Eventkit doesn't always delete events

Question

I am working on an app, that gets a student's school lessons online and saves it to the iPhone's calendar.

Every time the lessons get updated, I want to delete all events from the calendar of the week, and then put in the updated lessons for the whole week.

I got no problems in adding the events, but sometimes the events don't get removed?

dispatch_queue_t queue = dispatch_queue_create("com.xxxxr.xxxxxx.calendar", NULL);
    dispatch_async(queue, ^{
        EKEventStore *eventStore = [[EKEventStore alloc] init];
        [eventStore requestAccessToEntityType:EKEntityTypeEvent completion:^(BOOL granted, NSError *error) {

            if (granted){

                NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
                EKCalendar *calendarIdentifier;

                if ([defaults objectForKey:@"Calendar"] == nil || ![eventStore calendarWithIdentifier:[defaults objectForKey:@"Calendar"]]){
                    // Create Calendar if Needed

                    EKSource *theSource = nil;
                    for (EKSource *source in eventStore.sources) {
                        if (source.sourceType == EKSourceTypeCalDAV && [source.title isEqualToString:@"iCloud"]) {
                            theSource = source;
                            NSLog(@"iCloud Store Source");
                            break;
                        } else {
                            for (EKSource *source in eventStore.sources) {
                                if (source.sourceType == EKSourceTypeLocal) {
                                    theSource = source;
                                    NSLog(@"iPhone Local Store Source");
                                    break;
                                }
                            }
                        }
                    }

                    EKCalendar *cal;
                    cal = [EKCalendar calendarForEntityType:EKEntityTypeEvent eventStore:eventStore];
                    cal.title = @"xxxxxxx";
                    cal.source = theSource;
                    [eventStore saveCalendar:cal commit:YES error:nil];
                    NSString *calendar_id = cal.calendarIdentifier;
                    [defaults setObject:calendar_id forKey:@"Calendar"];
                    calendarIdentifier = cal;

                } else {
                    calendarIdentifier  = [eventStore calendarWithIdentifier:[defaults objectForKey:@"Calendar"]];
                    NSLog(@"Calendar Existed");
                }


                /* NOW TO WHERE THE PROBLEM LIES! */
                /* FIRST DELETE ALL EVENTS OF THIS WEEK */

                NSArray *arrayOfIdentitiesToDelete = [defaults objectForKey:@"eventIdentities"];
                for(NSString *identifierOfEventToDelete in arrayOfIdentitiesToDelete){
                    EKEvent *eventToRemove = [eventStore eventWithIdentifier:identifierOfEventToDelete];
                    NSError *error;
                    [eventStore removeEvent:eventToRemove span:EKSpanThisEvent error:&error];
                }

                /* Then create new events from my 'arrayOfLessons' array */

                NSMutableArray *arrayOfEventIdentities = [[NSMutableArray alloc] init];

                for(int dayAddingToCalendar = 0; dayAddingToCalendar < 5; dayAddingToCalendar++){
                    for(NSArray *arrayOfDayAddingToCalendar in [[arrayOfLessons objectAtIndex:dayAddingToCalendar] objectAtIndex:3]){

                        EKEvent *event  = [EKEvent eventWithEventStore:eventStore];
                        event.calendar  = calendarIdentifier;
                        event.title     = [arrayOfDayAddingToCalendar objectAtIndex:4];
                        event.location  = [arrayOfDayAddingToCalendar objectAtIndex:1];
                        event.notes     = [arrayOfDayAddingToCalendar objectAtIndex:0];
                        event.startDate = [arrayOfDayAddingToCalendar objectAtIndex:12];
                        event.endDate   = [arrayOfDayAddingToCalendar objectAtIndex:13];
                        event.allDay    = NO;

                        [eventStore saveEvent:event span:EKSpanThisEvent error:nil];
                        [arrayOfEventIdentities addObject:event.eventIdentifier];
                    }
                }

                [defaults setObject:arrayOfEventIdentities forKey:@"eventIdentities"];

            } else {
                NSLog(@"Not Granted");
            }
        }];
    });

Answer 1

You are saying:

NSError *error;
[eventStore removeEvent:eventToRemove span:EKSpanThisEvent error:&error];

So you are throwing away error-checking. Don't. Look at the error! That's what it's for. Like this:

NSError *error;
BOOL ok = [eventStore removeEvent:eventToRemove span:EKSpanThisEvent error:&error];
if (!ok)
    NSLog(@"%@", error);