Observing External Changes to the Calendar Database
It’s possible for another process or app to modify the Calendar database while your app is running. If your app fetches calendar events or reminders, you should register to be notified about changes to the Calendar database. By doing so, you ensure that the calendar and reminder information you display to the user is current.
Registering for Notifications
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
[[NSNotificationCenter defaultCenter] addObserver:self
Responding to Notifications
When you receive an
EKEventStoreChangedNotification notification, it’s possible that objects you’ve fetched—such as an
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
EKReminderobjects representing that event may become out of date.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.