UIAlertView takes a long time to appear when called in a completion block

Question

Part of my app requires calendar access, which requires a call to the EKEventStore method -(void)requestAccessToEntityType:(EKEntityType)entityType comple

Answer 1

[alertView show] is not thread safe, so it is adding its UI change to the queue from which the completion block was dispatched rather than the main queue. I resolved this issue by adding dispatch_async(dispatch_get_main_queue(), ^{}); around the code inside the completion block:

[eventStore requestAccessToEntityType:EKEntityTypeEvent
                           completion:^(BOOL granted, NSError *error) {
                               dispatch_async(dispatch_get_main_queue(), ^{
                                   if (granted) {
                                       [self createCalendarEvent];
                                   } else {
                                       UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"Calendar Access Denied"
                                                                                           message:@"Please enable access in Privacy Settings to use this feature."
                                                                                          delegate:nil
                                                                                 cancelButtonTitle:@"OK"
                                                                                 otherButtonTitles:nil];
                                       [alertView show];
                                   }
                               });
                           }];