LazyMeasuredItemProvider.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.layout.Placeable
import androidx.compose.ui.layout.SubcomposeMeasureScope
import androidx.compose.ui.unit.Constraints
/**
* Abstracts away the subcomposition from the measuring logic.
*/
internal class LazyMeasuredItemProvider(
constraints: Constraints,
isVertical: Boolean,
private val scope: SubcomposeMeasureScope,
private val itemsProvider: LazyListItemsProvider,
private val itemContentFactory: LazyListItemContentFactory,
private val measuredItemFactory: MeasuredItemFactory
) {
// the constraints we will measure child with. the main axis is not restricted
private val childConstraints = Constraints(
maxWidth = if (isVertical) constraints.maxWidth else Constraints.Infinity,
maxHeight = if (!isVertical) constraints.maxHeight else Constraints.Infinity
)
/**
* Used to subcompose items of lazy lists. Composed placeables will be measured with the
* correct constraints and wrapped into [LazyMeasuredItem].
* This method can be called only once with each [index] per the measure pass.
*/
fun getAndMeasure(index: DataIndex): LazyMeasuredItem {
val key = itemsProvider.getKey(index.value)
val content = itemContentFactory.getContent(index.value, key)
val measurables = scope.subcompose(key, content)
val placeables = Array(measurables.size) {
measurables[it].measure(childConstraints)
}
return measuredItemFactory.createItem(index, key, placeables)
}
}
// This interface allows to avoid autoboxing on index param
internal fun interface MeasuredItemFactory {
fun createItem(index: DataIndex, key: Any, placeables: Array<Placeable>): LazyMeasuredItem
}