InfiniteAnimationPolicy.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.platform
import androidx.compose.runtime.withFrameNanos
import kotlin.coroutines.CoroutineContext
import kotlin.coroutines.coroutineContext
import androidx.compose.ui.internal.JvmDefaultWithCompatibility
/**
* Provides a policy that will be applied to animations that get their frame time from
* [withInfiniteAnimationFrameNanos][androidx.compose.animation.core.withInfiniteAnimationFrameNanos]
* or
* [withInfiniteAnimationFrameMillis][androidx.compose.animation.core.withInfiniteAnimationFrameMillis]
* This can be used to intervene in infinite animations to make them finite, for example by
* cancelling such coroutines.
*
* By default no policy is installed, except in instrumented tests that use
* [androidx.compose.ui.test.junit4.ComposeTestRule].
*/
@JvmDefaultWithCompatibility
interface InfiniteAnimationPolicy : CoroutineContext.Element {
/**
* Call this to apply the policy on the given suspending [block]. Execution of the block is
* determined by the policy implementation. For example, a test policy could decide not to
* run the block, or trace its execution.
*
* The block is intended to be part of and will therefore be treated as an infinite animation,
* one that after returning from [onInfiniteOperation] will call it again. If the block is
* not part of an infinite animation, the policy will still be applied.
*/
suspend fun <R> onInfiniteOperation(block: suspend () -> R): R
override val key: CoroutineContext.Key<*> get() = Key
companion object Key : CoroutineContext.Key<InfiniteAnimationPolicy>
}
/**
* Like [withFrameNanos], but applies the [InfiniteAnimationPolicy] from the calling
* [CoroutineContext] if there is one.
*
* Note that this is an exact copy of the implementation in the `animation-core` module. We need
* access to it in this module, but other changes are being considered to this API so we don't want
* to go moving APIs around now if we might change them anyway. b/230369229 tracks cleaning up this
* clipboard inheritance.
*/
internal suspend fun <R> withInfiniteAnimationFrameNanos(onFrame: (frameTimeNanos: Long) -> R): R =
when (val policy = coroutineContext[InfiniteAnimationPolicy]) {
null -> withFrameNanos(onFrame)
else -> policy.onInfiniteOperation { withFrameNanos(onFrame) }
}