iOS Swift如何在后台播放音频服务系统声音或音频服务系统声音

extension AppDelegate : UNUserNotificationCenterDelegate {

// Receive displayed notifications for iOS 10 devices.
func userNotificationCenter(_ center: UNUserNotificationCenter,
                            willPresent notification: UNNotification,
                            withCompletionHandler completionHandler: @escaping (UNNotificationPresentationOptions) -> Void) {

    let userInfo = notification.request.content.userInfo

    print("userNotificationCenter-UNNotificationPresentationOptions")
    // With swizzling disabled you must let Messaging know about the message, for Analytics
    Messaging.messaging().appDidReceiveMessage(userInfo)

    if let messageID = userInfo[gcmMessageIDKey] {
        print("Message ID: \(messageID)")
    }

    // Print full message.
    print(userInfo)

    // Change this to your preferred presentation option

//    AudioServicesPlayAlertSound(1016)
      AudioServicesPlaySystemSound(1016)
      completionHandler([.alert,.badge])
    }

如果播放FCM推送前台音频

但在后台没有播放音频

如何玩 AudioServicesPlaySystemSound 或 AudioServicesPlayAlertSound 在后台 已检查功能背景模式

Swift 4,iOS 11