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Make sure you are using this in your Jetpack Compose ‘LazyColumn’
Introduction

If you’re working with lists in Jetpack Compose, you’ve probably used LazyColumn. It’s a fantastic tool for efficiently rendering large lists of data with minimal performance overhead. But did you know there’s a simple one-line trick that can dramatically improve the performance of your LazyColumn?

This article will show you why using keys in a LazyColumn is a must, how to use it, and what benefits it brings to your app.

Why You Should Use Keys

When working with LazyColumn, each item in the list is associated with a specific position. By default, Jetpack Compose tracks items based on their index in the list. This works fine in static lists, but if your list is dynamic (e.g., items can be added, removed, or reordered), this approach can lead to unnecessary recompositions and a suboptimal user experience.

Using keys ensures that Compose can uniquely identify each item in the list, even when the data set changes. This allows Compose to reuse composables effectively, reducing recompositions and improving overall performance.

The One Line Trick: Use Keys

Here’s how you can implement keys in your LazyColumn:

LazyColumn {
    items(items = yourList, key = { it.id }) { item ->
        // Your item UI here
        Text(text = item.name)
    }
}

That’s it! By providing a unique key for each item, you’ve optimized your LazyColumn.

Key Benefits
1. Improved Performance

When you use keys, Compose can intelligently manage item recompositions. It knows which composables need to be updated and which can be reused, reducing unnecessary redraws and improving scrolling performance.

2. Accurate State Preservation

If your list items have internal state (e.g., text in an EditText), using keys ensures that these states are preserved correctly, even when the list is reordered or updated.

3. Smooth User Experience

With better performance and accurate state management, your app will feel smoother and more responsive to users.

When to Use Keys

You should always use keys in a LazyColumn when:

  • Your list data is dynamic and can change (e.g., add/remove/reorder items).
  • Your list items have internal state that must be preserved.
  • You’re working on an app where performance is critical (which is almost always!).
Common Mistakes
Not Using Keys at All

If you omit keys, Compose will rely on the default behavior of using indices, which can cause incorrect state preservation and performance issues.

Using Non-Unique Keys

Ensure that the key you provide is unique for each item. Duplicate keys will lead to unexpected behavior and bugs.

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Additional Considerations

While keys are essential for dynamic lists, it’s also a good practice to use them in static lists where you expect future updates. This makes your code more robust and ready for future changes. Moreover, using meaningful keys based on your data model (e.g., an id or unique identifier) is a clean way to ensure your app is scalable and maintainable.

It’s also worth noting that keys are not limited to LazyColumn. They can also be used in LazyRow or other composable lists to achieve similar benefits.

Conclusion

Using keys in your LazyColumn is a simple yet powerful optimization that can significantly enhance the performance and user experience of your app. It’s one of those subtle details that separates good apps from great ones.

So, the next time you use a LazyColumn, remember to include keys. It’s just one line of code, but it makes a world of difference!

Do you have any other tricks for optimizing LazyColumn? Share them in the comments below!

Dobri Kostadinov
Android Consultant | Trainer
Email me | Follow me on LinkedIn | Follow me on Medium | Buy me a coffee

This article is previously published on proandroiddev.com.

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