问快速本地通知声音不起作用怎么解决？

EN

let content = UNMutableNotificationContent()
content.title = "Intro to Notifications"
content.subtitle = "Lets code,Talk is cheap"
content.body = "Sample code from WWDC"
content.sound = UNNotificationSound(named: "out.caf")

// content.sound = UNNotificationSound(named: "out.caf")

let trigger = UNTimeIntervalNotificationTrigger.init(timeInterval: 5.0, repeats: false)
let request = UNNotificationRequest(identifier:self.peripheralUUID, content: content, trigger: trigger)

UNUserNotificationCenter.current().delegate = self
UNUserNotificationCenter.current().add(request){(error) in

    if (error != nil){

        print(error?.localizedDescription)
    }
}