NSNotificationCenter addObserver in Swift

Question

How do you add an observer in Swift to the default notification center   I m trying to port this line of code that sends a notification when the battery level changes     NSNotificationCenter defaultCenter  addObserver self selector  selector batteryLevelChanged   name UIDeviceBatteryLevelDidChangeNotification object nil

User · Answer

In swift 3  Xcode 8 2 - checking battery state level    Add observer NotificationCenter default addObserver self  selector   selector batteryStateDidChange   name  NSNotification Name UIDeviceBatteryStateDidChange  object  nil       Fired when battery level changes   func batteryStateDidChange notification  NSNotification             perform manipulation here

User · Answer

I m able to do one of the following to successfully use a selector - without annotating anything with  objc   NSNotificationCenter defaultCenter   addObserver self      selector  batteryLevelChanged   as Selector      name  UIDeviceBatteryLevelDidChangeNotification       object nil        OR  let notificationSelector  Selector    batteryLevelChanged    NSNotificationCenter defaultCenter   addObserver self      selector  notificationSelector      name  UIDeviceBatteryLevelDidChangeNotification       object nil        My xcrun version shows Swift 1 2  and this works on Xcode 6 4 and Xcode 7 beta 2  which I thought would be using Swift 2 0     xcrun swift --version  Apple Swift version 1 2  swiftlang-602 0 53 1 clang-602 0 53

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Declare a notification name  extension Notification Name       static let purchaseDidFinish   Notification Name  purchaseDidFinish      You can add observer in two ways   Using Selector  NotificationCenter default addObserver self  selector   selector myFunction   name   purchaseDidFinish  object  nil    objc func myFunction notification  Notification        print notification object          myObject     print notification userInfo           AnyHashable  key     Value       or using block  NotificationCenter default addObserver forName   purchaseDidFinish  object  nil  queue  nil     weak self   notification  in     guard let strongSelf   self else           return            strongSelf myFunction notification  notification     func myFunction notification  Notification        print notification object          myObject     print notification userInfo           AnyHashable  key     Value      Post your notification  NotificationCenter default post name   purchaseDidFinish  object   myObject   userInfo    key    Value          from iOS 9 and OS X 10 11  It is no longer necessary for an   NSNotificationCenter observer to un-register itself when being   deallocated  more info   For a block based implementation you need to do a weak-strong dance if you want to use self inside the block  more info  Block based observers need to be removed more info  let center   NSNotificationCenter defaultCenter   center removeObserver self localeChangeObserver

User · Answer

Pass Data using NSNotificationCenter  You can also pass data using NotificationCentre in swift 3 0 and NSNotificationCenter in swift 2 0   Swift 2 0 Version  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 image   notification userInfo   image   as  UIImage        do something with your image            Swift 3 0 Version  The userInfo now takes  AnyHashable Any   as an argument  which we provide as a dictionary literal in Swift  let imageDataDict  String  UIImage      image   image      post a notification  NotificationCenter default post name  NSNotification Name rawValue   notificationName    object  nil  userInfo  imageDataDict       default  is now a property  not a method call     Register to receive notification in your class NotificationCenter default addObserver self  selector   selector self showSpinningWheel       name  NSNotification Name rawValue   notificationName    object  nil      handle notification func showSpinningWheel   notification  NSNotification       if let image   notification userInfo   image   as  UIImage        do something with your image            Source pass data using NotificationCentre swift 3 0  and NSNotificationCenter swift 2 0

User · Answer

In swift 2 2 - XCode 7 3  we use  selector for NSNotificationCenter   NSNotificationCenter defaultCenter   addObserver self  selector   selector rotate   name  UIDeviceOrientationDidChangeNotification  object  nil

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Swift 3 0 in Xcode 8  Swift 3 0 has replaced many  stringly-typed  APIs with struct  wrapper types   as is the case with NotificationCenter  Notifications are now identified by a struct Notfication Name rather than by String  See the Migrating to Swift 3 guide   Previous usage      Define identifier let notificationIdentifier  String    NotificationIdentifier      Register to receive notification NSNotificationCenter defaultCenter   addObserver self  selector   selector YourClassName methodOfReceivedNotification       name  notificationIdentifier  object  nil      Post a notification NSNotificationCenter defaultCenter   postNotificationName notificationIdentifier  object  nil    New Swift 3 0 usage      Define identifier let notificationName   Notification Name  NotificationIdentifier       Register to receive notification NotificationCenter default addObserver self  selector   selector YourClassName methodOfReceivedNotification   name  notificationName  object  nil      Post notification NotificationCenter default post name  notificationName  object  nil    All of the system notification types are now defined as static constants on Notification Name  i e   UIDeviceBatteryLevelDidChange   UIApplicationDidFinishLaunching   UITextFieldTextDidChange  etc   You can extend Notification Name with your own custom notifications in order to stay consistent with the system notifications      Definition  extension Notification Name       static let yourCustomNotificationName   Notification Name  yourCustomNotificationName         Usage  NotificationCenter default post name   yourCustomNotificationName  object  nil

User · Answer

In Swift 5     Let s say if want to Receive Data from ViewControllerB to   ViewControllerA   ViewControllerA  Receiver   import UIKit  class ViewControllerA  UIViewController         override func viewDidLoad             super viewDidLoad              MARK  - - - - - Code for Passing Data through Notification Observer - - - - -            add observer in controller s  where you want to receive data         NotificationCenter default addObserver self  selector   selector self methodOfReceivedNotification notification     name  Notification Name  NotificationIdentifier    object  nil               MARK  - - - - - Method for receiving Data through Post Notificaiton - - - - -      objc func methodOfReceivedNotification notification  Notification            print  Value of notification      notification object                    ViewControllerB  Sender   import UIKit  class ViewControllerB  UIViewController        override func viewDidLoad             super viewDidLoad              MARK  - - - - - Set data for Passing Data Post Notification - - - - -         let objToBeSent    Test Message from Notification          NotificationCenter default post name  Notification Name  NotificationIdentifier    object  objToBeSent

User · Answer

A nice way of doing this is to use the addObserver forName object queue using   method rather than the addObserver   selector name object   method that is often used from Objective-C code  The advantage of the first variant is that you don t have to use the  objc attribute on your method       func batteryLevelChanged notification  Notification               do something useful with this information            let observer   NotificationCenter default addObserver          forName  NSNotification Name UIDeviceBatteryLevelDidChange          object  nil  queue  nil          using  batteryLevelChanged    and you can even just use a closure instead of a method if you want       let observer   NotificationCenter default addObserver          forName  NSNotification Name UIDeviceBatteryLevelDidChange          object  nil  queue  nil      in print         You can use the returned value to stop listening for the notification later       NotificationCenter default removeObserver observer    There used to be another advantage in using this method  which was that it doesn t require you to use selector strings which couldn t be statically checked by the compiler and so were fragile to breaking if the method is renamed  but Swift 2 2 and later include  selector expressions that fix that problem

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Swift 4 0  amp  Xcode 9 0    Send Post  Notification   NotificationCenter default post name  Notification Name  NotificationIdentifier    object  nil    OR  NotificationCenter default post name  Notification Name  NotificationIdentifier    object  nil  userInfo    Renish   Dadhaniya      Receive Get  Notification   NotificationCenter default addObserver self  selector   selector self methodOfReceivedNotification notification     name  Notification Name  NotificationIdentifier    object  nil    Function-Method handler for received Notification    objc func methodOfReceivedNotification notification  Notification       Swift 3 0  amp  Xcode 8 0    Send Post  Notification   NotificationCenter default post name  Notification Name  NotificationIdentifier    object  nil    Receive Get  Notification   NotificationCenter default addObserver self  selector   selector YourClassName methodOfReceivedNotification notification     name  Notification Name  NotificationIdentifier    object  nil    Method handler for received Notification   func methodOfReceivedNotification notification  Notification         Take Action on Notification     Remove Notification   deinit     NotificationCenter default removeObserver self  name  Notification Name  NotificationIdentifier    object  nil      Swift 2 3  amp  Xcode 7   Send Post  Notification  NSNotificationCenter defaultCenter   postNotificationName  NotificationIdentifier   object  nil    Receive Get  Notification  NSNotificationCenter defaultCenter   addObserver self  selector   selector YourClassName methodOfReceivedNotification       name  NotificationIdentifier   object  nil    Method handler for received Notification  func methodOfReceivedNotification notification  NSNotification        Take Action on Notification         For historic Xcode versions         Send Post  Notification  NSNotificationCenter defaultCenter   postNotificationName  NotificationIdentifier   object  nil    Receive Get  Notification  NSNotificationCenter defaultCenter   addObserver self  selector   methodOfReceivedNotification    name  NotificationIdentifier   object  nil    Remove Notification  NSNotificationCenter defaultCenter   removeObserver self  name   NotificationIdentifier   object  nil  NSNotificationCenter defaultCenter   removeObserver self     Remove from all notifications being observed   Method handler for received Notification  func methodOfReceivedNotification notification  NSNotification         Take Action on Notification     Annotate either the class or the target method with  objc   objc private func methodOfReceivedNotification notification  NSNotification         Take Action on Notification       Or  dynamic private func methodOfReceivedNotification notification  NSNotification         Take Action on Notification

User · Answer

NSNotificationCenter add observer syntax in Swift 4 0 for iOS 11     NotificationCenter default addObserver self  selector   selector keyboardShow   name  NSNotification Name UIKeyboardWillShow  object  nil    This is for keyboardWillShow notification name type  Other type can be selected from the available option   the Selector is of type  objc func which handle how the keyboard will show   this is your user function

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We should remove notification also   Ex   deinit      NotificationCenter default removeObserver self  name NSNotification Name rawValue   notify    object  nil

User · Answer

Swift 5 Notification Observer  override func viewDidLoad         super viewDidLoad        NotificationCenter default addObserver self  selector   selector batteryLevelChanged   name  UIDevice batteryLevelDidChangeNotification  object  nil      objc func batteryLevelChanged notification   NSNotification         do here code    override func viewWillDisappear   animated  Bool        NotificationCenter default removeObserver self  name  UIDevice batteryLevelDidChangeNotification  object  nil

User · Answer

It s the same as the Objective-C API  but uses Swift s syntax   Swift 4 2  amp  Swift 5   NotificationCenter default addObserver      self      selector   selector self batteryLevelChanged       name  UIDevice batteryLevelDidChangeNotification      object  nil    If your observer does not inherit from an Objective-C object  you must prefix your method with  objc in order to use it as a selector    objc private func batteryLevelChanged notification  NSNotification              do stuff using the userInfo property of the notification object     See NSNotificationCenter Class Reference  Interacting with Objective-C APIs

User · Answer

Swift 5  amp  Xcode 10 2   NotificationCenter default addObserver              self              selector   selector batteryLevelDidChangeNotification               name  UIDevice batteryLevelDidChangeNotification              object  nil

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