how to use the object property of NSNotificationce

Question

Could somebody please show me how to use the object property on NSNotifcationCenter. I want to be able to use it to pass an integer value to my selector method.

This is how I have set up the notification listener in my UI View. Seeing as I want an integer value to be passed I'm not sure what to replace nil with.

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


- (void)receiveEvent:(NSNotification *)notification {
    // handle event
    NSLog(@"got event %@", notification);
}

I dispatch the notification from another class like this. The function is passed a variable named index. It's this value that I want to somehow fire off with the notification.

-(void) disptachFunction:(int) index
{
    int pass= (int)index;

    [[NSNotificationCenter defaultCenter] postNotificationName:@"myevent" object:pass];
    //[[NSNotificationCenter defaultCenter] postNotificationName:<#(NSString *)aName#>   object:<#(id)anObject#>
}

Answer 1

The object parameter represents the sender of the notification, which is usually self.

If you wish to pass along extra information, you need to use the NSNotificationCenter method postNotificationName:object:userInfo:, which takes an arbitrary dictionary of values (that you are free to define). The contents needs to be actual NSObject instances, not an integral type such as an integer, so you need to wrap the integer values with NSNumber objects.

NSDictionary* dict = [NSDictionary dictionaryWithObject:
                         [NSNumber numberWithInt:index]
                      forKey:@"index"];

[[NSNotificationCenter defaultCenter] postNotificationName:@"myevent"
                                      object:self
                                      userInfo:dict];

Answer 2

The object property is not appropriate for that. Instead you want to use the userinfo parameter:

+ (id)notificationWithName:(NSString *)aName 
                    object:(id)anObject 
                  userInfo:(NSDictionary *)userInfo

userInfo is, as you can see, an NSDictionary specifically for sending information along with the notification.

Your dispatchFunction method would instead be something like this:

- (void) disptachFunction:(int) index {
    NSDictionary *userInfo = [NSDictionary dictionaryWithObject:[NSNumber numberWithInt:index] forKey:@"pass"];
   [[NSNotificationCenter defaultCenter] postNotificationName:@"myevent" object:nil userInfo:userInfo];
}

Your receiveEvent method would be something like this:

- (void)receiveEvent:(NSNotification *)notification {
    int pass = [[[notification userInfo] valueForKey:@"pass"] intValue];
}