swift - 如何从系统函数的完成处理程序闭包中返回？

Question

我知道这行不通，因为 completion handler 在 background Thread 上，但是

where am I supposed do dispatch the main queue or what else do i have to do?

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，因此您应该在方法中传递一个闭包并在切换后立即调用。像这样:

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)
    }

}

然后你将像这样调用这个方法:

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