Implementing LazyColumn in Jetpack Compose Scaffold: Best Approach

Jetpack Compose has revolutionized Android UI development with its declarative approach. One of its most powerful components is the LazyColumn, a highly efficient way to display long lists of data. When combined with a Scaffold — a layout that provides a structured UI foundation with toolbars, drawers, and more — developers can create responsive, scalable, and elegant user interfaces.

This blog post explores the best practices for implementing LazyColumn within a Scaffold, ensuring optimal performance and a seamless developer experience. Let’s dive into the intricacies of combining these two components to build production-ready Android apps.

Why Combine LazyColumn with Scaffold?

The Scaffold component in Jetpack Compose is designed to provide a consistent structure for your app. It’s often used to implement:

  • TopAppBar for navigation and titles.

  • BottomNavigation for switching between screens.

  • FloatingActionButton (FAB) for primary actions.

  • Snackbars and other contextual UI elements.

When working with large data sets, LazyColumn is the go-to choice for efficiently rendering list items without unnecessary memory overhead. Combining LazyColumn with Scaffold allows you to:

  1. Leverage Scaffold's structured layout to position UI elements like toolbars and FABs.

  2. Use LazyColumn to render dynamic content within the main content area of the Scaffold.

  3. Achieve a cohesive and responsive design that adheres to Material Design principles.

Setting Up the Basics: Scaffold with LazyColumn

Before diving into advanced use cases, let’s start with a simple implementation:

@Composable
fun ScaffoldWithLazyColumn() {
    Scaffold(
        topBar = {
            TopAppBar(title = { Text("LazyColumn Example") })
        },
        floatingActionButton = {
            FloatingActionButton(onClick = { /* TODO */ }) {
                Icon(Icons.Default.Add, contentDescription = "Add")
            }
        }
    ) { innerPadding ->
        LazyColumn(
            contentPadding = innerPadding,
            verticalArrangement = Arrangement.spacedBy(8.dp)
        ) {
            items(100) { index ->
                ListItem(index)
            }
        }
    }
}

@Composable
fun ListItem(index: Int) {
    Text(
        text = "Item #$index",
        modifier = Modifier
            .fillMaxWidth()
            .padding(16.dp),
        style = MaterialTheme.typography.body1
    )
}

Key Points:

  1. Inner Padding: The innerPadding parameter ensures the LazyColumn content respects the padding provided by the Scaffold (e.g., space for the TopAppBar or BottomNavigation).

  2. Content Spacing: Arrangement.spacedBy creates visually appealing spacing between items in the LazyColumn.

Handling Complex Layouts

In real-world applications, you may need to incorporate multiple UI elements while maintaining a fluid and responsive design. For instance, adding a BottomNavigation or a Snackbar can complicate layout management.

Here’s an example that includes BottomNavigation:

@Composable
fun ScaffoldWithBottomNavigation() {
    val navItems = listOf("Home", "Profile", "Settings")
    var selectedItem by remember { mutableStateOf(0) }

    Scaffold(
        topBar = {
            TopAppBar(title = { Text("Scaffold with Navigation") })
        },
        bottomBar = {
            BottomNavigation {
                navItems.forEachIndexed { index, label ->
                    BottomNavigationItem(
                        icon = { Icon(Icons.Default.Home, contentDescription = null) },
                        label = { Text(label) },
                        selected = selectedItem == index,
                        onClick = { selectedItem = index }
                    )
                }
            }
        }
    ) { innerPadding ->
        LazyColumn(
            contentPadding = innerPadding,
            verticalArrangement = Arrangement.spacedBy(8.dp)
        ) {
            items(50) { index ->
                ListItem(index)
            }
        }
    }
}

Challenges Addressed:

  1. Dynamic Bottom Navigation: The BottomNavigation dynamically updates the UI based on user interactions.

  2. Seamless Padding: The innerPadding ensures the LazyColumn respects the space occupied by the BottomNavigation.

Optimizing Performance

While LazyColumn is efficient, improper usage can lead to performance issues in complex UIs. Here are some optimization tips:

1. Use Stable Keys

When dealing with dynamic data, provide stable keys to the LazyColumn items to improve UI updates:

LazyColumn {
    items(items = myList, key = { it.id }) { item ->
        ListItem(item)
    }
}

2. Avoid Heavy Composable Recomposition

Use remember and derivedStateOf to minimize recompositions:

val filteredList by remember(myList, searchQuery) {
    derivedStateOf {
        myList.filter { it.contains(searchQuery) }
    }
}

LazyColumn {
    items(filteredList) { item ->
        ListItem(item)
    }
}

3. LazyColumn Inside Constraint Layouts

When using LazyColumn with ConstraintLayout, make sure constraints don’t override its scrolling behavior:

ConstraintLayout {
    val (list, fab) = createRefs()

    LazyColumn(
        modifier = Modifier.constrainAs(list) {
            top.linkTo(parent.top)
            bottom.linkTo(parent.bottom)
        }
    ) {
        items(20) { index ->
            ListItem(index)
        }
    }

    FloatingActionButton(
        onClick = {},
        modifier = Modifier.constrainAs(fab) {
            end.linkTo(parent.end, margin = 16.dp)
            bottom.linkTo(parent.bottom, margin = 16.dp)
        }
    ) {
        Icon(Icons.Default.Add, contentDescription = null)
    }
}

Advanced Use Cases

1. Nested Scrollable Components

Handling nested scrolling, such as a LazyColumn inside a ScrollableColumn, requires careful management using Modifier.nestedScroll().

2. Dynamic Content Loading

For infinite scrolling, detect the end of the list and trigger data loading:

val listState = rememberLazyListState()

LazyColumn(state = listState) {
    items(data) { item ->
        ListItem(item)
    }
}

LaunchedEffect(listState) {
    snapshotFlow { listState.layoutInfo.visibleItemsInfo.lastOrNull()?.index }
        .collect { lastVisibleIndex ->
            if (lastVisibleIndex == data.lastIndex) {
                loadMoreItems()
            }
        }
}

Conclusion

Integrating LazyColumn with Scaffold in Jetpack Compose unlocks powerful UI possibilities for Android developers. By adhering to best practices, such as respecting Scaffold padding, optimizing performance, and implementing dynamic content loading, you can create polished, high-performing applications.

Jetpack Compose continues to simplify Android development while enabling complex, modern designs. Mastering its components like LazyColumn and Scaffold is a must for any developer aiming to build scalable and efficient Android apps.

What’s your favorite way to use LazyColumn with Scaffold? Let us know in the comments below!