| /* |
| * Copyright 2019 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 |
| |
| /** |
| * Objects implementing this interface are notified when they are initially |
| * used in a composition and when they are no longer being used. |
| * |
| * An object [enters][onEnter] the composition if it is [remember]ed in at least one place in a |
| * composition. Compose may implicitly [remember] an object if doing so is required to restart |
| * the composition later, such as for composable function parameters. An object [leaves][onLeave] |
| * a composition when it is no longer [remember]ed anywhere in that composition. |
| * |
| * Implementations of [CompositionLifecycleObserver] should generally not expose those object |
| * references outside of their immediate usage sites. A [CompositionLifecycleObserver] reference |
| * that is propagated to multiple parts of a composition might remain present in the composition |
| * for longer than expected if it is remembered (explicitly or implicitly) elsewhere in the same |
| * composition, and a [CompositionLifecycleObserver] that appears in more than one composition may |
| * have its lifecycle callback methods called multiple times in no meaningful order and on |
| * multiple threads. Implementations intending to support this use case should implement atomic |
| * reference counting or a similar strategy to correctly manage resources. |
| */ |
| interface CompositionLifecycleObserver { |
| /** |
| * Called when this object successfully enters a composition. |
| * This method is called on the composition's **apply thread.** |
| */ |
| fun onEnter() {} |
| |
| /** |
| * Called when this object leaves a composition. |
| * This method is called on the composition's **apply thread.** |
| */ |
| fun onLeave() {} |
| } |
| |
| /** |
| * Holds an instance of a CompositionLifecycleObserver and a count of how many times it is |
| * used during composition. |
| * |
| * The holder can be used as a key for the identity of the instance. |
| */ |
| internal class CompositionLifecycleObserverHolder(val instance: CompositionLifecycleObserver) { |
| var count: Int = 0 |
| override fun equals(other: Any?): Boolean = |
| other is CompositionLifecycleObserverHolder && instance === other.instance |
| override fun hashCode(): Int = identityHashCode(instance) |
| } |