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A quick example for how to use Foundation style KVO from Swift. (Official documentation from Apple is forthcoming.)
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// | |
// Swift-KVO | |
// | |
// Created by Jim Correia on 6/5/14. | |
// Copyright (c) 2014-2015 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 | |
// | |
// Update 6/10/2015 | |
// | |
// Updated for Swift 2 | |
// Use dynamic on observable properties | |
import Foundation | |
typealias KVOContext = UInt8 | |
var MyObservationContext = KVOContext() | |
class Observer: NSObject { | |
func startObservingPerson(person: Person) { | |
let options = NSKeyValueObservingOptions([.New, .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: [NSObject : AnyObject]?, context: UnsafeMutablePointer<Void>) { | |
guard keyPath != nil else { | |
super.observeValueForKeyPath(keyPath, ofObject: object, change: change, context: context) | |
return | |
} | |
switch (keyPath!, context) { | |
case("firstName", &MyObservationContext): | |
print("First name changed: \(change)") | |
case("lastName", &MyObservationContext): | |
print("Last name changed: \(change)") | |
case(_, &MyObservationContext): | |
assert(false, "unknown key path") | |
default: | |
super.observeValueForKeyPath(keyPath, ofObject: object, change: change, context: context) | |
} | |
} | |
} | |
class Person: NSObject { | |
dynamic var firstName: String? | |
dynamic var lastName: String? | |
} | |
let person = Person() | |
let observer = Observer() | |
observer.startObservingPerson(person) | |
person.firstName = "Jim" | |
person.lastName = "Correia" | |
observer.stopObservingPerson(person) |
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