/*
* 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.assertNotNestingScrollableContainers
import androidx.compose.foundation.clipScrollableContainer
import androidx.compose.foundation.gestures.FlingBehavior
import androidx.compose.foundation.gestures.Orientation
import androidx.compose.foundation.gestures.OverScrollController
import androidx.compose.foundation.gestures.rememberOverScrollController
import androidx.compose.foundation.gestures.scrollable
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.layout.padding
import androidx.compose.foundation.lazy.layout.LazyLayout
import androidx.compose.foundation.lazy.layout.LazyMeasurePolicy
import androidx.compose.foundation.lazy.layout.rememberLazyLayoutPrefetchPolicy
import androidx.compose.foundation.lazy.layout.rememberLazyLayoutState
import androidx.compose.runtime.Composable
import androidx.compose.runtime.State
import androidx.compose.runtime.remember
import androidx.compose.runtime.rememberCoroutineScope
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.geometry.Size
import androidx.compose.ui.layout.IntrinsicMeasureScope
import androidx.compose.ui.node.Ref
import androidx.compose.ui.platform.LocalLayoutDirection
import androidx.compose.ui.unit.Constraints
import androidx.compose.ui.unit.Density
import androidx.compose.ui.unit.LayoutDirection
@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,
/** 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 overScrollController = rememberOverScrollController()
val itemScope: Ref<LazyItemScopeImpl> = remember { Ref() }
val stateOfItemsProvider = rememberStateOfItemsProvider(state, content, itemScope)
val scope = rememberCoroutineScope()
val placementAnimator = remember(state, isVertical) {
LazyListItemPlacementAnimator(scope, isVertical)
}
state.placementAnimator = placementAnimator
val measurePolicy = rememberLazyListMeasurePolicy(
stateOfItemsProvider,
itemScope,
state,
overScrollController,
contentPadding,
reverseLayout,
isVertical,
horizontalAlignment,
verticalAlignment,
horizontalArrangement,
verticalArrangement,
placementAnimator
)
state.prefetchPolicy = rememberLazyLayoutPrefetchPolicy()
val innerState = rememberLazyLayoutState().also { state.innerState = it }
val itemsProvider = stateOfItemsProvider.value
if (itemsProvider.itemsCount > 0) {
state.updateScrollPositionIfTheFirstItemWasMoved(itemsProvider)
}
LazyLayout(
modifier = modifier
.lazyListSemantics(
stateOfItemsProvider = stateOfItemsProvider,
state = state,
coroutineScope = scope,
isVertical = isVertical,
reverseScrolling = reverseLayout
)
.clipScrollableContainer(isVertical)
.scrollable(
orientation = if (isVertical) Orientation.Vertical else Orientation.Horizontal,
reverseDirection = run {
// A finger moves with the content, not with the viewport. Therefore,
// always reverse once to have "natural" gesture that goes reversed to layout
var reverseDirection = !reverseLayout
// But if rtl and horizontal, things move the other way around
val isRtl = LocalLayoutDirection.current == LayoutDirection.Rtl
if (isRtl && !isVertical) {
reverseDirection = !reverseDirection
}
reverseDirection
},
interactionSource = state.internalInteractionSource,
flingBehavior = flingBehavior,
state = state,
overScrollController = overScrollController
)
.padding(contentPadding),
state = innerState,
prefetchPolicy = state.prefetchPolicy,
measurePolicy = measurePolicy,
itemsProvider = { stateOfItemsProvider.value }
)
}
@Composable
private fun rememberLazyListMeasurePolicy(
/** State containing the items provider of the list. */
stateOfItemsProvider: State<LazyListItemsProvider>,
/** Value holder for the item scope used to compose items. */
itemScope: Ref<LazyItemScopeImpl>,
/** The state of the list. */
state: LazyListState,
/** The overscroll controller. */
overScrollController: OverScrollController,
/** 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,
/** The alignment to align items horizontally. Required when isVertical is true */
horizontalAlignment: Alignment.Horizontal? = 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 vertical arrangement for items. Required when isVertical is true */
verticalArrangement: Arrangement.Vertical? = null,
/** Item placement animator. Should be notified with the measuring result */
placementAnimator: LazyListItemPlacementAnimator
) = remember(
state,
overScrollController,
contentPadding,
reverseLayout,
isVertical,
horizontalAlignment,
verticalAlignment,
horizontalArrangement,
verticalArrangement,
placementAnimator
) {
LazyMeasurePolicy { placeablesProvider, constraints ->
constraints.assertNotNestingScrollableContainers(isVertical)
val itemsProvider = stateOfItemsProvider.value
state.updateScrollPositionIfTheFirstItemWasMoved(itemsProvider)
// Update the state's cached Density
state.density = this
// this will update the scope object if the constrains have been changed
itemScope.update(this, constraints)
val rawBeforeContentPadding = if (isVertical) {
contentPadding.calculateTopPadding()
} else {
contentPadding.calculateStartPadding(layoutDirection)
}.roundToPx()
val rawAfterContentPadding = if (isVertical) {
contentPadding.calculateBottomPadding()
} else {
contentPadding.calculateEndPadding(layoutDirection)
}.roundToPx()
val beforeContentPadding =
if (reverseLayout) rawAfterContentPadding else rawBeforeContentPadding
val afterContentPadding =
if (reverseLayout) rawBeforeContentPadding else rawAfterContentPadding
val mainAxisMaxSize = (if (isVertical) constraints.maxHeight else constraints.maxWidth)
val spaceBetweenItemsDp = if (isVertical) {
requireNotNull(verticalArrangement).spacing
} else {
requireNotNull(horizontalArrangement).spacing
}
val spaceBetweenItems = spaceBetweenItemsDp.roundToPx()
val itemsCount = itemsProvider.itemsCount
val itemProvider = LazyMeasuredItemProvider(
constraints,
isVertical,
itemsProvider,
placeablesProvider
) { index, key, placeables ->
// 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.value == itemsCount - 1) 0 else spaceBetweenItems
LazyMeasuredItem(
index = index.value,
placeables = placeables,
isVertical = isVertical,
horizontalAlignment = horizontalAlignment,
verticalAlignment = verticalAlignment,
layoutDirection = layoutDirection,
reverseLayout = reverseLayout,
beforeContentPadding = beforeContentPadding,
afterContentPadding = afterContentPadding,
spacing = spacing,
key = key,
placementAnimator = placementAnimator
)
}
state.prefetchPolicy?.constraints = itemProvider.childConstraints
measureLazyList(
itemsCount = itemsCount,
itemProvider = itemProvider,
mainAxisMaxSize = mainAxisMaxSize,
beforeContentPadding = beforeContentPadding,
afterContentPadding = afterContentPadding,
firstVisibleItemIndex = state.firstVisibleItemIndexNonObservable,
firstVisibleItemScrollOffset = state.firstVisibleItemScrollOffsetNonObservable,
scrollToBeConsumed = state.scrollToBeConsumed,
constraints = constraints,
isVertical = isVertical,
headerIndexes = itemsProvider.headerIndexes,
verticalArrangement = verticalArrangement,
horizontalArrangement = horizontalArrangement,
reverseLayout = reverseLayout,
density = this,
layoutDirection = layoutDirection,
placementAnimator = placementAnimator,
layout = { width, height, placement -> layout(width, height, emptyMap(), placement) }
).also {
state.applyMeasureResult(it)
refreshOverScrollInfo(overScrollController, it, contentPadding)
}.lazyLayoutMeasureResult
}
}
private fun Ref<LazyItemScopeImpl>.update(density: Density, constraints: Constraints) {
val value = value
if (value == null || value.density != density || value.constraints != constraints) {
this.value = LazyItemScopeImpl(density, constraints)
}
}
private fun IntrinsicMeasureScope.refreshOverScrollInfo(
overScrollController: OverScrollController,
result: LazyListMeasureResult,
contentPadding: PaddingValues
) {
val verticalPadding =
contentPadding.calculateTopPadding() +
contentPadding.calculateBottomPadding()
val horizontalPadding =
contentPadding.calculateLeftPadding(layoutDirection) +
contentPadding.calculateRightPadding(layoutDirection)
val canScrollForward = result.canScrollForward
val canScrollBackward = (result.firstVisibleItem?.index ?: 0) != 0 ||
result.firstVisibleItemScrollOffset != 0
overScrollController.refreshContainerInfo(
Size(
result.width.toFloat() + horizontalPadding.roundToPx(),
result.height.toFloat() + verticalPadding.roundToPx()
),
canScrollForward || canScrollBackward
)
}