Implement Sticky Scrolling in Jetpack Compose LazyColumn

Jetpack Compose, Android’s modern toolkit for building native UI, has revolutionized the way developers create user interfaces. Among its many powerful components is the LazyColumn, which provides a highly efficient and flexible way to display vertical lists. One common UI pattern in such lists is "sticky scrolling," where certain headers or items stay pinned at the top as you scroll through the content. Implementing this feature in Jetpack Compose is both straightforward and powerful when done correctly.

In this blog post, we’ll explore how to implement sticky scrolling in a LazyColumn, covering in-depth concepts, best practices, and advanced use cases. By the end of this article, you’ll be equipped to create smooth and visually appealing sticky headers in your Jetpack Compose applications.

What Is Sticky Scrolling?

Sticky scrolling refers to a UX behavior where certain list items (usually section headers) stick to the top of the scrolling container while the user scrolls through the list. This pattern enhances the navigation experience, especially in content-heavy apps like news readers, e-commerce platforms, or social media feeds.

For example:

In a contacts app, headers representing the first letter of names ("A", "B", "C", etc.) stick to the top as you scroll through a list of contacts.
In an e-commerce app, category headers stay visible while scrolling through the products in that category.

Jetpack Compose provides efficient tools to implement sticky scrolling behavior using LazyColumn and its associated APIs.

Setting Up Your Jetpack Compose Project

Before diving into the implementation, ensure your project is set up to use Jetpack Compose:

Dependencies: Add the necessary dependencies in your build.gradle file:

implementation "androidx.compose.ui:ui:1.x.x"
implementation "androidx.compose.foundation:foundation:1.x.x"
implementation "androidx.compose.material:material:1.x.x"
implementation "androidx.compose.runtime:runtime-livedata:1.x.x"

Kotlin Compatibility: Use Kotlin 1.7.0 or later for compatibility with the latest Jetpack Compose features.
Minimum SDK: Ensure your app targets at least API level 21 (Lollipop).

Core Components of Sticky Scrolling in `LazyColumn`

To implement sticky scrolling, you’ll primarily use these Jetpack Compose components:

1. `LazyColumn`

The LazyColumn efficiently renders only the visible items on the screen, making it ideal for long lists.

2. `StickyHeader`

Jetpack Compose offers a StickyHeader composable (part of the foundation library) that allows you to define headers that stick to the top during scrolling.

Here’s a basic example:

LazyColumn {
    stickyHeader {
        Text(
            text = "Sticky Header",
            modifier = Modifier
                .fillMaxWidth()
                .background(Color.Gray)
                .padding(16.dp),
            style = MaterialTheme.typography.h6,
            color = Color.White
        )
    }

    items(100) { index ->
        Text(
            text = "Item #$index",
            modifier = Modifier.padding(16.dp)
        )
    }
}

In this example:

The stickyHeader composable ensures the header stays pinned at the top as you scroll.
The items block generates list items dynamically.

Advanced Implementation: Dynamic Section Headers

In real-world scenarios, sticky headers are often dynamic, such as displaying categories in a shopping app or dates in a chat app. Let’s create a more advanced example with dynamic headers.

Data Structure

We’ll use a map where each key is a header and the value is a list of items under that header:

val data = mapOf(
    "A" to listOf("Alice", "Andrew", "Amanda"),
    "B" to listOf("Bob", "Brenda", "Bryan"),
    "C" to listOf("Charlie", "Catherine", "Chris")
)

Composable Code

Here’s how to create a LazyColumn with sticky headers:

@Composable
fun StickyHeaderList(data: Map<String, List<String>>) {
    LazyColumn {
        data.forEach { (header, items) ->
            stickyHeader {
                Text(
                    text = header,
                    modifier = Modifier
                        .fillMaxWidth()
                        .background(Color.LightGray)
                        .padding(8.dp),
                    style = MaterialTheme.typography.subtitle1
                )
            }

            items(items) { item ->
                Text(
                    text = item,
                    modifier = Modifier
                        .fillMaxWidth()
                        .padding(16.dp),
                    style = MaterialTheme.typography.body1
                )
            }
        }
    }
}

Explanation

Dynamic Headers: The forEach loop iterates through the data map, creating a stickyHeader for each key and rendering items for each value.
Styling: Use Modifier for spacing, padding, and background colors to distinguish headers and items visually.

Best Practices for Sticky Scrolling in Jetpack Compose

1. Optimize Performance

Avoid Over-Rendering: Ensure that expensive composables inside LazyColumn are optimized to prevent frame drops.
Use Keys: Assign unique keys to list items to help Compose efficiently track changes.
```
items(items, key = { it.id }) { item ->
    // Render item
}
```

2. Design for Accessibility

Add contentDescription for sticky headers to support screen readers.
Use high contrast colors for better readability.

3. Test Across Devices

Test sticky scrolling behavior on devices with different screen sizes and orientations to ensure a consistent experience.

4. Use LazyColumn State for Enhanced UX

Capture the scroll position using rememberLazyListState for advanced interactions.

val listState = rememberLazyListState()

LazyColumn(state = listState) {
    // Content
}

// Observe scroll state for additional features
val firstVisibleItemIndex = listState.firstVisibleItemIndex

Advanced Use Case: Animated Sticky Headers

To make your UI more dynamic, you can add animations to sticky headers using Compose’s Modifier.graphicsLayer or animateFloatAsState. For instance, you could shrink the header size as it scrolls out of view:

@Composable
fun AnimatedStickyHeader(header: String, progress: Float) {
    val scale = animateFloatAsState(targetValue = progress).value

    Text(
        text = header,
        modifier = Modifier
            .fillMaxWidth()
            .graphicsLayer(scaleX = scale, scaleY = scale)
            .background(Color.Gray)
            .padding(16.dp),
        style = MaterialTheme.typography.h6
    )
}

Combine this with LazyListState to calculate progress based on the scroll position.

Conclusion

Sticky scrolling in Jetpack Compose is a versatile feature that enhances the usability and aesthetics of your app’s UI. By leveraging LazyColumn and stickyHeader, you can create dynamic and performant lists that cater to a variety of use cases. Whether you’re building a chat app, a shopping app, or a content aggregator, implementing sticky headers ensures a polished and intuitive user experience.

Try integrating these techniques into your next Jetpack Compose project, and experiment with advanced features like animations to make your app truly stand out.

If you found this guide helpful, share it with your fellow developers and leave a comment below with your thoughts or questions!