等待完成处理程序完成-Swift [英] Wait for completion handler to finish - Swift

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)
    }
}

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