SnapshotContextElement.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.runtime.snapshots
import androidx.compose.runtime.ExperimentalComposeApi
import kotlin.coroutines.CoroutineContext
import kotlinx.coroutines.ThreadContextElement
/**
* Return a [SnapshotContextElement] that will [enter][Snapshot.enter] this [Snapshot] whenever
* the associated coroutine is resumed and leave this snapshot when it suspends.
* The snapshot still must be [disposed][Snapshot.dispose] separately when it will no longer
* be used.
*
* @sample androidx.compose.runtime.samples.snapshotAsContextElementSample
*/
@ExperimentalComposeApi
fun Snapshot.asContextElement(): SnapshotContextElement = SnapshotContextElementImpl(this)
/**
* A [CoroutineContext] element that [enters][Snapshot.enter] an associated snapshot
* whenever a coroutine associated with this context is resumed.
*/
@ExperimentalComposeApi
interface SnapshotContextElement : CoroutineContext.Element {
companion object Key : CoroutineContext.Key<SnapshotContextElement>
}
/**
* Implementation of [SnapshotContextElement] that enters a single given snapshot when updating
* the thread context of a resumed coroutine.
*/
@ExperimentalComposeApi
private class SnapshotContextElementImpl(
private val snapshot: Snapshot
) : SnapshotContextElement, ThreadContextElement<Snapshot?> {
override val key: CoroutineContext.Key<*>
get() = SnapshotContextElement
override fun updateThreadContext(context: CoroutineContext): Snapshot? =
snapshot.unsafeEnter()
override fun restoreThreadContext(context: CoroutineContext, oldState: Snapshot?) {
snapshot.unsafeLeave(oldState)
}
}