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

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)