Swift 5中的并发竞争条件函数

Question

我有下面的代码，它应该返回NotificationCenter的设置，但是当我运行这段代码时，变量notificationSetting什么也不返回。

如何解决这个问题，以便应用程序等待结果？

func getNotificationSetting() -> String{
    var notificationSetting = ""
    
    UNUserNotificationCenter.current().getNotificationSettings { (settings) in
        switch settings.authorizationStatus {
        case .authorized, .provisional:
            notificationSetting = "Authorized"
        case .denied:
            notificationSetting = "Denied"
        case .notDetermined:
            notificationSetting = "NotDetermined"
        @unknown default:
            notificationSetting = "NotDetermined"
        }
    }
    
    return notificationSetting
}

Answer 1

getNotificationSettings异步执行。

func getNotificationSetting(completionHandler: @escaping (String) -> Void) {
    UNUserNotificationCenter.current().getNotificationSettings { (settings) in
        switch settings.authorizationStatus {
        case .authorized, .provisional:
            completionHandler("Authorized")
        case .denied:
            completionHandler("Denied")
        case .notDetermined:
            completionHandler("NotDetermined")
        @unknown default:
            completionHandler("NotDetermined")
        }
    }
}

func getSettings() {
    self.getNotificationSetting(completionHandler: { (notificationSetting) in
        // do what you want
        print(notificationSetting)
    })
}