# AnimationStateKey A key for accessing animation state values. ``` protocol AnimationStateKey ``` ## Overview To access animation state from an [`AnimationContext`](/documentation/SwiftUI/AnimationContext) in a custom animation, create an `AnimationStateKey`. For example, the following code creates an animation state key named `PausableState` and sets the value for the required [`defaultValue`](/documentation/SwiftUI/AnimationStateKey/defaultValue) property. The code also defines properties for state values that the custom animation needs when calculating animation values. Keeping the state values in the animation state key makes it more convenient to read and write those values in the implementation of a [`CustomAnimation`](/documentation/SwiftUI/CustomAnimation). ``` private struct PausableState: AnimationStateKey { var paused = false var pauseTime: TimeInterval = 0.0 static var defaultValue: Self { .init() } } ``` To make accessing the value of the animation state key more convenient, define a property for it by extending [`AnimationContext`](/documentation/SwiftUI/AnimationContext): ``` extension AnimationContext { fileprivate var pausableState: PausableState { get { state[PausableState.self] } set { state[PausableState.self] = newValue } } } ``` Then, you can read and write your state in an instance of `CustomAnimation` using the [`AnimationContext`](/documentation/SwiftUI/AnimationContext): ``` struct PausableAnimation: CustomAnimation { let base: Animation func animate(value: V, time: TimeInterval, context: inout AnimationContext) -> V? where V : VectorArithmetic { let paused = context.environment.animationPaused let pausableState = context.pausableState var pauseTime = pausableState.pauseTime if pausableState.paused != paused { pauseTime = time - pauseTime context.pausableState = PausableState(paused: paused, pauseTime: pauseTime) } let effectiveTime = paused ? pauseTime : time - pauseTime let result = base.animate(value: value, time: effectiveTime, context: &context) return result } } ``` ## Topics ### Setting the default value [`static var defaultValue: Self.Value`](/documentation/SwiftUI/AnimationStateKey/defaultValue) The default value for the animation state key. [`associatedtype Value`](/documentation/SwiftUI/AnimationStateKey/Value) The associated type representing the type of the animation state key’s value. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)