Performance Optimization in Jetpack Compose: Best Practices for Smooth UIs

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

Jetpack Compose makes building UIs easier with its declarative approach, but just like any UI framework, performance matters. Efficient rendering and avoiding unnecessary recompositions are critical for delivering smooth user experiences. In this article, we will explore key techniques and tools to optimize performance in Jetpack Compose applications.

1. Understanding Recomposition in Jetpack Compose

Recomposition is the process by which Jetpack Compose updates the UI when the state changes. It can be thought of as a redraw triggered by state changes. However, improper handling of state or excessive recompositions can lead to performance bottlenecks. Understanding how and when recomposition occurs is key to performance optimization.

• Avoid unnecessary recompositions: You should only recompose the parts of the UI that have actually changed.
• Recomposition does not mean re-rendering: Compose uses a smart diffing mechanism to only re-render changed elements, but inefficient state handling can still cause performance issues.

2. Minimizing Recomposition with remember

The remember function is one of the most effective ways to prevent unnecessary recompositions. It tells Compose to retain the value across recompositions.

a) Using remember in a List

@Composable
fun NumberList(numbers: List<Int>) {
    LazyColumn {
        items(numbers) { number ->
            NumberItem(number)
        }
    }
}

@Composable
fun NumberItem(number: Int) {
    var isSelected by remember { mutableStateOf(false) }

    Row(
        modifier = Modifier
            .fillMaxWidth()
            .clickable { isSelected = !isSelected }
            .background(if (isSelected) Color.Green else Color.Transparent)
    ) {
        Text("Number: $number")
    }
}        

By using remember in the NumberItem, we ensure that the selection state (isSelected) is maintained across recompositions without impacting the entire list.

3. Using key to Optimize Lazy Composables

Jetpack Compose provides LazyColumn and LazyRow for efficient list rendering. However, to ensure stable rendering when list items change (e.g., when adding/removing items), it’s crucial to provide a unique key for each item.

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

Providing a stable key helps Compose identify items correctly, reducing recompositions and improving performance when the list changes.

4. Optimize Composable Functions with Statelessness

A key principle for optimizing performance in Compose is keeping your Composables as stateless as possible. Stateless composables are easier to manage and less prone to unnecessary recompositions.

a) Example: Stateless Counter

@Composable
fun StatelessCounter(count: Int, onIncrement: () -> Unit) {
    Column {
        Text(text = "Count: $count")
        Button(onClick = onIncrement) {
            Text("Increment")
        }
    }
}        

Here, the StatelessCounter does not hold any state internally. It simply displays the count and provides a callback for incrementing it. This approach allows greater control over when and how recompositions occur.

5. Leverage DerivedStateOf for Efficient State Observations

The derivedStateOf function allows you to derive a value from other state objects, ensuring that recomposition only occurs when the derived value changes.

a) Example: Using derivedStateOf

@Composable
fun ExpensiveOperationDemo(numbers: List<Int>) {
    val evenNumbers = remember {
        derivedStateOf { numbers.filter { it % 2 == 0 } }
    }

    LazyColumn {
        items(evenNumbers.value) { number ->
            Text(text = "Even number: $number")
        }
    }
}        

In this example, Compose only recalculates evenNumbers when numbers changes, preventing unnecessary recompositions.

6. Efficient Handling of Animations

Animations can be resource-intensive if not handled correctly. Compose provides the animate*AsState functions, which are efficient for simple animations. For more complex animations, using remember with animation values can prevent recomposition of the entire screen.

a) Example: Efficient Animation with animateAsState

@Composable
fun ColorChangeBox() {
    var isSelected by remember { mutableStateOf(false) }
    val color by animateColorAsState(targetValue = if (isSelected) Color.Green else Color.Red)

    Box(
        modifier = Modifier
            .size(100.dp)
            .background(color)
            .clickable { isSelected = !isSelected }
    )
}        

Here, the background color of the box animates smoothly between red and green based on the state, but recomposition only occurs when necessary.

7. Using Snapshot for Efficient State Observations

Jetpack Compose introduces the concept of snapshots to manage state in a performant manner. When you observe state changes via mutableStateOf, Compose internally creates snapshots, which help optimize state management and recomposition.

8. Previewing UI Performance with Tools

Jetpack Compose provides performance measurement tools like Layout Inspector and CPU Profiler in Android Studio to help identify bottlenecks and optimize rendering.

a) Using the Layout Inspector

The Layout Inspector allows you to inspect the hierarchy of your Compose UI in real-time, helping identify unnecessary recompositions or inefficient layouts.

1. Run your app in Android Studio.
2. Go to View > Tool Windows > Layout Inspector.
3. Explore the composable tree to see how your UI is structured.

b) Using the CPU Profiler

The CPU Profiler is useful for monitoring the performance of your app's UI thread. It can help detect frame drops or identify functions that are taking too long to execute, which may cause jank in your app.

• Open CPU Profiler under View > Tool Windows > Profiler.
• Record a session while interacting with your app to identify slowdowns.

9. Lazy Composables: LazyColumn and LazyRow

When displaying large lists or grids of data, LazyColumn and LazyRow should be your go-to components for performance optimization. They render only the visible items and manage recycling of views automatically, significantly improving performance for large datasets.

a) Using LazyColumn for Long Lists

@Composable
fun NamesList(names: List<String>) {
    LazyColumn {
        items(names) { name ->
            Text(text = name)
        }
    }
}        

This ensures that only the visible names are rendered at any given time, reducing memory usage and CPU load.

10. Avoiding Expensive Operations in Composables

Avoid performing expensive computations or operations directly inside composables. If you need to perform such operations, offload them using side effects or background threads (with coroutines).

a) Example: Using LaunchedEffect for Background Work

@Composable
fun DataFetchingComposable() {
    var data by remember { mutableStateOf("Loading...") }

    LaunchedEffect(Unit) {
        data = fetchDataFromNetwork() // Simulate network call
    }

    Text(text = data)
}        

In this example, we use LaunchedEffect to fetch data in the background without blocking the UI thread.

11. Avoid Over-Nesting Composables

Although Compose allows deep nesting of Composables, over-nesting can negatively impact performance, particularly when dealing with large and complex UIs. Aim to keep the composable hierarchy as flat as possible.

12. Reusing and Sharing State Across Composables

Reusing state efficiently by passing it between Composables reduces the need for recompositions. This is particularly useful in larger apps where state can be lifted up and passed down as parameters.

13. Best Practices for Optimizing Performance

To summarize, here are some best practices for optimizing performance in Jetpack Compose:

• Use remember to avoid recomposition: Keep expensive operations out of the composable’s recomposition cycle by remembering values.
• Prefer stateless Composables: Keep your Composables stateless where possible and lift state up to manage it at a higher level.
• Use LazyColumn and LazyRow for large datasets: Optimize list rendering by using lazy components for efficient item recycling.
• Profile your app: Use tools like Layout Inspector and CPU Profiler to identify performance bottlenecks.
• Optimize animations: Use animate*AsState for simple animations and ensure they are scoped properly to avoid unnecessary recompositions.

14. Conclusion: Crafting Smooth UIs with Compose

Jetpack Compose offers powerful tools to help you optimize UI performance, from managing recompositions to leveraging lazy rendering. By following these best practices, you can ensure that your Compose app remains smooth and responsive, even as it scales in complexity.