等待完成处理程序完成

本文介绍了等待完成处理程序完成-Swift的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我正在尝试检查是否启用了UserNotifications，如果没有启用，我想发出警报。因此，我有一个 checkAvailability 函数，用于检查多项内容，包括UserNotification授权状态。

I am trying to check if UserNotifications are enabled and if not I want to throw an alert. So I have a function checkAvailability which checks multiple things, including the UserNotification authorization status.

func checkAvailabilty() -> Bool { // // other checking // var isNotificationsEnabled = false UNUserNotificationCenter.current().requestAuthorization(options: [.alert, .sound], completionHandler: { (granted, error) in if granted { isNotificationsEnabled = true } else { isNotificationsEnabled = false } }) } if isNotificationsEnabled { return true } else { // Throw alert: Remind user to activate notifications return false } }

但是完成处理程序被调用为时已晚。该函数已经返回 false ，然后执行清单中的代码。

But the completion handler gets called too late. The function already returned false and after that the code in the colsure executes.

我试图放入整个语句 UNUserNotificationCenter.current（）。requestAuthorization（）在同步分派队列中，但这不起作用。

I tried to put the whole statement UNUserNotificationCenter.current().requestAuthorization() in a synchronous dispatch queue but this didn't work.

另一个方法是从闭包内部返回，但我不知道如何完成该操作。

Another approach would be to return from inside the closure but I have no idea how to accomplish that.

推荐答案

不要等待，为了方便使用枚举，请使用完成处理程序：

Do not wait, use a completion handler, for convenience with an enum:

enum AuthResult { case success(Bool), failure(Error) } func checkAvailabilty(completion: @escaping (AuthResult) -> ()) { // // other checking // UNUserNotificationCenter.current().requestAuthorization(options: [.alert, .sound], completionHandler: { (granted, error) in if error != nil { completion(.failure(error!)) } else { completion(.success(granted)) } }) }

并命名为：

checkAvailabilty { result in switch result { case .success(let granted) : if granted { print("access is granted") } else { print("access is denied") } case .failure(let error): print(error) } }