swift - 如何从系统函数的完成处理程序闭包内返回？

Question

我知道这不行,因为它completion handler是在一个background Thread但是

我应该在哪里派遣主队列或我还需要做什么？

这是代码:

static func isNotificationNotDetermined() -> Bool{

    var isNotDetermined = false

    UNUserNotificationCenter.current().getNotificationSettings { (notificationSettings) in
        switch notificationSettings.authorizationStatus {
        case .notDetermined:
            isNotDetermined = true

        case .authorized:
            isNotDetermined = false

        case .denied:
            isNotDetermined = false

        }
    }

    return isNotDetermined
}

Answer 1

你不能这样做; getNotificationSettings是异步的,所以你应该在方法中传递一个闭包,并在切换后立即调用.像这样的东西:

static func isNotificationNotDetermined(completion: (Bool) -> Void) {

    UNUserNotificationCenter.current().getNotificationSettings { (notificationSettings) in
        var isNotDetermined = false
        switch notificationSettings.authorizationStatus {
        case .notDetermined:
            isNotDetermined = true

        case .authorized:
            isNotDetermined = false

        case .denied:
            isNotDetermined = false

        }

        // call the completion and pass the result as parameter
        completion(isNotDetermined)
    }

}

然后你将这样调用这个方法:

    YourClass.isNotificationNotDetermined { isNotDetermined in
        // do your stuff
    }