Swift – AVAudioPlayer,声音无法正常播放

我在AppDelegate中没有问题来处理通知/创建警报.我的问题涉及声音.实际上,它无法正常播放.

这是我到目前为止：

//...
class AppDelegate: UIResponder,UIApplicationDelegate {

var window: UIWindow?

func application(application: UIApplication,didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
    // Override point for customization after application launch.

    // Notifications permissions
    let types: UIUserNotificationType = UIUserNotificationType.Sound | UIUserNotificationType.Alert
    let settings: UIUserNotificationSettings = UIUserNotificationSettings(forTypes: types,categories: nil)
    application.registerUserNotificationSettings(settings)

    return true
}

func application(application: UIApplication!,didReceiveLocalNotification notification: UILocalNotification!) {
    let state : UIApplicationState = application.applicationState
    var audioPlayer = AVAudioPlayer()

    if (state == UIApplicationState.Active) {
        // Create sound

        var error:NSError?
        var audioPlayer = AVAudioPlayer()

        AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryAmbient,error: nil)
        AVAudioSession.sharedInstance().setActive(true,error: nil)

        let soundURL = NSURL(fileURLWithPath: NSBundle.mainBundle().pathForResource("sound",ofType: "wav")!)

        audioPlayer = AVAudioPlayer(contentsOfURL: soundURL,error: &error)

        if (error != nil) {
            println("There was an error: (error)")
        } else {
            audioPlayer.prepareToPlay()
            audioPlayer.play()
        }

        // Create alert
        let alertController = UIAlertController(title: "Alert title",message: "Alert message.",preferredStyle: .Alert)

        let noAction = UIAlertAction(title: "No",style: .Cancel) { (action) in
            // ...
        }
        let yesAction = UIAlertAction(title: "Yes",style: .Default) { (action) in
            // ...
        }

        alertController.addAction(noAction)
        alertController.addAction(yesAction)

        self.window?.rootViewController?.presentViewController(alertController,animated: true,completion: nil)

    }

}

有了这个,玩家通过这一行：audioPlayer.play()
它的播放时间不到一秒钟.就像它突然被解除分配一样(？).

我试过以下两件事：

>在创建警报之前(或在显示警报之后)将AVAudioPlayer状态切换回非活动状态：AVAudioSession.sharedInstance().setActive(false,error：nil).如果我这样做,声音播放正确.但是,这种方法是一种同步(阻塞)操作,因此它会延迟其他事情(声音在声音后显示).显然不是一个好的解决方案.
>将audioPlayer属性(var audioPlayer = AVAudioPlayer())移动到类级别,就在窗口下(var window：UIWindow？).如果我这样做,声音播放正确,警报也正确显示.

我不明白为什么它会这样.我错过了什么吗？这是解决我问题的正确方法吗？

提前感谢所有能帮助我理解/解决这个问题的人.