Why does NSNotificationCenter post cause a" unrecognized selector sent to instance?"

Question

I have an iPad app (XCode 4.6, Storyboards, iOS 6.2) with several classes. In one class, when I finish posting, I post a notification which I expect another class to catch. Not happening!

Here is the code to register the notifications, which I have in AppDelegate.m:

    // add observers for notificaations
[[NSNotificationCenter defaultCenter] addObserver:self
                                         selector:@selector(calendarTapNotification:)
                                             name:@"calendarDateSelected" object:nil ];
[[NSNotificationCenter defaultCenter] addObserver:self
                                         selector:@selector(notificationOfAppointmentMade:)
                                             name:@"appointmentMade" object:nil ];

Here is the code where I post a notification for one of the observers:

if(aDate != nil) { // if user tapped outside of valid date range, aDate will be nil

    [passedData setObject:aDate forKey:@"selectedDate"];

    //  post notification CFGregorianDate has been tapped and pass selected date
    [[NSNotificationCenter defaultCenter] postNotificationName:@"calendarDateSelected" object:self userInfo:passedData];

}

And this is the code where I handle the "calendarTapNotification" notification which never gets called:

- (void) calendarTapNotification:(NSNotification *) notification  {

//  was the calendar tapped?
if ([[notification name] isEqualToString:@"calendarDateSelected"])  {

    //  get the data in the dictiionary
    NSDictionary *dict = [notification userInfo];
    //        NSLog(@"\ndict contents: %@", [dict objectForKey:@"selectedDate"]);  //  this is NSDate class!

    // gets the year, month, and day for selected date
    NSDate *selectedDate = [dict objectForKey:@"selectedDate"];
    //        NSLog(@"\n\ndict-selectedDate: %@", [dict objectForKey:@"selectedDate"]);


    NSCalendar *calendar = [NSCalendar currentCalendar]; // get default calendar
    NSDateComponents *components = [[NSCalendar currentCalendar] components:NSDayCalendarUnit | NSMonthCalendarUnit | NSYearCalendarUnit fromDate: selectedDate];
    //        NSLog(@"\n\ndateFromComponents: %@", components);

    // create start and end of date
    NSDate *startDate = [self beginningOfDay: [calendar dateFromComponents:components]];
    NSDate *endDate = [self endOfDay: [calendar dateFromComponents:components]];
    //        NSLog(@"\nstartDate: %@    endDate: %@", startDate, endDate);

    //  create the predicate
    NSPredicate *predicate =  ([NSPredicate predicateWithFormat:@"((aStartTime > %@) AND (aStartTime <= %@))", startDate, endDate]);

    //  find all appointments with that selected date (AppointmentInfo is NSManagedContext; appointmentInfo is NSArray)
    appointmentInfo = [AppointmentInfo MR_findAllWithPredicate:predicate];

    SingletonAppointments *sharedInstance = [SingletonAppointments sharedInstance];  //  initialize
    //        if(sharedInstance.globalApptList.count > 0)  //  <--------------  TODO
    //            [sharedInstance.globalApptList removeAllObjects];                   //removeAllObjects];  //  clear out the old stuff

    if(appointmentInfo.count > 0)  {
        for (AppointmentInfo *appt in appointmentInfo) {
            sharedInstance.globalApptList = appointmentInfo;  //  move data to sharedInstance
        }
    }
    else  {
        sharedInstance.globalApptList = nil;
    }
    // NSLog(@"\n\nsharedInstance.count: %d", sharedInstance.globalApptList.count);

    //  re-draw the schedule
    [self.subViewData setNeedsDisplay];

}

}

This is the output from the "crash":

2013-04-17 12:58:47.942 saori[11294:c07] -[AppDelegate calendarTapNotification:]: unrecognized selector sent to instance 0x8a25c60 2013-04-17 12:58:47.943 saori[11294:c07] * Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[AppDelegate calendarTapNotification:]: unrecognized selector sent to instance 0x8a25c60' * First throw call stack: (0x2701012 0x19efe7e 0x278c4bd 0x26f0bbc 0x26f094e 0x14b04f9 0x275b0c5 0x26b5efa 0x13e4bb2 0x7de8 0x80eb 0x966cef 0x966f02 0x944d4a 0x936698 0x2b7edf9 0x2b7ead0 0x2676bf5 0x2676962 0x26a7bb6 0x26a6f44 0x26a6e1b 0x2b7d7e3 0x2b7d668 0x933ffc 0x297d 0x28a5 0x1) libc++abi.dylib: terminate called throwing an exception

I have tried everything I know of, read the two Apple docs on NSNotifications and looked at Google and SO and found nothing)

Why doesn't it handler for notification get called? (which I suppose will lead to what is causing the crash).

Answer 1

Make sure you've implemented

calendarTapNotification:
notificationOfAppointmentMade:

in your AppDelegate.