Is it possible for me to get a call back every time an NSPasteboard is updated?

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No, it is not possible for you to get a call back every time an NSPasteboard is updated. However, you can use the NSPasteboardChangedNotification notification to detect changes in the pasteboard. You can register for this notification using the NSNotificationCenter. When the notification is triggered, you can then get the updated contents of the pasteboard using the NSPasteboard class.