Question

I have the following code:

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

and I have the cmd as:

-(void) cmd: (NSNotification *) notification

in the same UIViewController. On the other UIViewController I have, I did this:

 NSDictionary * userInfo = [NSDictionary dictionaryWithObject:requestUrl forKey:@"requestUrl"];
        [[NSNotificationCenter defaultCenter] postNotificationName:@"cmdAvailable" object:nil userInfo:userInfo];

Why is it not calling my cmd: (NSNotification *) notification method? I checked and that postNotification is getting called.

Answer 1

Shouldn’t it be this?

NSDictionary * userInfo = [NSDictionary dictionaryWithObject:requestUrl forKey:@"requestUrl"];
        [[NSNotificationCenter defaultCenter] postNotificationName:@"cmdAvailable" object:self userInfo:userInfo];

The documentation says this:

- (void)postNotificationName:(NSString *)notificationName object:(id)notificationSender userInfo:(NSDictionary *)userInfo

Parameters

• notificationName:

  The name of the notification.

• notificationSender:

  The object posting the notification.

• userInfo:

  Information about the the notification. May be nil.

So object should be the object posting the notification, which is self

UPDATE

The notification will contain three parts:

– name

– object

– userInfo

The receiver not only know that the message was sent, but what object sent it.