Firebase iOS推送通知自定义声音不播放？

我在iOS应用程序中使用firebase推送通知服务，该应用程序是使用swift 3开发的。目前我收到通知。但我已经为通知警报配置了自定义声音。当应用程序关闭时，我会得到一个默认的声音，而不是剪切的声音。但我想播放自定义声音。我该怎么做？ 以下是我所做的：

    import UIKit
import UserNotifications
import Firebase
import FirebaseInstanceID
import FirebaseMessaging
import GoogleMaps
import GooglePlaces
import GooglePlacePicker

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate, UNUserNotificationCenterDelegate, MessagingDelegate {

var window: UIWindow?


func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {

    //For FireBase Configs
    let settings: UIUserNotificationSettings =
        UIUserNotificationSettings(types: [.alert, .badge, .sound], categories: nil)
    application.registerUserNotificationSettings(settings)
    application.registerForRemoteNotifications()        
    FirebaseApp.configure()
    //FireBase Configs

    return true
}

func application(_ application: UIApplication,open url: URL,sourceApplication: String?, annotation: Any) -> Bool {
    return FBSDKApplicationDelegate.sharedInstance().application(application,open: url as URL!,sourceApplication: sourceApplication,annotation: annotation)
}

//FireBase Notifications Begins
func application(_ application: UIApplication, didReceiveRemoteNotification userInfo: [AnyHashable: Any],
                 fetchCompletionHandler completionHandler: @escaping (UIBackgroundFetchResult) -> Void) {


    //play alert sound
    utilityHelper.playAudio(fileName: "udio", fileExtenstion: "mp3")
    let json = JSON(userInfo)
    NSLog("Received a Notificat`ion: \(json)")
    completionHandler(UIBackgroundFetchResult.newData)
}

func userNotificationCenter(_ center: UNUserNotificationCenter, willPresent notification: UNNotification, withCompletionHandler completionHandler: @escaping (UNNotificationPresentationOptions) -> Void) {

    NSLog("show notification")
    completionHandler(UNNotificationPresentationOptions.alert)
}


func application(received remoteMessage: MessagingRemoteMessage) {


}
func messaging(_ messaging: Messaging, didRefreshRegistrationToken fcmToken: String) {
    NSLog("Refreshed Firebase registration token: \(fcmToken)")



}


func application(_ application: UIApplication,
                         didRegisterForRemoteNotificationsWithDeviceToken deviceToken: Data) {
    Messaging.messaging().apnsToken = deviceToken as Data

        NSLog("Register FireBase Token.")

}
//FireBase Notifications End





}

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我如何做到这一点，任何帮助都将不胜感激。

我最近发现，在ios 9下的target上，自定义声音播放效果不如在ios 10.0*设备上。

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因此，只需将构建目标设置为>=9或使用iOS>=10.1的设备，现在看来这是一个答案。干得好。作为撰写好答案的提示：搜索文档和类似的内容，以备份您的陈述，表明您在帮助用户方面投入了时间和精力。但一定要先读