Observing External Changes to the Calendar Database

Registering for Notifications

An EKEventStore object posts an EKEventStoreChangedNotification notification whenever it detects changes to the Calendar database. Register for this notification if your app handles event or reminder data.

The following code registers for the EKEventStoreChangedNotification notification, as shown in Listing 5-1.

Listing 5-1  The EKEventStoreChangedNotification notification

[[NSNotificationCenter defaultCenter] addObserver:self

                                         selector:@selector(storeChanged:)

                                             name:EKEventStoreChangedNotification

                                           object:eventStore];

Responding to Notifications

When you receive an EKEventStoreChangedNotification notification, it’s possible that objects you’ve fetched—such as an EKEvent, EKReminder, or EKCalendar, among others—have changed. The effect of these changes depends on whether an event was added, modified, or deleted.

• If an event was added, it does not affect any of your previously fetched events or reminders, but the added event may fall within the date range of events you are displaying to the user.

• If an event was modified or deleted, properties of EKEvent and EKReminder objects representing that event may become out of date.

Because your local data is often invalidated or incomplete when a change occurs in the Calendar database, you should refetch your current date range of events whenever you receive an EKEventStoreChangedNotification notification. If you are currently modifying an event and you do not want to refetch it unless it is absolutely necessary to do so, you can call the refresh method on the event. If the method returns YES, you can continue to use the event; otherwise, you need to refetch it.