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.

Answer 1

1. Declare a notification name

   extension Notification.Name {
       static let purchaseDidFinish = Notification.Name("purchaseDidFinish")
   }
   

2. 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"]
   }
   

3. 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)