LazyListState


A state object that can be hoisted to control and observe scrolling.

In most cases, this will be created via rememberLazyListState.

Summary

Public companion properties

Saver<LazyListState, *>

The default Saver implementation for LazyListState.

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Public constructors

LazyListState(
    firstVisibleItemIndex: Int,
    firstVisibleItemScrollOffset: Int
)
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@ExperimentalFoundationApi
LazyListState(
    firstVisibleItemIndex: Int,
    firstVisibleItemScrollOffset: Int,
    prefetchStrategy: LazyListPrefetchStrategy
)
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Public functions

suspend Unit
animateScrollToItem(index: @IntRange(from = 0) Int, scrollOffset: Int)

Animate (smooth scroll) to the given item.

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open Float

Dispatch scroll delta in pixels avoiding all scroll related mechanisms.

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Unit
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open suspend Unit
scroll(scrollPriority: MutatePriority, block: suspend ScrollScope.() -> Unit)

Call this function to take control of scrolling and gain the ability to send scroll events via ScrollScope.scrollBy.

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suspend Unit
scrollToItem(index: @IntRange(from = 0) Int, scrollOffset: Int)

Instantly brings the item at index to the top of the viewport, offset by scrollOffset pixels.

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Public properties

open Boolean

Whether this ScrollableState can scroll backward (consume a negative delta).

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open Boolean

Whether this ScrollableState can scroll forward (consume a positive delta).

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Int

The index of the first item that is visible.

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Int

The scroll offset of the first visible item.

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InteractionSource

InteractionSource that will be used to dispatch drag events when this list is being dragged.

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open Boolean

Whether this ScrollableState is currently scrolling by gesture, fling or programmatically or not.

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LazyListLayoutInfo

The object of LazyListLayoutInfo calculated during the last layout pass.

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Public companion properties

Saver

val SaverSaver<LazyListState, *>

The default Saver implementation for LazyListState.

Public constructors

LazyListState

LazyListState(
    firstVisibleItemIndex: Int = 0,
    firstVisibleItemScrollOffset: Int = 0
)
Parameters
firstVisibleItemIndex: Int = 0

the initial value for LazyListState.firstVisibleItemIndex

firstVisibleItemScrollOffset: Int = 0

the initial value for LazyListState.firstVisibleItemScrollOffset

LazyListState

@ExperimentalFoundationApi
LazyListState(
    firstVisibleItemIndex: Int = 0,
    firstVisibleItemScrollOffset: Int = 0,
    prefetchStrategy: LazyListPrefetchStrategy = DefaultLazyListPrefetchStrategy()
)
Parameters
firstVisibleItemIndex: Int = 0

the initial value for LazyListState.firstVisibleItemIndex

firstVisibleItemScrollOffset: Int = 0

the initial value for LazyListState.firstVisibleItemScrollOffset

prefetchStrategy: LazyListPrefetchStrategy = DefaultLazyListPrefetchStrategy()

the LazyListPrefetchStrategy to use for prefetching content in this list

Public functions

animateScrollToItem

suspend fun animateScrollToItem(index: @IntRange(from = 0) Int, scrollOffset: Int = 0): Unit

Animate (smooth scroll) to the given item.

Parameters
index: @IntRange(from = 0) Int

the index to which to scroll. Must be non-negative.

scrollOffset: Int = 0

the offset that the item should end up after the scroll. Note that positive offset refers to forward scroll, so in a top-to-bottom list, positive offset will scroll the item further upward (taking it partly offscreen).

dispatchRawDelta

open fun dispatchRawDelta(delta: Float): Float

Dispatch scroll delta in pixels avoiding all scroll related mechanisms.

NOTE: unlike scroll, dispatching any delta with this method won't trigger nested scroll, won't stop ongoing scroll/drag animation and will bypass scrolling of any priority. This method will also ignore reverseDirection and other parameters set in scrollable.

This method is used internally for nested scrolling dispatch and other low level operations, allowing implementers of ScrollableState influence the consumption as suits them. Manually dispatching delta via this method will likely result in a bad user experience, you must prefer scroll method over this one.

Parameters
delta: Float

amount of scroll dispatched in the nested scroll process

Returns
Float

the amount of delta consumed

notifyPrefetchOnScroll

fun notifyPrefetchOnScroll(delta: Float, layoutInfo: LazyListLayoutInfo): Unit

scroll

open suspend fun scroll(scrollPriority: MutatePriority, block: suspend ScrollScope.() -> Unit): Unit

Call this function to take control of scrolling and gain the ability to send scroll events via ScrollScope.scrollBy. All actions that change the logical scroll position must be performed within a scroll block (even if they don't call any other methods on this object) in order to guarantee that mutual exclusion is enforced.

If scroll is called from elsewhere, this will be canceled.

scrollToItem

suspend fun scrollToItem(index: @IntRange(from = 0) Int, scrollOffset: Int = 0): Unit

Instantly brings the item at index to the top of the viewport, offset by scrollOffset pixels.

Parameters
index: @IntRange(from = 0) Int

the index to which to scroll. Must be non-negative.

scrollOffset: Int = 0

the offset that the item should end up after the scroll. Note that positive offset refers to forward scroll, so in a top-to-bottom list, positive offset will scroll the item further upward (taking it partly offscreen).

Public properties

canScrollBackward

open val canScrollBackwardBoolean

Whether this ScrollableState can scroll backward (consume a negative delta). This is typically false if the scroll position is equal to its minimum value, and true otherwise.

Note that true here does not imply that delta will be consumed - the ScrollableState may decide not to handle the incoming delta (such as if it is already being scrolled separately). Additionally, for backwards compatibility with previous versions of ScrollableState this value defaults to true.

import androidx.compose.foundation.layout.Column
import androidx.compose.foundation.layout.fillMaxWidth
import androidx.compose.foundation.lazy.LazyColumn
import androidx.compose.foundation.lazy.items
import androidx.compose.foundation.lazy.rememberLazyListState
import androidx.compose.material.Icon
import androidx.compose.material.Text
import androidx.compose.ui.graphics.graphicsLayer

val state = rememberLazyListState()
Column(Modifier.fillMaxWidth(), horizontalAlignment = Alignment.CenterHorizontally) {
    Icon(
        Icons.Filled.KeyboardArrowUp,
        null,
        Modifier.graphicsLayer {
            // Hide the icon if we cannot scroll backward (we are the start of the list)
            // We use graphicsLayer here to control the alpha so that we only redraw when this
            // value changes, instead of recomposing
            alpha = if (state.canScrollBackward) 1f else 0f
        },
        Color.Red
    )
    val items = (1..100).toList()
    LazyColumn(
        Modifier
            .weight(1f)
            .fillMaxWidth(), state
    ) {
        items(items) {
            Text("Item is $it")
        }
    }
    Icon(
        Icons.Filled.KeyboardArrowDown,
        null,
        Modifier.graphicsLayer {
            // Hide the icon if we cannot scroll forward (we are the end of the list)
            // We use graphicsLayer here to control the alpha so that we only redraw when this
            // value changes, instead of recomposing
            alpha = if (state.canScrollForward) 1f else 0f
        },
        Color.Red
    )
}

canScrollForward

open val canScrollForwardBoolean

Whether this ScrollableState can scroll forward (consume a positive delta). This is typically false if the scroll position is equal to its maximum value, and true otherwise.

Note that true here does not imply that delta will be consumed - the ScrollableState may decide not to handle the incoming delta (such as if it is already being scrolled separately). Additionally, for backwards compatibility with previous versions of ScrollableState this value defaults to true.

import androidx.compose.foundation.layout.Column
import androidx.compose.foundation.layout.fillMaxWidth
import androidx.compose.foundation.lazy.LazyColumn
import androidx.compose.foundation.lazy.items
import androidx.compose.foundation.lazy.rememberLazyListState
import androidx.compose.material.Icon
import androidx.compose.material.Text
import androidx.compose.ui.graphics.graphicsLayer

val state = rememberLazyListState()
Column(Modifier.fillMaxWidth(), horizontalAlignment = Alignment.CenterHorizontally) {
    Icon(
        Icons.Filled.KeyboardArrowUp,
        null,
        Modifier.graphicsLayer {
            // Hide the icon if we cannot scroll backward (we are the start of the list)
            // We use graphicsLayer here to control the alpha so that we only redraw when this
            // value changes, instead of recomposing
            alpha = if (state.canScrollBackward) 1f else 0f
        },
        Color.Red
    )
    val items = (1..100).toList()
    LazyColumn(
        Modifier
            .weight(1f)
            .fillMaxWidth(), state
    ) {
        items(items) {
            Text("Item is $it")
        }
    }
    Icon(
        Icons.Filled.KeyboardArrowDown,
        null,
        Modifier.graphicsLayer {
            // Hide the icon if we cannot scroll forward (we are the end of the list)
            // We use graphicsLayer here to control the alpha so that we only redraw when this
            // value changes, instead of recomposing
            alpha = if (state.canScrollForward) 1f else 0f
        },
        Color.Red
    )
}

firstVisibleItemIndex

val firstVisibleItemIndexInt

The index of the first item that is visible.

Note that this property is observable and if you use it in the composable function it will be recomposed on every change causing potential performance issues.

If you want to run some side effects like sending an analytics event or updating a state based on this value consider using "snapshotFlow":

import androidx.compose.foundation.lazy.rememberLazyListState
import androidx.compose.runtime.LaunchedEffect
import androidx.compose.runtime.snapshotFlow

val listState = rememberLazyListState()
LaunchedEffect(listState) {
    snapshotFlow { listState.firstVisibleItemIndex }
        .collect {
            // use the new index
        }
}

If you need to use it in the composition then consider wrapping the calculation into a derived state in order to only have recompositions when the derived value changes:

import androidx.compose.foundation.lazy.rememberLazyListState
import androidx.compose.runtime.derivedStateOf
import androidx.compose.runtime.remember

val listState = rememberLazyListState()
val isAtTop by remember {
    derivedStateOf {
        listState.firstVisibleItemIndex == 0 && listState.firstVisibleItemScrollOffset == 0
    }
}
if (!isAtTop) {
    ScrollToTopButton(listState)
}

firstVisibleItemScrollOffset

val firstVisibleItemScrollOffsetInt

The scroll offset of the first visible item. Scrolling forward is positive - i.e., the amount that the item is offset backwards.

Note that this property is observable and if you use it in the composable function it will be recomposed on every scroll causing potential performance issues.

See also
firstVisibleItemIndex

for samples with the recommended usage patterns.

interactionSource

val interactionSourceInteractionSource

InteractionSource that will be used to dispatch drag events when this list is being dragged. If you want to know whether the fling (or animated scroll) is in progress, use isScrollInProgress.

isScrollInProgress

open val isScrollInProgressBoolean

Whether this ScrollableState is currently scrolling by gesture, fling or programmatically or not.

layoutInfo

val layoutInfoLazyListLayoutInfo

The object of LazyListLayoutInfo calculated during the last layout pass. For example, you can use it to calculate what items are currently visible.

Note that this property is observable and is updated after every scroll or remeasure. If you use it in the composable function it will be recomposed on every change causing potential performance issues including infinity recomposition loop. Therefore, avoid using it in the composition.

If you want to run some side effects like sending an analytics event or updating a state based on this value consider using "snapshotFlow":

import androidx.compose.foundation.lazy.rememberLazyListState
import androidx.compose.runtime.LaunchedEffect
import androidx.compose.runtime.snapshotFlow

val listState = rememberLazyListState()
LaunchedEffect(listState) {
    snapshotFlow { listState.layoutInfo.totalItemsCount }
        .collect {
            // use the new items count
        }
}