DelegatingNode.kt
/*
* Copyright 2022 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.ui.Modifier
/**
* A [Modifier.Node] which is able to delegate work to other [Modifier.Node] instances.
*
* This can be useful to compose multiple node implementations into one.
*
* @sample androidx.compose.ui.samples.DelegatedNodeSample
*
* @see DelegatingNode
*/
abstract class DelegatingNode : Modifier.Node() {
override fun updateCoordinator(coordinator: NodeCoordinator?) {
super.updateCoordinator(coordinator)
forEachDelegate {
it.updateCoordinator(coordinator)
}
}
private var delegate: Modifier.Node? = null
/**
* In order to properly delegate work to another [Modifier.Node], the delegated instance must
* be created and returned inside of a [delegated] call. Doing this will
* ensure that the created node instance follows all of the right lifecycles and is properly
* discoverable in this position of the node tree.
*
* By using [delegated], the [fn] parameter is executed synchronously, and the result is
* returned from this function for immediate use.
*
* This method can be called from within an `init` block, however the returned delegated node
* will not be attached until the delegating node is attached. If [delegated] is called after
* the delegating node is already attached, the returned delegated node will be attached.
*/
fun <T : Modifier.Node> delegated(fn: () -> T): T {
val owner = node
val delegate = fn()
delegate.setAsDelegateTo(owner)
if (isAttached) {
updateCoordinator(owner.coordinator)
delegate.attach()
}
addDelegate(delegate)
return delegate
}
private fun addDelegate(node: Modifier.Node) {
val tail = delegate
if (tail != null) {
node.parent = tail
}
delegate = node
}
private inline fun forEachDelegate(block: (Modifier.Node) -> Unit) {
var node: Modifier.Node? = delegate
while (node != null) {
block(node)
node = node.parent
}
}
override fun attach() {
super.attach()
forEachDelegate {
it.updateCoordinator(coordinator)
it.attach()
}
}
override fun detach() {
forEachDelegate { it.detach() }
super.detach()
}
override fun reset() {
super.reset()
forEachDelegate { it.reset() }
}
}