commonMain.androidx.compose.foundation.lazy.LazyList.kt Maven / Gradle / Ivy
/*
* Copyright 2021 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package androidx.compose.foundation.lazy
import androidx.compose.foundation.ExperimentalFoundationApi
import androidx.compose.foundation.checkScrollableContainerConstraints
import androidx.compose.foundation.gestures.FlingBehavior
import androidx.compose.foundation.gestures.Orientation
import androidx.compose.foundation.gestures.ScrollableDefaults
import androidx.compose.foundation.internal.requirePreconditionNotNull
import androidx.compose.foundation.layout.Arrangement
import androidx.compose.foundation.layout.PaddingValues
import androidx.compose.foundation.layout.calculateEndPadding
import androidx.compose.foundation.layout.calculateStartPadding
import androidx.compose.foundation.lazy.layout.LazyLayout
import androidx.compose.foundation.lazy.layout.LazyLayoutMeasureScope
import androidx.compose.foundation.lazy.layout.StickyItemsPlacement
import androidx.compose.foundation.lazy.layout.calculateLazyLayoutPinnedIndices
import androidx.compose.foundation.lazy.layout.lazyLayoutBeyondBoundsModifier
import androidx.compose.foundation.lazy.layout.lazyLayoutSemantics
import androidx.compose.foundation.scrollingContainer
import androidx.compose.runtime.Composable
import androidx.compose.runtime.remember
import androidx.compose.runtime.rememberCoroutineScope
import androidx.compose.runtime.snapshots.Snapshot
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.graphics.GraphicsContext
import androidx.compose.ui.layout.MeasureResult
import androidx.compose.ui.layout.Placeable
import androidx.compose.ui.platform.LocalGraphicsContext
import androidx.compose.ui.platform.LocalLayoutDirection
import androidx.compose.ui.platform.LocalScrollCaptureInProgress
import androidx.compose.ui.unit.Constraints
import androidx.compose.ui.unit.IntOffset
import androidx.compose.ui.unit.constrainHeight
import androidx.compose.ui.unit.constrainWidth
import androidx.compose.ui.unit.offset
import kotlinx.coroutines.CoroutineScope
@OptIn(ExperimentalFoundationApi::class)
@Composable
internal fun LazyList(
/** Modifier to be applied for the inner layout */
modifier: Modifier,
/** State controlling the scroll position */
state: LazyListState,
/** The inner padding to be added for the whole content(not for each individual item) */
contentPadding: PaddingValues,
/** reverse the direction of scrolling and layout */
reverseLayout: Boolean,
/** The layout orientation of the list */
isVertical: Boolean,
/** fling behavior to be used for flinging */
flingBehavior: FlingBehavior,
/** Whether scrolling via the user gestures is allowed. */
userScrollEnabled: Boolean,
/** Number of items to layout before and after the visible items */
beyondBoundsItemCount: Int = 0,
/** The alignment to align items horizontally. Required when isVertical is true */
horizontalAlignment: Alignment.Horizontal? = null,
/** The vertical arrangement for items. Required when isVertical is true */
verticalArrangement: Arrangement.Vertical? = null,
/** The alignment to align items vertically. Required when isVertical is false */
verticalAlignment: Alignment.Vertical? = null,
/** The horizontal arrangement for items. Required when isVertical is false */
horizontalArrangement: Arrangement.Horizontal? = null,
/** The content of the list */
content: LazyListScope.() -> Unit
) {
val itemProviderLambda = rememberLazyListItemProviderLambda(state, content)
val semanticState = rememberLazyListSemanticState(state, isVertical)
val coroutineScope = rememberCoroutineScope()
val graphicsContext = LocalGraphicsContext.current
val stickyHeadersEnabled = !LocalScrollCaptureInProgress.current
val measurePolicy =
rememberLazyListMeasurePolicy(
itemProviderLambda,
state,
contentPadding,
reverseLayout,
isVertical,
beyondBoundsItemCount,
horizontalAlignment,
verticalAlignment,
horizontalArrangement,
verticalArrangement,
coroutineScope,
graphicsContext,
if (stickyHeadersEnabled) StickyItemsPlacement.StickToTopPlacement else null
)
val orientation = if (isVertical) Orientation.Vertical else Orientation.Horizontal
val reverseDirection =
ScrollableDefaults.reverseDirection(
LocalLayoutDirection.current,
orientation,
reverseLayout
)
LazyLayout(
modifier =
modifier
.then(state.remeasurementModifier)
.then(state.awaitLayoutModifier)
.lazyLayoutSemantics(
itemProviderLambda = itemProviderLambda,
state = semanticState,
orientation = orientation,
userScrollEnabled = userScrollEnabled,
reverseScrolling = reverseLayout,
)
.lazyLayoutBeyondBoundsModifier(
state =
rememberLazyListBeyondBoundsState(
state = state,
beyondBoundsItemCount = beyondBoundsItemCount
),
beyondBoundsInfo = state.beyondBoundsInfo,
reverseLayout = reverseLayout,
layoutDirection = LocalLayoutDirection.current,
orientation = orientation,
enabled = userScrollEnabled
)
.then(state.itemAnimator.modifier)
.scrollingContainer(
state = state,
orientation = orientation,
enabled = userScrollEnabled,
reverseDirection = reverseDirection,
flingBehavior = flingBehavior,
interactionSource = state.internalInteractionSource,
overscrollEffect = ScrollableDefaults.overscrollEffect()
),
prefetchState = state.prefetchState,
measurePolicy = measurePolicy,
itemProvider = itemProviderLambda
)
}
@ExperimentalFoundationApi
@Composable
private fun rememberLazyListMeasurePolicy(
/** Items provider of the list. */
itemProviderLambda: () -> LazyListItemProvider,
/** The state of the list. */
state: LazyListState,
/** The inner padding to be added for the whole content(nor for each individual item) */
contentPadding: PaddingValues,
/** reverse the direction of scrolling and layout */
reverseLayout: Boolean,
/** The layout orientation of the list */
isVertical: Boolean,
/** Number of items to layout before and after the visible items */
beyondBoundsItemCount: Int,
/** The alignment to align items horizontally */
horizontalAlignment: Alignment.Horizontal?,
/** The alignment to align items vertically */
verticalAlignment: Alignment.Vertical?,
/** The horizontal arrangement for items */
horizontalArrangement: Arrangement.Horizontal?,
/** The vertical arrangement for items */
verticalArrangement: Arrangement.Vertical?,
/** Scope for animations */
coroutineScope: CoroutineScope,
/** Used for creating graphics layers */
graphicsContext: GraphicsContext,
/** Scroll behavior for sticky items */
stickyItemsPlacement: StickyItemsPlacement?
) =
remember MeasureResult>(
state,
contentPadding,
reverseLayout,
isVertical,
horizontalAlignment,
verticalAlignment,
horizontalArrangement,
verticalArrangement,
graphicsContext,
stickyItemsPlacement,
) {
{ containerConstraints ->
state.measurementScopeInvalidator.attachToScope()
// Tracks if the lookahead pass has occurred
val hasLookaheadPassOccurred = state.hasLookaheadPassOccurred || isLookingAhead
checkScrollableContainerConstraints(
containerConstraints,
if (isVertical) Orientation.Vertical else Orientation.Horizontal
)
// resolve content paddings
val startPadding =
if (isVertical) {
contentPadding.calculateLeftPadding(layoutDirection).roundToPx()
} else {
// in horizontal configuration, padding is reversed by placeRelative
contentPadding.calculateStartPadding(layoutDirection).roundToPx()
}
val endPadding =
if (isVertical) {
contentPadding.calculateRightPadding(layoutDirection).roundToPx()
} else {
// in horizontal configuration, padding is reversed by placeRelative
contentPadding.calculateEndPadding(layoutDirection).roundToPx()
}
val topPadding = contentPadding.calculateTopPadding().roundToPx()
val bottomPadding = contentPadding.calculateBottomPadding().roundToPx()
val totalVerticalPadding = topPadding + bottomPadding
val totalHorizontalPadding = startPadding + endPadding
val totalMainAxisPadding =
if (isVertical) totalVerticalPadding else totalHorizontalPadding
val beforeContentPadding =
when {
isVertical && !reverseLayout -> topPadding
isVertical && reverseLayout -> bottomPadding
!isVertical && !reverseLayout -> startPadding
else -> endPadding // !isVertical && reverseLayout
}
val afterContentPadding = totalMainAxisPadding - beforeContentPadding
val contentConstraints =
containerConstraints.offset(-totalHorizontalPadding, -totalVerticalPadding)
val itemProvider = itemProviderLambda()
// this will update the scope used by the item composables
itemProvider.itemScope.setMaxSize(
width = contentConstraints.maxWidth,
height = contentConstraints.maxHeight
)
val spaceBetweenItemsDp =
if (isVertical) {
requirePreconditionNotNull(verticalArrangement) {
"null verticalArrangement when isVertical == true"
}
.spacing
} else {
requirePreconditionNotNull(horizontalArrangement) {
"null horizontalAlignment when isVertical == false"
}
.spacing
}
val spaceBetweenItems = spaceBetweenItemsDp.roundToPx()
val itemsCount = itemProvider.itemCount
// can be negative if the content padding is larger than the max size from constraints
val mainAxisAvailableSize =
if (isVertical) {
containerConstraints.maxHeight - totalVerticalPadding
} else {
containerConstraints.maxWidth - totalHorizontalPadding
}
val visualItemOffset =
if (!reverseLayout || mainAxisAvailableSize > 0) {
IntOffset(startPadding, topPadding)
} else {
// When layout is reversed and paddings together take >100% of the available
// space,
// layout size is coerced to 0 when positioning. To take that space into
// account,
// we offset start padding by negative space between paddings.
IntOffset(
if (isVertical) startPadding else startPadding + mainAxisAvailableSize,
if (isVertical) topPadding + mainAxisAvailableSize else topPadding
)
}
val measuredItemProvider =
object :
LazyListMeasuredItemProvider(
contentConstraints,
isVertical,
itemProvider,
this
) {
override fun createItem(
index: Int,
key: Any,
contentType: Any?,
placeables: List,
constraints: Constraints
): LazyListMeasuredItem {
// we add spaceBetweenItems as an extra spacing for all items apart from the
// last one so
// the lazy list measuring logic will take it into account.
val spacing = if (index == itemsCount - 1) 0 else spaceBetweenItems
return LazyListMeasuredItem(
index = index,
placeables = placeables,
isVertical = isVertical,
horizontalAlignment = horizontalAlignment,
verticalAlignment = verticalAlignment,
layoutDirection = layoutDirection,
reverseLayout = reverseLayout,
beforeContentPadding = beforeContentPadding,
afterContentPadding = afterContentPadding,
spacing = spacing,
visualOffset = visualItemOffset,
key = key,
contentType = contentType,
animator = state.itemAnimator,
constraints = constraints
)
}
}
val firstVisibleItemIndex: Int
val firstVisibleScrollOffset: Int
Snapshot.withoutReadObservation {
firstVisibleItemIndex =
state.updateScrollPositionIfTheFirstItemWasMoved(
itemProvider,
state.firstVisibleItemIndex
)
firstVisibleScrollOffset = state.firstVisibleItemScrollOffset
}
val pinnedItems =
itemProvider.calculateLazyLayoutPinnedIndices(
pinnedItemList = state.pinnedItems,
beyondBoundsInfo = state.beyondBoundsInfo
)
val scrollToBeConsumed =
if (isLookingAhead || !hasLookaheadPassOccurred) {
state.scrollToBeConsumed
} else {
state.scrollDeltaBetweenPasses
}
// todo: wrap with snapshot when b/341782245 is resolved
val measureResult =
measureLazyList(
itemsCount = itemsCount,
measuredItemProvider = measuredItemProvider,
mainAxisAvailableSize = mainAxisAvailableSize,
beforeContentPadding = beforeContentPadding,
afterContentPadding = afterContentPadding,
spaceBetweenItems = spaceBetweenItems,
firstVisibleItemIndex = firstVisibleItemIndex,
firstVisibleItemScrollOffset = firstVisibleScrollOffset,
scrollToBeConsumed = scrollToBeConsumed,
constraints = contentConstraints,
isVertical = isVertical,
verticalArrangement = verticalArrangement,
horizontalArrangement = horizontalArrangement,
reverseLayout = reverseLayout,
density = this,
itemAnimator = state.itemAnimator,
beyondBoundsItemCount = beyondBoundsItemCount,
pinnedItems = pinnedItems,
hasLookaheadPassOccurred = hasLookaheadPassOccurred,
isLookingAhead = isLookingAhead,
postLookaheadLayoutInfo = state.postLookaheadLayoutInfo,
coroutineScope = coroutineScope,
placementScopeInvalidator = state.placementScopeInvalidator,
graphicsContext = graphicsContext,
stickyItemsPlacement = stickyItemsPlacement,
layout = { width, height, placement ->
layout(
containerConstraints.constrainWidth(width + totalHorizontalPadding),
containerConstraints.constrainHeight(height + totalVerticalPadding),
emptyMap(),
placement
)
}
)
state.applyMeasureResult(measureResult, isLookingAhead)
measureResult
}
}
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