swift-kvo-example.swift

//
//  Swift-KVO
//
//  Created by Jim Correia on 6/5/14.
//  Copyright (c) Jim Correia. All rights reserved.
//
//  Update: 6/17/2014
//
//  KVOContext has gone away; use the same idiom you'd use from Objective-C for the context

import Foundation

typealias KVOContext = UInt8
var MyObservationContext = KVOContext()

class Observer: NSObject {
    func startObservingPerson(person: Person) {
        let options = NSKeyValueObservingOptions.New | NSKeyValueObservingOptions.Old
        person.addObserver(self, forKeyPath: "firstName", options: options, context: &MyObservationContext)
        person.addObserver(self, forKeyPath: "lastName", options: options, context: &MyObservationContext)
    }
    
    func stopObservingPerson(person: Person) {
        person.removeObserver(self, forKeyPath: "firstName", context: &MyObservationContext)
        person.removeObserver(self, forKeyPath: "lastName", context: &MyObservationContext)
    }

    override func observeValueForKeyPath(keyPath: String!, ofObject object: AnyObject!, change: NSDictionary!, context: CMutableVoidPointer) {
        switch (keyPath!, context) {
            case("firstName", &MyObservationContext):
                println("First name changed: \(change)")
        
            case("lastName", &MyObservationContext):
                println("Last name changed: \(change)")

            case(_, &MyObservationContext):
                assert(false, "unknown key path")
        
            default:
                super.observeValueForKeyPath(keyPath, ofObject: object, change: change, context: context)
        }
    }
}

class Person: NSObject {
    var firstName: String?
    var lastName: String?
}

let person = Person()

let observer = Observer()

observer.startObservingPerson(person)

person.firstName = "Jim"
person.lastName = "Correia"

observer.stopObservingPerson(person)