OnPositionedDispatcher.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.ui.node
import androidx.compose.runtime.collection.ExperimentalCollectionApi
import androidx.compose.runtime.collection.mutableVectorOf
import androidx.compose.ui.util.identityHashCode
/**
* Tracks the nodes being positioned and dispatches OnPositioned callbacks when we finished
* the measure/layout pass.
*/
@OptIn(ExperimentalLayoutNodeApi::class, ExperimentalCollectionApi::class)
internal class OnPositionedDispatcher {
private val layoutNodes = mutableVectorOf<LayoutNode>()
fun onNodePositioned(node: LayoutNode) {
layoutNodes += node
node.needsOnPositionedDispatch = true
}
fun onRootNodePositioned(rootNode: LayoutNode) {
layoutNodes.clear()
layoutNodes += rootNode
rootNode.needsOnPositionedDispatch = true
}
fun dispatch() {
// sort layoutNodes so that the root is at the end and leaves are at the front
layoutNodes.sortWith(DepthComparator)
layoutNodes.forEachReversed { layoutNode ->
if (layoutNode.needsOnPositionedDispatch) {
dispatchHierarchy(layoutNode)
}
}
layoutNodes.clear()
}
private fun dispatchHierarchy(layoutNode: LayoutNode) {
layoutNode.dispatchOnPositionedCallbacks()
layoutNode.needsOnPositionedDispatch = false
layoutNode._children.forEach { child ->
dispatchHierarchy(child)
}
}
internal companion object {
private object DepthComparator : Comparator<LayoutNode> {
override fun compare(a: LayoutNode, b: LayoutNode): Int {
val depthDiff = b.depth.compareTo(a.depth)
if (depthDiff != 0) {
return depthDiff
}
return a.identityHashCode().compareTo(b.identityHashCode())
}
}
}
}