应用程序处于活动状态时，检查Wifi是否已打开

Question

我有一个应用程序使用Reachability库来检测应用程序处于活动状态时何时打开wifi。我在视图控制器中有以下代码示例。当应用程序变为活动状态时，将加载视图控制器。当我在iPhone上运行此代码时，不会调用选择器方法。这段代码有什么问题，我该如何解决？

let reachability = Reachability.reachabilityForInternetConnection()

override func viewDidLoad() {
    super.viewDidLoad()

    println("view did load")

    NSNotificationCenter.defaultCenter().addObserver(self, selector: "reachabilityChanged:", name:  "ReachabilityChangedNotification", object: reachability)

    reachability.startNotifier()
}

func reachabilityChanged(note: NSNotification) {

    // I don't see this line printed out!!!
    println("selector method called")

    let reachability = note.object as! Reachability

    if reachability.isReachable() {
        println("yay internet is on")

    } else {
        println("internet is off")
    }
}