ModifierLocalConsumerEntity.kt
/*
* 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.ui.node
import androidx.compose.runtime.collection.mutableVectorOf
import androidx.compose.ui.modifier.ModifierLocal
import androidx.compose.ui.modifier.ModifierLocalConsumer
import androidx.compose.ui.modifier.ModifierLocalReadScope
internal class ModifierLocalConsumerEntity(
var provider: ModifierLocalProviderEntity,
val modifier: ModifierLocalConsumer
) : () -> Unit, OwnerScope, ModifierLocalReadScope {
private val modifierLocalsRead = mutableVectorOf<ModifierLocal<*>>()
var isAttached = false
private set
override val isValid: Boolean
get() = isAttached
fun attach() {
isAttached = true
notifyConsumerOfChanges()
}
/**
* The attach has been done, but we want to notify changes after the tree is completely applied.
*/
fun attachDelayed() {
isAttached = true
invalidateConsumer()
}
fun detach() {
modifier.onModifierLocalsUpdated(DetachedModifierLocalReadScope)
isAttached = false
}
override val <T> ModifierLocal<T>.current: T
get() {
modifierLocalsRead += this
val provider = provider.findModifierLocalProvider(this)
return if (provider == null) {
defaultFactory()
} else {
// We need a cast because type information is erased.
// When we check for equality of the key it implies that the types are equal too.
@Suppress("UNCHECKED_CAST")
provider.value as T
}
}
fun invalidateConsumersOf(local: ModifierLocal<*>) {
if (local in modifierLocalsRead) {
// Trigger the value to be read again
provider.layoutNode.owner?.registerOnEndApplyChangesListener(this)
}
}
fun notifyConsumerOfChanges() {
// If the node is not attached, we don't notify the consumers.
// Ultimately when the node is attached, this function will be called again.
if (!isAttached) return
modifierLocalsRead.clear()
val snapshotObserver = provider.layoutNode.requireOwner().snapshotObserver
snapshotObserver.observeReads(this, onReadValuesChanged) {
modifier.onModifierLocalsUpdated(this)
}
}
/**
* Called when the modifiers have changed and we don't know what may have happened, so
* the consumer has to be re-run after the tree is configured.
*/
fun invalidateConsumer() {
provider.layoutNode.owner?.registerOnEndApplyChangesListener(this)
}
/**
* The listener for [UiApplier.onEndChanges]. This is called when we need to trigger
* the consumer to update its values.
*/
override fun invoke() {
notifyConsumerOfChanges()
}
companion object {
val onReadValuesChanged: (ModifierLocalConsumerEntity) -> Unit = { node ->
node.notifyConsumerOfChanges()
}
val DetachedModifierLocalReadScope = object : ModifierLocalReadScope {
override val <T> ModifierLocal<T>.current: T
get() = defaultFactory()
}
}
}