NSNotification not being sent when postNotificationName: called

Question

I'm trying to get one instance of using NSNotificationCenter with addObserver and postNotificationName but I can't work out why it won't work.

I have 2 lines to code to add the observer and send the message in 2 different classes

[[NSNotificationCenter defaultCenter]addObserver:self selector:@selector(newEventLoaded:) name:@"Event" object:nil];

and

[[NSNotificationCenter defaultCenter]postNotificationName:@"Event" object:self];

If I set the name to nil it works fine becuase it's just a broadcast, when i try and define a notification name the messages never get through.

Answer 1

Change this:

[[NSNotificationCenter defaultCenter]postNotificationName:@"Event" object:self];

to this:

[[NSNotificationCenter defaultCenter]postNotificationName:@"Event" object:nil];

If your first notification is registered properly, newEventLoaded should be called.

Answer 2

All my code makes use of NSNotifications like so:

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(updateView) name:@"ScanCompleted" object:nil];

[[NSNotificationCenter defaultCenter] postNotificationName:@"ScanCompleted" object:nil];

The first one is registering the notification and the second posting of the notification.

Answer 3

Have you tried any other names but @"Event" and nil? Just to be sure, you could define your event names in one file and include that into both notification registration and sending. For example:

Header file:

extern NSString * const NOTE_myEventName;

Source file:

NSString * const NOTE_myEventName = @"MyEventName";

Registration:

[[NSNotificationCenter defaultCenter]
 addObserver:self
    selector:@selector(handleMyEvent:)
        name:NOTE_myEventName
      object:nil];

Notification sending:

[[NSNotificationCenter defaultCenter]
    postNotificationName:NOTE_myEventName object:nil];