How to Identify Ekevent Uniquely with Sync Across the Devices

How sync events on iOS with EventKit across multiple devices

calendarItemExternalIdentifier is available as soon as you save (with commit) a calendar item. But, there are situations when the calendarItemExternalIdentifier is later changed, when the calendar item is synced further to the server (e.g. if it's an event from an Exchange account).

All the other identifiers are not shared between devices (this includes identifiers for sources and calendars), so the best option is sticking with calendarItemExternalIdentifier.

A full sync with a calendar can occur when the user sets up a new source (e.g. the user removes and adds the same Exchange account). There may also be different situations that cause a full calendar sync.

calendarIdentifier is a local identifier, so it won't be of much use in your case (except if you want to create a workaround for the issue with calendarItemExternalIdentifier changing).

As mentioned earlier, the calendar and source identifiers are not global, so it would be near impossible to know if "Foo" calendar is setup on a different device, or if the "Foo" calendar is the same "Foo" calendar from your other device.

Usually, if you find your Action object on the new device, you can assume that the calendar that it belongs to is the same as the calendar from the different device.

One way to go about it, when updating your Action objects, would be to save the changes (as usual) to the server. Each of the devices (including the one that made the change) would then search for the corresponding calendar item, and update it if it's found.

I'm currently doing something similar, and this is probably what I'll end up doing.

A better alternative (probably more time consuming as well) would be to have the server connect and sync with the external sources (CalDav, Exchange etc.).

EKEvent with eventWithIdentifier on iOS

I am using newEvent.eventIdentifier instead of newEvent.calendarItemIdentifier and so far, using [store eventWithIdentifier:_project.event_identifier], I can retrieve, delete and edit an existing event. you should try.

How to properly identify an ical event

If you are using iOS 6 try calendarItemExternalIdentifier.

This identifier allows you to access the same event or reminder across multiple devices.

I had this problem using core data, iCloud and calendars. I captured the eventIdentifier and saved it to core data on one device BUT when I checked the other device the eventIdentifier had changed on the calendar.

Resolved it by capturing the calendarItemExternalIdentifier instead of the eventIdentifier:
iOS Reference

Capture the calendarItemExternalIdentifier when saving the event:

- (void)eventEditViewController:(EKEventEditViewController *)controller
      didCompleteWithAction:(EKEventEditViewAction)action {
        NSError *error = nil;
        EKEvent *thisEvent = controller.event;
        switch (action) {
            case EKEventEditViewActionCanceled:
                 // Edit action canceled, do nothing.
            break;
            case EKEventEditViewActionSaved:
            {[self.selectedClientSession setEventIdentifier:[thisEvent calendarItemExternalIdentifier]];
            .......

When displaying event in the app, query if an event is one of our "session" events :

// Get the event e.g. from a tableview listing of events today    
   calendarEvent = (EKEvent*)[eventsList2 objectAtIndex:indexPath.row];
// Is this one of our session events? Build a predicate to query our clientSession objects by comparing the identifier we captured with the Event calendarItemExternalIdentifier
   self.sessionPredicate = [NSPredicate predicateWithFormat:@" eventIdentifier = %@ ",[calendarEvent calendarItemExternalIdentifier]
// Get the results
   [self setupFetchedResultsController];
//Check that calendarItemExternalIdentifier has been recorded in our session database  
   NSArray *sessionSet = [self.fetchedResultsController fetchedObjects];
//If no results then this is not a client session
   if (sessionSet.count == 0){
    // Just a regular event to display
   } else{
   //It is a client session - display and allow to do interesting stuff
   }

Setting the URL field of an EKEvent

I'm guessing you're on iOS 5 Beta? EKEvents shouldn't have a URL property pre-5.0

Take a look at EKCalendarItem on the 5.0 SDK. EKEvent is being phased out, and it's superclass changed from NSObject to EKCalendarItem.

EKCalendarItem has the @property(nonatomic, copy) NSURL *URL

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