# register(_:) Registers the custom effect. ``` @MainActor @preconcurrency static func register(_ updateHandler: (@MainActor (inout ForceEffectEvent) -> Void)? = nil) ``` ## Parameters `updateHandler` a closure that computes custom forces for rigid bodies. ## Discussion If a handler is specified, the physics system calls the handler and ignores the update function. --- 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)