带有EKEventStoreChanged通知的NotificationCenter多次调用了不同的通知

Question

First of all please note that I am not registered multiple times as observer as described in various other questions.

When I change something in the native calendar application and return back to my app the selector gets called 4-5 times with different notifications.

In viewDidLoad I remove any possible observers and register agian once:

NotificationCenter.default.removeObserver(self)
NotificationCenter.default.addObserver(self, selector: #selector(reloadModelData(notification:)), name: Notification.Name.EKEventStoreChanged, object: nil)

The corresponding method:

@objc private func reloadModelData(notification: NSNotification) {
    debugPrint("method called \(notification)")
}

Leads to this output

"method called NSConcreteNotification 0x170246300 {name = EKEventStoreChangedNotification; object = ; userInfo = {\\n EKEventStoreChangedObjectIDsUserInfoKey = (\\n \\"x-apple-eventkit:///Location/p259707\\",\\n \\"x-apple-eventkit:///Event/p264955\\"\\n );\\n}}" "method called NSConcreteNotification 0x174258840 {name = EKEventStoreChangedNotification; object = ; userInfo = {\\n EKEventStoreChangedObjectIDsUserInfoKey = (\\n \\"x-apple-eventkit:///Location/p259707\\",\\n \\"x-apple-eventkit:///Event/p264955\\"\\n );\\n}}" "method called NSConcreteNotification 0x17024b250 {name = EKEventStoreChangedNotification; object = ; userInfo = {\\n EKEventStoreChangedObjectIDsUserInfoKey = (\\n \\"x-apple-eventkit:///Location/p259707\\",\\n \\"x-apple-eventkit:///Event/p264955\\"\\n );\\n}}" "method called NSConcreteNotification 0x174253b00 {name = EKEventStoreChangedNotification; object = ; userInfo = {\\n EKEventStoreChangedObjectIDsUserInfoKey = (\\n \\"x-apple-eventkit:///Location/p259707\\",\\n \\"x-apple-eventkit:///Event/ p264955\\"\\n );\\n}}"

Does anyone know how fix this. Meaning only receiving one single call of this observer when re-entering the app?

Answer 1

I guess, this is how it works, the calendar sends you notifications for all primitive changes you've made.

The Apple's documentation suggests to check reminders and events you're accessing by calling refresh . If it returns true , there's no need to refetch them. So multiple notifications arriving wouldn't cause much of a problem.

Also I would recommend to subscribe for notifications in viewWillAppear(_:) and unsubscribe in viewDidDisappear(_:) . Of course there might be exceptions, but usually you don't want to handle them when the screen is not active.