Pull to refresh

The pull to refresh component allows users to drag downwards at the beginning of an app's content to refresh the data.

API surface

Use the PullToRefreshBox composable to implement pull-to-refresh, which acts as a container for your scrollable content. The following key parameters control the refresh behavior and appearance:

  • isRefreshing: A boolean value indicating whether the refresh action is currently in progress.
  • onRefresh: A lambda function that executes when the user initiates a refresh.
  • indicator: Customizes the indicator that is drawn on pull-to-refresh.

Basic example

This snippet demonstrates basic usage of PullToRefreshBox:

@Composable
fun PullToRefreshBasicSample(
    items: List<String>,
    isRefreshing: Boolean,
    onRefresh: () -> Unit,
    modifier: Modifier = Modifier
) {
    PullToRefreshBox(
        isRefreshing = isRefreshing,
        onRefresh = onRefresh,
        modifier = modifier
    ) {
        LazyColumn(Modifier.fillMaxSize()) {
            items(items) {
                ListItem({ Text(text = it) })
            }
        }
    }
}
PullToRefreshBox.kt

Key points about the code

  • PullToRefreshBox wraps a LazyColumn, which displays a list of strings.
  • PullToRefreshBox requires isRefreshing and onRefresh parameters.
  • The content within the PullToRefreshBox block represents the scrollable content.

Result

This video demonstrates the basic pull-to-refresh implementation from the preceding code:

Figure 1. A basic pull-to-refresh implementation on a list of items.

Advanced example: Customize indicator color

@Composable
fun PullToRefreshCustomStyleSample(
    items: List<String>,
    isRefreshing: Boolean,
    onRefresh: () -> Unit,
    modifier: Modifier = Modifier
) {
    val state = rememberPullToRefreshState()

    PullToRefreshBox(
        isRefreshing = isRefreshing,
        onRefresh = onRefresh,
        modifier = modifier,
        state = state,
        indicator = {
            Indicator(
                modifier = Modifier.align(Alignment.TopCenter),
                isRefreshing = isRefreshing,
                containerColor = MaterialTheme.colorScheme.primaryContainer,
                color = MaterialTheme.colorScheme.onPrimaryContainer,
                state = state
            )
        },
    ) {
        LazyColumn(Modifier.fillMaxSize()) {
            items(items) {
                ListItem({ Text(text = it) })
            }
        }
    }
}
PullToRefreshBox.kt

Key points about the code

  • The indicator color is customized through the containerColor and color properties in the indicator parameter.
  • rememberPullToRefreshState() manages the state of the refresh action. You use this state in conjunction with the indicator parameter.

Result

This video shows a pull-to-refresh implementation with a colored indicator:

Figure 2. A pull-to-refresh implementation with a custom style.

Advanced example: Create a fully customized indicator

You can create complex custom indicators by leveraging existing composables and animations.This snippet demonstrates how to create a fully custom indicator in your pull-to-refresh implementation:

@Composable
fun PullToRefreshCustomIndicatorSample(
    items: List<String>,
    isRefreshing: Boolean,
    onRefresh: () -> Unit,
    modifier: Modifier = Modifier
) {
    val state = rememberPullToRefreshState()

    PullToRefreshBox(
        isRefreshing = isRefreshing,
        onRefresh = onRefresh,
        modifier = modifier,
        state = state,
        indicator = {
            MyCustomIndicator(
                state = state,
                isRefreshing = isRefreshing,
                modifier = Modifier.align(Alignment.TopCenter)
            )
        }
    ) {
        LazyColumn(Modifier.fillMaxSize()) {
            items(items) {
                ListItem({ Text(text = it) })
            }
        }
    }
}

// ...
@Composable
fun MyCustomIndicator(
    state: PullToRefreshState,
    isRefreshing: Boolean,
    modifier: Modifier = Modifier,
) {
    Box(
        modifier = modifier.pullToRefreshIndicator(
            state = state,
            isRefreshing = isRefreshing,
            containerColor = PullToRefreshDefaults.containerColor,
            threshold = PositionalThreshold
        ),
        contentAlignment = Alignment.Center
    ) {
        Crossfade(
            targetState = isRefreshing,
            animationSpec = tween(durationMillis = CROSSFADE_DURATION_MILLIS),
            modifier = Modifier.align(Alignment.Center)
        ) { refreshing ->
            if (refreshing) {
                CircularProgressIndicator(Modifier.size(SPINNER_SIZE))
            } else {
                val distanceFraction = { state.distanceFraction.coerceIn(0f, 1f) }
                Icon(
                    imageVector = Icons.Filled.CloudDownload,
                    contentDescription = "Refresh",
                    modifier = Modifier
                        .size(18.dp)
                        .graphicsLayer {
                            val progress = distanceFraction()
                            this.alpha = progress
                            this.scaleX = progress
                            this.scaleY = progress
                        }
                )
            }
        }
    }
}
PullToRefreshBox.kt

Key points about the code

  • The previous snippet used the Indicator provided by the library. This snippet creates a custom indicator composable called MyCustomIndicator. In this composable, the pullToRefreshIndicator modifier handles positioning and triggering a refresh.
  • As in the previous snippet, the PullToRefreshState instance has been extracted, so the same instance can be passed to both the PullToRefreshBox and the pullToRefreshModifier.
  • The container color and the position threshold are used from the PullToRefreshDefaults class. This way, you can reuse the default behavior and styling from the Material library, while customizing only the elements you're interested in.
  • MyCustomIndicator uses Crossfade to transition between a cloud icon and a CircularProgressIndicator. The cloud icon scales up as the user pulls, and transitions to a CircularProgressIndicator when the refresh action begins.
    • targetState uses isRefreshing to determine which state to display (the cloud icon or the circular progress indicator).
    • animationSpec defines a tween animation for the transition, with a specified duration of CROSSFADE_DURATION_MILLIS.
    • state.distanceFraction represents how far the user has pulled down, ranging from 0f (no pull) to 1f (fully pulled).
    • The graphicsLayer modifier modifies scale and transparency.

Result

This video shows the custom indicator from the preceding code:

Figure 3. A pull-to-refresh implementation with a custom indicator.

Additional resources