a parameter, potentially reducing recompositions.

7. Inspecting Recompositions with Layout Inspector

Android Studio’s Layout Inspector provides tools to inspect and diagnose recompositions. You can highlight recomposing components and analyze the frequency of recompositions, helping you identify performance bottlenecks.

Conclusion

Minimizing recompositions is crucial for building performant and efficient Jetpack Compose applications. By employing strategies such as smart state management with remember and mutableStateOf, using stable data types, optimizing state reads with derivedStateOf, leveraging CompositionLocal, and inspecting recompositions with the Layout Inspector, you can ensure your app delivers a smooth and responsive user experience.