当应用程序处于非活动状态时（例如在后台播放音乐）如何调用函数？

我正在制作一个音乐流闹钟。音乐在用户选择的持续时间内流动，包括在后台，并且在持续时间结束时，除了本地通知之外，还会播放自定义警报声音。

简而言之 (1) 设置计时器 (2) 本地通知启动 (3) 流媒体音乐停止 (4) 闹钟播放

我可以做到（1）和（2），但我不知道如何做触发器 (3) 或 (4)当应用程序在后台时。

这是（1）和（2）的代码

let center = UNUserNotificationCenter.current()
var trigger : UNNotificationTrigger!
//...
trigger = UNCalendarNotificationTrigger(dateMatching: Calendar.current.dateComponents([.hour, .minute], from: date), repeats: false)

let request = UNNotificationRequest(identifier: UUID().uuidString, content: content, trigger: trigger)
center.add(request)

非常感谢您的帮助。

编辑1：计时器试用。仅当应用程序位于前台时才能使其工作。

if let interval = AppDataManager.shared.wakeupDate?.timeIntervalSince(Date.init()) {
      print("interval ", interval)
      self.wakeUpTimer = Timer.scheduledTimer(withTimeInterval: interval, repeats: false) { (timer) in
        print("Timer Invoked")
        self.stopPlay()
      }
    } else {
      print("interval NOT AVAILABLE")
    }

Edit 2:

print ("Wakeup date set is \(AppDataManager.shared.wakeupDate)")
        print ("Date now is \(Date())")

    let calendar = Calendar.current
    let unitFlags = Set<Calendar.Component>([ .second])
    let datecomponents = calendar.dateComponents(unitFlags, from: Date(), to: AppDataManager.shared.wakeupDate!)
    let seconds = datecomponents.second

    print(String(describing: seconds))
    let secondsInDouble: Double = Double(seconds!)

      let appDelegate = UIApplication.shared.delegate as! AppDelegate
        if appDelegate.globalTimer == nil {
            print ("Timer started")
            appDelegate.globalTimer = Timer.scheduledTimer(withTimeInterval: secondsInDouble, repeats: false, block: {_ in
                NSLog("Right now the music should stop! ????????????????")
                //Function for music stop. This only works in Simulator, or when the app is active in the device
            })
        }