notification.userInfo in storeChanged(_:)

In the storeChanged callback function for the notification that the event store has changed, I was able to retrieve an nsarray with information like "x-apple-eventkit:///Task/p1133". How do I use that information to disover which events or reminders were changed. I found documentation that said to cast the event to an NSManagedObject class, but that doesn't work when I try to do that with a reminder. The cast always fails.