iOS NSUserDefaults Watching the change of values for a single key

Question

I have the following code aiming to catch the event of a NSUserDefaults value changing for a particular key.

 [[NSUserDefaults standardUserDefaults] addObse         


        

Answer 1

Swift 5 Version:

extension UserDefaults {
    @objc dynamic var keyPath: Int {
        return integer(forKey: "keyPath")
    }
}

HINT: make sure the var has exactly the same as the keyPath

and where you use the observer do:

var observer: NSKeyValueObservation?

override func viewDidLoad() {
    super.viewDidLoad()
    observer = UserDefaults.standard.observe(\.keyPath, options: [.initial, .new], changeHandler: { (defaults, change) in
        //Do something
    })
}

deinit {
    observer?.invalidate()
}