# isOld A Boolean value that indicates when the observed progress object invokes the publish method before you subscribe to it. ``` var isOld: Bool { get } ``` ## Discussion The publish and subscribe mechanism is generally *level-triggered*, in that when you invoke [`addSubscriber(forFileURL:withPublishingHandler:)`](/documentation/Foundation/Progress/addSubscriber(forFileURL:withPublishingHandler:)), the system invokes your block for every relevant published and unpublished progress object. Sometimes you need to implement *edge-triggered* behavior, in which you do something either exactly when new progress begins or not at all. In the example above, the Dock doesn’t animate file icons when this method returns . There’s no reliable definition of *before* in this case, which involves multiple processes in a preemptively scheduled system. Don’t use this method for anything more important than best efforts at animating. It can be inaccurate due to processes coming and going from unpredictable user actions. --- 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)