How to pass object with NSNotificationCenter

Question

I am trying to pass an object from my app delegate to a notification receiver in another class   I want to pass integer messageTotal   Right now I have   In Receiver   -  void  receiveTestNotification  NSNotification    notification       if    notification name  isEqualToString   TestNotification            NSLog    Successfully received the test notification        -  void viewDidLoad        super viewDidLoad          NSNotificationCenter defaultCenter  addObserver self selector  selector dismissSheet  name UIApplicationWillResignActiveNotification object nil         NSNotificationCenter defaultCenter  addObserver self selector  selector receiveTestNotification   name   eRXReceived  object nil     In the class that is doing the notification    UIApplication sharedApplication  applicationIconBadgeNumber   messageTotal    NSNotificationCenter defaultCenter  postNotificationName   eRXReceived  object self     But I want to pass the object messageTotal to the other class

User · Answer

Swift 5  func post         NotificationCenter default post name  Notification Name  SomeNotificationName             object  nil           userInfo   key0    value    key1   1234      func addObservers         NotificationCenter default addObserver self           selector   selector someMethod            name  Notification Name  SomeNotificationName             object  nil      objc func someMethod   notification  Notification        let info0   notification userInfo   key0       let info1   notification userInfo   key1       Bonus  that you should definitely do      Replace Notification Name  SomeNotificationName   with  someNotificationName   extension Notification Name       static let someNotificationName   Notification Name  SomeNotificationName       Replace  key0  and  key1  with Notification Key key0 and Notification Key key1   extension Notification     enum Key  String       case key0     case key1         Why should I definitely do this   To avoid costly typo errors  enjoy renaming  enjoy find usage etc

User · Answer

Swift 2 Version  As  Johan Karlsson pointed out    I was doing it wrong  Here s the proper way to send and receive information with NSNotificationCenter  First  we look at the initializer for postNotificationName  init name name  String     object object  AnyObject    userInfo userInfo   NSObject   AnyObject     source We ll be passing our information using the userInfo param  The  NSObject   AnyObject  type is a hold-over from Objective-C  So  in Swift land  all we need to do is pass in a Swift dictionary that has keys that are derived from NSObject and values which can be AnyObject  With that knowledge we create a dictionary which we ll pass into the object parameter   var userInfo    String String     userInfo  quot UserName quot      quot Dan quot   userInfo  quot Something quot      quot Could be any object including a custom Type  quot   Then we pass the dictionary into our object parameter  Sender NSNotificationCenter defaultCenter        postNotificationName  quot myCustomId quot   object  nil  userInfo  userInfo   Receiver Class First we need to make sure our class is observing for the notification override func viewDidLoad         super viewDidLoad        NSNotificationCenter defaultCenter   addObserver self  selector  Selector  quot btnClicked  quot    name   quot myCustomId quot   object  nil             Then we can receive our dictionary  func btnClicked notification  NSNotification       let userInfo    String String     notification userInfo as   String String      let name   userInfo  quot UserName quot      print name

User · Answer

Building on the solution provided I thought it might be helpful to show an example passing your own custom data object  which I ve referenced here as  message  as per question    Class A  sender    YourDataObject  message     YourDataObject alloc  init      set your message properties NSDictionary  dict    NSDictionary dictionaryWithObject message forKey   message      NSNotificationCenter defaultCenter  postNotificationName   NotificationMessageEvent  object nil userInfo dict     Class B  receiver    -  void viewDidLoad        super viewDidLoad         NSNotificationCenter defaultCenter       addObserver self selector  selector triggerAction   name   NotificationMessageEvent  object nil       pragma mark - Notification - void  triggerAction  NSNotification    notification       NSDictionary  dict   notification userInfo      YourDataObject  message    dict valueForKey   message        if  message    nil               do stuff here with your message data

User · Answer

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  total    NSNumber  userInfo   total            NSLog    Successfully received test notification   i   total intValue

User · Answer

Swift 5 1 Custom Object Type     MARK  - NotificationName    Extending notification name to avoid string errors  extension Notification Name       static let yourNotificationName   Notification Name  yourNotificationName          MARK  - CustomObject class YourCustomObject          Any stuffs you would like to set in your custom object as always      init            MARK  - Notification Sender Class class NotificatioSenderClass            Just grab the content of this function and put it to your function responsible for triggering a notification      func postNotification               Note  - This is the important part pass your object instance as object parameter          let yourObjectInstance   YourCustomObject           NotificationCenter default post name   yourNotificationName  object  yourObjectInstance              MARK  -Notification  Receiver class class NotificationReceiverClass  UIViewController          MARK  - ViewController Lifecycle     override func viewDidLoad             super viewDidLoad              Register your notification listener         NotificationCenter default addObserver self  selector   selector didReceiveNotificationWithCustomObject   name   yourNotificationName  object  nil                MARK  - Helpers      objc private func didReceiveNotificationWithCustomObject notification  Notification              Important  - Grab your custom object here by casting the notification object          guard let yourPassedObject   notification object as  YourCustomObject else  return             That s it now you can use your custom object                                       MARK  - Deinit   deinit            Save your memory by releasing notification listener       NotificationCenter default removeObserver self  name   yourNotificationName  object  nil

[objective-c] How to pass object with NSNotificationCenter

Swift 5

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