As mentioned by boltClock, the character you are referring to is actually a colon. The difference between @selector(method) and @selector(method:) is the method signature. The 2nd variant expects a parameter to be passed. @selector(method) would expect the method: -(void)method @selector(method:) would expect the method: -(void)method:(id)someParameter
Send a notification: [[NSNotificationCenter defaultCenter] postNotificationName:@”MyCacheUpdatedNotification” object:self]; Receive it: [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(cacheUpdated:) name:@”MyCacheUpdatedNotification” object:nil]; Act on it: – (void)cacheUpdated:(NSNotification *)notification { [self load]; } And dispose of it: [[NSNotificationCenter defaultCenter] removeObserver:self];
One way to prevent duplicate observers from being added is to explicitly call removeObserver for the target / selector before adding it again. I imagine you can add this as a category method: @interface NSNotificationCenter (UniqueNotif) – (void)addUniqueObserver:(id)observer selector:(SEL)selector name:(NSString *)name object:(id)object { [[NSNotificationCenter defaultCenter] removeObserver:observer name:name object:object]; [[NSNotificationCenter defaultCenter] addObserver:observer selector:selector name:name object:object]; } … Read more
As of iOS 9 (and OS X 10.11), you don’t need to remove observers yourself, if you’re not using block based observers though. The system will do it for you, since it uses zeroing-weak references for observers, where it can. And if you are using block based observers, make sure you capture self weakly using … Read more
The generic answer would be “as soon as you no longer need the notifications”. This is obviously not a satisfying answer. I’d recommend, that you add a call [notificationCenter removeObserver: self] in method dealloc of those classes, which you intend to use as observers, as it is the last chance to unregister an observer cleanly. … Read more
Use a delegate if you want to talk to only one object. For example, a tableView has a delegate – only one object should be responsible for dealing with it. Use notifications if you want to tell everyone that something has happened. For example in low memory situations a notification is sent telling your app … Read more
You’ll have to use the “userInfo” variant and pass a NSDictionary object that contains the messageTotal integer: NSDictionary* userInfo = @{@”total”: @(messageTotal)}; NSNotificationCenter* nc = [NSNotificationCenter defaultCenter]; [nc postNotificationName:@”eRXReceived” object:self userInfo:userInfo]; On the receiving end you can access the userInfo dictionary as follows: -(void) receiveTestNotification:(NSNotification*)notification { if ([notification.name isEqualToString:@”TestNotification”]) { NSDictionary* userInfo = notification.userInfo; NSNumber* … Read more
The rule of thumb here is how many clients would like to be notified of an event. If it’s mainly one object (e.g. to dismiss a view or to act upon a button clicked, or to react to a failed download) then you should use the delegate model. If the event you emit may be … Read more
Swift 2.0 Pass info using userInfo which is a optional Dictionary of type [NSObject : AnyObject]? let imageDataDict:[String: UIImage] = [“image”: image] // Post a notification NSNotificationCenter.defaultCenter().postNotificationName(notificationName, object: nil, userInfo: imageDataDict) // Register to receive notification in your class NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(self.showSpinningWheel(_:)), name: notificationName, object: nil) // handle notification func showSpinningWheel(notification: NSNotification) { if let … Read more