---
title: AnimationStateKey
framework: swiftui
role: symbol
role_heading: Protocol
path: swiftui/animationstatekey
---

# AnimationStateKey

A key for accessing animation state values.

## Declaration

```swift
protocol AnimationStateKey
```

## Overview

Overview To access animation state from an 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 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. private struct PausableState<Value: VectorArithmetic>: 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: extension AnimationContext {     fileprivate var pausableState: PausableState<Value> {         get { state[PausableState<Value>.self] }         set { state[PausableState<Value>.self] = newValue }     } } Then, you can read and write your state in an instance of CustomAnimation using the AnimationContext: struct PausableAnimation: CustomAnimation {     let base: Animation

func animate<V>(value: V, time: TimeInterval, context: inout AnimationContext<V>) -> 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

- [defaultValue](swiftui/animationstatekey/defaultvalue.md)
- [Value](swiftui/animationstatekey/value.md)

## See Also

### Creating custom animations

- [CustomAnimation](swiftui/customanimation.md)
- [AnimationContext](swiftui/animationcontext.md)
- [AnimationState](swiftui/animationstate.md)
- [UnitCurve](swiftui/unitcurve.md)
- [Spring](swiftui/spring.md)