Using `remember` and `derivedStateOf` for Efficiency in Jetpack Compose

Jetpack Compose is a modern UI toolkit for building native Android applications using a declarative approach. It simplifies UI development, making it more intuitive and efficient. However, as applications grow in complexity, performance optimization becomes critical to ensure a smooth user experience.

Two essential tools for optimizing recomposition in Jetpack Compose are remember and derivedStateOf. These functions help manage state efficiently, reduce unnecessary recompositions, and enhance app performance. In this post, we will explore how to use remember and derivedStateOf effectively and when to choose one over the other.

Understanding Recomposition in Jetpack Compose

Before diving into remember and derivedStateOf, it’s crucial to understand recomposition. In Jetpack Compose, the UI updates dynamically when state changes. Recomposition is the process where the framework re-executes composable functions to reflect these updates. However, excessive recomposition can lead to performance issues, making optimizations necessary.

For instance, if a composable function is triggered to recompose too frequently, it can cause UI lag, increased CPU usage, and inefficient memory utilization. This is where remember and derivedStateOf come into play.

The Role of remember in Jetpack Compose

What is remember?

The remember function in Jetpack Compose helps retain values across recompositions. It ensures that an object is not re-created every time a composable function recomposes unless its dependencies change.

Basic Usage of remember

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

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

Explanation:

• The remember function ensures that count is retained during recomposition.
• Without remember, count would reset to 0 every time the function recomposes.

When to Use remember

Use remember when you need to:

• Retain UI state across recompositions.
• Optimize performance by avoiding redundant object re-creation.
• Store local states within a composable function.

Understanding derivedStateOf

What is derivedStateOf?

The derivedStateOf function is an optimization mechanism that helps create derived state values efficiently. It ensures that derived states are only recomputed when their dependencies change, reducing unnecessary calculations and recompositions.

Why Use derivedStateOf?

In some cases, a state might depend on another state but should not trigger recomposition on every change. derivedStateOf helps ensure that recomposition only occurs when the computed value actually changes.

Example Usage of derivedStateOf

@Composable
fun ListWithExpensiveComputation(items: List<String>) {
    var query by remember { mutableStateOf("") }
    
    val filteredItems by remember(query) {
        derivedStateOf {
            items.filter { it.contains(query, ignoreCase = true) }
        }
    }

    Column {
        TextField(value = query, onValueChange = { query = it })
        LazyColumn {
            items(filteredItems) { item ->
                Text(item)
            }
        }
    }
}

Explanation:

• The filteredItems state is derived from query and items.
• Without derivedStateOf, filteredItems would be recomputed on every recomposition, even if query has not changed.
• Using derivedStateOf, filteredItems is only recalculated when query actually changes, improving efficiency.

When to Use derivedStateOf

Use derivedStateOf when:

• You have expensive computations that should only run when necessary.
• You want to avoid redundant state updates triggering recompositions.
• You need to optimize performance when filtering, sorting, or transforming data.

Comparing remember and derivedStateOf

Both functions play a crucial role in optimizing recompositions, but they serve different purposes.

Best Practices for Using remember and derivedStateOf

1. Use remember to Persist State: Use remember for values that should persist across recompositions but do not depend on external calculations.

2. Use derivedStateOf for Expensive Computations: If a state is derived from another and involves costly operations, wrap it inside derivedStateOf to avoid unnecessary recalculations.

3. Minimize Dependencies: Ensure that remember and derivedStateOf are only dependent on necessary values. Extra dependencies can lead to unnecessary recompositions.

4. Leverage remember with mutableStateOf: When using mutableStateOf, always wrap it with remember to prevent unintended resets.

5. Profile and Optimize: Use tools like Compose Compiler Metrics and Layout Inspector to identify unnecessary recompositions and optimize state management accordingly.

Conclusion

Optimizing recompositions is crucial for building efficient and responsive Jetpack Compose applications. The remember function helps persist state across recompositions, while derivedStateOf ensures derived values are only recomputed when needed. By using these tools effectively, you can significantly improve app performance and user experience.

By understanding when and how to use remember and derivedStateOf, you can avoid common pitfalls and ensure your Jetpack Compose applications run efficiently. Happy coding!

Further Reading

• Jetpack Compose State Management
• Optimizing Compose Performance
• Understanding Recomposition in Jetpack Compose

Do you have any questions or additional insights about using remember and derivedStateOf? Feel free to share your thoughts in the comments!