# addObserver(for:using:) Registers an observer that runs when a notice of the given type is sent for this stage. ``` func addObserver(for noticeType: Notice.Type, using observer: @escaping (Notice) -> Void) -> USDStage.ObservationToken where Notice : USDStage.Notice ``` ## Discussion Observation continues while the returned token is retained, and ends when the token is released. --- 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)