isOld
A Boolean value that indicates when the observed progress object invokes the publish method before you subscribe to it.
Declaration
var isOld: Bool { get }Discussion
The publish and subscribe mechanism is generally level-triggered, in that when you invoke addSubscriber(forFileURL:withPublishingHandler:), the system invokes your block for every relevant published and unpublished progress object.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 true.
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.