Work With KVO In Swift Ios.Iphone

class CarObserver: NSObject {

  private var kvoContext: UInt8 = 1

  private let car: Car

  init(_ car: Car) {
    self.car = car
    super.init()
    car.addObserver(self, forKeyPath: "miles",
       options: NSKeyValueObservingOptions.New, context: &kvoContext)
  }

  override func observeValueForKeyPath(keyPath: String,
       ofObject object: AnyObject, change: [NSObject : AnyObject],
       context: UnsafeMutablePointer<Void>) {
    if context == &kvoContext {
      println("Change at keyPath = \(keyPath) for \(object)")
    }
  }

  deinit {
    car.removeObserver(self, forKeyPath: "miles")
  }
}