swift之将 KVO 添加到设置包

我试图将 KVO 添加到我的 NSUserDefaults 以观察设置中值的变化。我在我的 observeValueForKeyPath:object:change:context 方法中添加了一个断点，但它从未被调用。

这是我的代码:

override init() { 
    super.init() 
 
    NSUserDefaults.standardUserDefaults().addObserver(self, forKeyPath: UserWantsUbiquityPreferenceKey, options: NSKeyValueObservingOptions.New, context: nil) 
} 
 
override func observeValueForKeyPath(keyPath: String!, ofObject object: AnyObject!, change: [NSObject : AnyObject]!, context: UnsafeMutablePointer<Void>) { 
    println("\(keyPath) changed to \(object)") 
} 

请您参考如下方法:

以下代码可以帮助您构建 KVO:

import UIKit 
 
//observer's context 
private var defaultsContext = 0 
 
class ViewController: UIViewController { 
 
    let defaults = NSUserDefaults.standardUserDefaults() 
 
 
    @IBAction func changeDefaults(sender: AnyObject) { 
        //Toggle myPref value (true/false) 
        defaults.setBool(!defaults.boolForKey("myPref"), forKey: "myPref") 
        defaults.synchronize() 
    } 
 
    override func viewDidLoad() { 
        super.viewDidLoad() 
 
        //Add observer 
        defaults.addObserver(self, forKeyPath: "myPref", options: NSKeyValueObservingOptions(), context: &defaultsContext) 
    } 
 
    //Observe changes 
    override func observeValueForKeyPath(keyPath: String!, ofObject object: AnyObject!, change: [NSObject : AnyObject]!, context: UnsafeMutablePointer<Void>) { 
        if context == &defaultsContext { 
            seeUpdate() 
        } else { 
            super.observeValueForKeyPath(keyPath, ofObject: object, change: change, context: context) 
        } 
    } 
 
    //React to changes 
    func seeUpdate() { 
        println(defaults.boolForKey("myPref")) 
    } 
 
    deinit { 
        //Remove observer 
        defaults.removeObserver(self, forKeyPath: "myPref", context: &defaultsContext) 
    } 
 
    override func didReceiveMemoryWarning() { 
        super.didReceiveMemoryWarning() 
    } 
 
}