Avoiding Expensive Calculations in Jetpack Compose: Performance Optimization

Jetpack Compose simplifies UI development in Android with its declarative approach. However, the ease of recomposition can sometimes lead to unintended performance issues if not managed properly. One common problem is performing expensive calculations directly within composable functions. These calculations can trigger frequent recompositions, leading to a laggy and unresponsive UI.

Understanding the Problem

Recomposition is the process of re-executing composable functions when their inputs change. While efficient, frequent recompositions can become costly if they involve expensive operations like complex mathematical calculations, large data processing, or heavy I/O tasks. To maintain optimal performance, it’s essential to identify and mitigate these expensive calculations.

Why Expensive Calculations Cause Issues

• Increased CPU Usage: Complex computations consume CPU resources, impacting overall app performance.
• UI Jank: Frequent recompositions can cause frame drops, resulting in UI jank and a poor user experience.
• Battery Drain: Constant calculations lead to increased battery consumption, which can affect user satisfaction.

Techniques to Avoid Expensive Calculations

Here are several techniques to prevent expensive calculations from degrading the performance of your Jetpack Compose application:

1. Use remember to Cache Results

The remember function allows you to store the result of a calculation across recompositions. This way, the calculation is only performed once, and the stored value is reused in subsequent recompositions unless the dependencies change.

import androidx.compose.runtime.*

@Composable
fun ExpensiveCalculationExample(input: Int) {
    val result = remember(input) {
        performExpensiveCalculation(input)
    }
    Text(text = "Result: $result")
}

fun performExpensiveCalculation(input: Int): Int {
    // Simulate an expensive calculation
    Thread.sleep(100) // Simulate a delay
    return input * 2
}

In this example, performExpensiveCalculation is only called when the input changes. The remember function caches the result, so it’s not re-executed on every recomposition.

2. Use rememberCoroutineScope for Asynchronous Operations

When dealing with asynchronous operations, such as network requests or database queries, avoid performing them directly in composable functions. Instead, use rememberCoroutineScope to manage a coroutine scope that survives recompositions.

import kotlinx.coroutines.*
import androidx.compose.runtime.*

@Composable
fun AsyncOperationExample() {
    val coroutineScope = rememberCoroutineScope()
    var data by remember { mutableStateOf("Loading...") }

    LaunchedEffect(key1 = true) {
        coroutineScope.launch {
            data = fetchDataFromNetwork()
        }
    }

    Text(text = "Data: $data")
}

suspend fun fetchDataFromNetwork(): String {
    delay(1000) // Simulate network delay
    return "Data fetched from network"
}

Here, LaunchedEffect ensures that the asynchronous operation is only executed once when the composable is first composed and relaunched when keys change, preventing repeated execution on recompositions. rememberCoroutineScope prevents the scope from being recreated on every recomposition, and any coroutines launched within are properly managed.

3. Use derivedStateOf for Complex Derived States

Sometimes, a state variable depends on multiple other state variables, and performing a calculation directly in the composable function can lead to unnecessary recompositions. Use derivedStateOf to create a derived state that is only updated when the dependent state variables actually change.

import androidx.compose.runtime.*

@Composable
fun DerivedStateExample(a: Int, b: Int) {
    val isEven by remember {
        derivedStateOf { (a + b) % 2 == 0 }
    }

    Text(text = "Is Even: $isEven")
}

In this example, isEven is only recalculated when either a or b changes, avoiding unnecessary recompositions if other parts of the composable recompose.

4. Defer Calculations to ViewModels or Repositories

Move expensive calculations and data transformations to ViewModels or repositories. This not only helps keep your composable functions clean but also centralizes business logic, making it easier to manage and test.

import androidx.lifecycle.ViewModel
import androidx.compose.runtime.*
import androidx.lifecycle.viewmodel.compose.viewModel

class MyViewModel : ViewModel() {
    private val _result = mutableStateOf(0)
    val result: State = _result

    fun performCalculation(input: Int) {
        // Perform the calculation on a background thread
        _result.value = performExpensiveCalculation(input)
    }

    private fun performExpensiveCalculation(input: Int): Int {
        // Simulate an expensive calculation
        Thread.sleep(100)
        return input * 2
    }
}

@Composable
fun ViewModelExample(input: Int) {
    val viewModel: MyViewModel = viewModel()
    
    //Trigger calculation if value of input changed. 
    LaunchedEffect(input){
         viewModel.performCalculation(input)
    }
   
    Text(text = "Result: ${viewModel.result.value}")
}

In this approach, the expensive calculation is performed in the ViewModel, and the composable function simply observes the result. Make sure heavy tasks inside the viewmodel get’s computed from a background thread to prevent blocking the UI thread. The LaunchedEffect helps to trigger the heavy tasks when the input values change

5. Use Custom Modifiers for Rendering Optimizations

For complex drawing or layout calculations, consider using custom modifiers to optimize rendering. This approach is useful when you need fine-grained control over how your UI elements are rendered.

import androidx.compose.ui.Modifier
import androidx.compose.ui.draw.drawWithCache
import androidx.compose.ui.graphics.Color
import androidx.compose.foundation.layout.Box
import androidx.compose.runtime.Composable
import androidx.compose.ui.tooling.preview.Preview

fun Modifier.customDraw(color: Color): Modifier = this.drawWithCache {
    onDrawWithContent {
        drawContent()
        drawRect(color = color)
    }
}

@Composable
fun CustomModifierExample() {
    Box(modifier = Modifier.size(100.dp).customDraw(Color.Red)) {
        // Content
    }
}

@Preview(showBackground = true)
@Composable
fun CustomModifierExamplePreview() {
    CustomModifierExample()
}

By using drawWithCache, the drawing logic is cached and only re-executed when necessary, optimizing the rendering process.

6. Consider Inline Functions Sparingly

While inline functions can sometimes improve performance by reducing function call overhead, they can also increase code size and lead to more recompositions if not used carefully. Ensure that the inline functions don’t inadvertently cause expensive calculations within composable functions to be re-executed unnecessarily.

Conclusion

Avoiding expensive calculations in Jetpack Compose is crucial for maintaining a smooth and responsive UI. By using techniques like remember, rememberCoroutineScope, derivedStateOf, moving calculations to ViewModels, and using custom modifiers for rendering optimizations, you can ensure that your Compose applications perform efficiently and provide an excellent user experience.