Send and receive messages through NSNotificationCenter in Objective-C

Question

I am attempting to send and receive messages through NSNotificationCenter in Objective-C  However  I haven t been able to find any examples on how to do this  How do you send and receive messages through NSNotificationCenter

User · Answer

This one helped me      Add an observer that will respond to loginComplete   NSNotificationCenter defaultCenter  addObserver self                                               selector  selector showMainMenu                                                     name   loginComplete  object nil        Post a notification to loginComplete   NSNotificationCenter defaultCenter  postNotificationName   loginComplete  object nil        the function specified in the same class where we defined the addObserver -  void showMainMenu  NSNotification   note       NSLog   Received Notification - Someone seems to have logged in         Source  http   www smipple net snippet Sounden Simple 20NSNotificationCenter 20example

User · Answer

There is also the possibility of using blocks   NSOperationQueue  mainQueue    NSOperationQueue mainQueue     NSNotificationCenter defaultCenter        addObserverForName   notificationName        object nil      queue mainQueue      usingBlock   NSNotification  notification                   NSLog   Notification received               NSDictionary  userInfo   notification userInfo                               Apple s documentation

User · Answer

SWIFT 5 1 of selected answer for newbies class TestClass       deinit              If you don t remove yourself as an observer  the Notification Center            will continue to try and send notification objects to the deallocated            object          NotificationCenter default removeObserver self             init             super init               Add this instance of TestClass as an observer of the TestNotification             We tell the notification center to inform us of  quot TestNotification quot             notifications using the receiveTestNotification  selector  By            specifying object nil  we tell the notification center that we are not            interested in who posted the notification  If you provided an actual            object rather than nil  the notification center will only notify you            when the notification was posted by that particular object           NotificationCenter default addObserver self  selector   selector receiveTest       name  NSNotification Name  quot TestNotification quot    object  nil              objc func receiveTest   notification  Notification                 notification name  should always be   quot TestNotification quot             unless you use this method for observation of other notifications            as well           if notification  name isEqual toString   quot TestNotification quot      nil               print  quot Successfully received the test notification  quot                          somewhere else in another class      func someMethod               All instances of TestClass will be notified         NotificationCenter default post name  NSNotification Name rawValue   quot TestNotification quot    object  self

User · Answer

implementation TestClass  -  void  dealloc          If you don t remove yourself as an observer  the Notification Center        will continue to try and send notification objects to the deallocated        object        NSNotificationCenter defaultCenter  removeObserver self        super dealloc      -  id  init       self    super init       if   self  return nil          Add this instance of TestClass as an observer of the TestNotification         We tell the notification center to inform us of  TestNotification         notifications using the receiveTestNotification  selector  By        specifying object nil  we tell the notification center that we are not        interested in who posted the notification  If you provided an actual        object rather than nil  the notification center will only notify you        when the notification was posted by that particular object         NSNotificationCenter defaultCenter  addObserver self         selector  selector receiveTestNotification            name   TestNotification          object nil        return self     -  void  receiveTestNotification  NSNotification    notification           notification name  should always be   TestNotification         unless you use this method for observation of other notifications        as well       if    notification name  isEqualToString   TestNotification            NSLog    Successfully received the test notification         end       somewhere else in another class      -  void  someMethod           All instances of TestClass will be notified       NSNotificationCenter defaultCenter           postNotificationName   TestNotification           object self

User · Answer

To expand upon dreamlax s example    If you want to send data along with the notification  In posting code   NSDictionary  userInfo     NSDictionary dictionaryWithObject myObject forKey   someKey      NSNotificationCenter defaultCenter  postNotificationName                            TestNotification  object nil userInfo userInfo     In observing code   -  void  receiveTestNotification  NSNotification    notification        NSDictionary  userInfo   notification userInfo      MyObject  myObject    userInfo objectForKey   someKey

User · Answer

if you re using NSNotificationCenter for updating your view  don t forget to send it from the main thread by calling dispatch async   dispatch async dispatch get main queue            NSNotificationCenter defaultCenter  postNotificationName   my notification  object nil

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