# ActionEventDefinition Defines an action event interval, and any associated parameters. ``` struct ActionEventDefinition where ActionType : EntityAction ``` ## Overview Start, update, end, and skipped events are raised based on one or more event intervals defined by the action animation. Also see: [`ActionEventType`](/documentation/RealityKit/ActionEventType) ## Topics ### Initializers [`init(startTime: TimeInterval, duration: TimeInterval, parameter: ActionEventDefinition.EventParameterType?)`](/documentation/RealityKit/ActionEventDefinition/init(startTime:duration:parameter:)) Constructs an event definition. ### Instance Properties [`var duration: TimeInterval`](/documentation/RealityKit/ActionEventDefinition/duration) The event interval’s duration. [`var parameter: ActionEventDefinition.EventParameterType?`](/documentation/RealityKit/ActionEventDefinition/parameter) Optional parameter data available to the event handler at the time of the event. [`var startTime: TimeInterval`](/documentation/RealityKit/ActionEventDefinition/startTime) The time at which the event interval starts. ### Type Aliases [`typealias EventParameterType`](/documentation/RealityKit/ActionEventDefinition/EventParameterType) --- 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)