LazyMeasuredItem.kt
/*
* Copyright 2020 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.ui.Alignment
import androidx.compose.ui.layout.Placeable
import androidx.compose.ui.unit.LayoutDirection
/**
* Represents one measured item of the lazy list. It can in fact consist of multiple placeables
* if the user emit multiple layout nodes in the item callback.
*/
internal class LazyMeasuredItem(
override val index: Int,
private val placeables: Array<Placeable>,
private val isVertical: Boolean,
private val horizontalAlignment: Alignment.Horizontal?,
private val verticalAlignment: Alignment.Vertical?,
private val layoutDirection: LayoutDirection,
private val reverseLayout: Boolean,
private val startContentPadding: Int,
private val endContentPadding: Int,
/**
* Extra spacing to be added to [size] aside from the sum of the [placeables] size. It
* is usually representing the spacing after the item.
*/
private val spacing: Int,
override val key: Any
) : LazyListItemInfo {
/**
* Sum of the main axis sizes of all the inner placeables.
*/
override val size: Int
/**
* Sum of the main axis sizes of all the inner placeables and [spacing].
*/
val sizeWithSpacings: Int
/**
* Max of the cross axis sizes of all the inner placeables.
*/
val crossAxisSize: Int
override var offset: Int = 0
private set
init {
var mainAxisSize = 0
var maxCrossAxis = 0
placeables.forEach {
mainAxisSize += if (isVertical) it.height else it.width
maxCrossAxis = maxOf(maxCrossAxis, if (!isVertical) it.height else it.width)
}
size = mainAxisSize
sizeWithSpacings = size + spacing
crossAxisSize = maxCrossAxis
}
/**
* Perform placing for all the inner placeables at [offset] main axis position. [layoutWidth]
* and [layoutHeight] should be provided to not place placeables which are ended up outside of
* the viewport (for example one item consist of 2 placeables, and the first one is not going
* to be visible, so we don't place it as an optimization, but place the second one).
* If [reverseOrder] is true the inner placeables would be placed in the inverted order.
*/
fun place(
scope: Placeable.PlacementScope,
layoutWidth: Int,
layoutHeight: Int,
offset: Int
) = with(scope) {
this@LazyMeasuredItem.offset = offset
val mainAxisLayoutSize = if (isVertical) layoutHeight else layoutWidth
var mainAxisOffset = if (reverseLayout) {
mainAxisLayoutSize - offset - size
} else {
offset
}
var index = if (reverseLayout) placeables.lastIndex else 0
while (if (reverseLayout) index >= 0 else index < placeables.size) {
val it = placeables[index]
if (reverseLayout) index-- else index++
if (isVertical) {
val x = requireNotNull(horizontalAlignment)
.align(it.width, layoutWidth, layoutDirection)
if (mainAxisOffset + it.height > -startContentPadding &&
mainAxisOffset < layoutHeight + endContentPadding
) {
it.placeWithLayer(x, mainAxisOffset)
}
mainAxisOffset += it.height
} else {
val y = requireNotNull(verticalAlignment).align(it.height, layoutHeight)
if (mainAxisOffset + it.width > -startContentPadding &&
mainAxisOffset < layoutWidth + endContentPadding
) {
it.placeRelativeWithLayer(mainAxisOffset, y)
}
mainAxisOffset += it.width
}
}
}
}