nsnotificationcenter

I feel that i don't fully understand difference between KVO and NSNotification... They seem to be so similar... Could you make some example showing when is best to use one method and when the other ? I don't speak about Bind and IB, but i mean add Observer programmatically in my code with NSNotificationCenter or KVO [self.preferenceController addObserver:self forKeyPath:@"color" options:NSKeyValueObservingOptionOld context:@"Color-change" ]; KVO only works on values, NSNotification can be used for value changes but it can be used for anything and can carry a much greater payload. For example,

I am trying to run a function when the keyboard shows and disappears and have the following code: let notificationCenter = NotificationCenter.default notificationCenter.addObserver(self, selector: #selector(ViewController.keyBoardUp(Notification :)), name: NSNotification.Name.UIKeyboardWillShow, object: nil) And the function keyBoardUp below: func keyBoardUp( Notification: NSNotification){ print("HELLO") } However the function doesn't print to the console when the keyboard shows. Help would be greatly appreciated Swift 3: override func viewDidLoad() { super.viewDidLoad() NotificationCenter

I have a situation in which i have to intialize an object everytime when it comes from background to foreground and that should be using the NSNotificationCenter not with appdelegate because iam building a static library so there wont be appdelegate with that so please help me in the same. Have you tried UIApplicationWillEnterForegroundNotification ? The app also posts a UIApplicationWillEnterForegroundNotification notification shortly before calling applicationWillEnterForeground: to give interested objects a chance to respond to the transition. Subscribe to notification: [

I have a piece of code that worked in Swift 2 and I tried using Xcode to update the code to the newest version and I fixed everything except two issues. I have this code : let loginvc: LoginVC = self.storyboard?.instantiateViewController(withIdentifier: "LoginVC") as! LoginVC NotificationCenter.defaultCenter().addObserver(self, selector: #selector(LoginViewController.keyboardWillShow(_:)), name: UIKeyboardWillShowNotification, object: nil) NotificationCenter.defaultCenter().addObserver(self, selector: #selector(LoginViewController.keyboardWillHide(_:)), name: UIKeyboardWillHideNotification,

I need to create two classes and both should be able to send and receive the events through the NSNotificationCenter methods.ie Both should have the sendEvent and receiveEvent methods: @implementation Class A -(void)sendEvent { addObserver:--- name:---- object:--- } -(void)ReceiveEvent { postNotificationName: --- object:--- } @end Same as such another class say ClassB should also be able to send and receive the events. How can it be done? Ideally an object would start observing interesting events as soon as its initialized. So it will register all interesting events with the NotificationCenter

I'm confused on why the observer is never removed in the following code. In my viewDidAppear I have the following: -(void)viewDidAppear:(BOOL)animated{ id gpsObserver = [[NSNotificationCenter defaultCenter] addObserverForName:FI_NOTES[kNotificationsGPSUpdated] object:nil queue:[NSOperationQueue mainQueue] usingBlock:^(NSNotification *note){ NSLog(@"run once, and only once!"); [[NSNotificationCenter defaultCenter] removeObserver:gpsObserver]; }]; } The observer never gets removed and the statement is output every time the notification is sent out. Can anyone provide any guidance? When the block