如何解决 EKEventStore 上的 requestAccess(to:completion:) 中的无限循环？

Question

我正在切换 EKAuthorizationStatus 但即使在 requestAuthorisation(to:commit:) 被调用并返回 true 并且没有错误之后 switch 语句仍然匹配 .notDetermined 情况并且其中的递归正在产生无限循环。这让我抓狂！

我试图找出 requestAuthorisation(to:commit:) 是如何工作的，因为我觉得这个问题完全与并发性或其他问题有关，但我找不到任何东西，所以我很难真正理解这种情况。

而且由于我代码中的递归肯定是这个无限循环的一部分，所以我尝试了一种没有递归的方法。但是由于 EKAuthorizationStatus 可能会在我的应用程序对事件存储的调用之间发生变化，我想事先检查它以相应地对所有状态做出反应。因此，我将不得不调用我的方法来切换授权状态和一个请求它的方法，并处理我 class 中的任何错误，出于可读性、安全性和健全性的原因，我不想这样做。

private func confirmAuthorization(for entityType: EKEntityType) throws {
    switch EKEventStore.authorizationStatus(for: entityType) {
    case EKAuthorizationStatus.notDetermined:
        // Request authorisation for the entity type.
        requestAuthorisation(for: entityType)
    
        // Switch again.
        try confirmAuthorization(for: entityType)
        
    case EKAuthorizationStatus.denied:
        print("Access to the event store was denied.")
        throw EventHelperError.authorisationDenied
    
    case EKAuthorizationStatus.restricted:
        print("Access to the event store was restricted.")
        throw EventHelperError.authorisationRestricted
        
    case EKAuthorizationStatus.authorized:
        print("Acces to the event store granted.")
    }
}

private func requestAuthorisation(for entityType: EKEntityType) {
    store.requestAccess(to: entityType) { (granted, error)  in
        if (granted) && (error == nil) {
            DispatchQueue.main.async {
                print("User has granted access to \(String(describing: entityType))") // It's being printed over and over
            }
        } else {
            DispatchQueue.main.async {
                print("User has denied access to \(String(describing: entityType))")
            }
        }
    }
}

我预计该开关会在首次启动时与 .notDetermined 情况相匹配，它将请求授权。因此，当我再次切换状态时，它现在应该匹配 .authorized 或 .denied 等不同的大小写。但实际上它再次匹配 .notDetermined 情况并且一次又一次地授予访问权限。 \ >:[

控制台：

>2019-01-08 12:50:51.314628+0100 EventManager[4452:190572] libMobileGestalt MobileGestalt.c:890: MGIsDeviceOneOfType is not supported on this platform.
>2019-01-08 12:50:54.608391+0100 EventManager[4452:190572] Adding a new event.
>2019-01-08 12:50:54.784684+0100 EventManager[4452:190572] [MC] System group container for systemgroup.com.apple.configurationprofiles path is /Users/***/Library/Developer/CoreSimulator/Devices/********-****-****-****-************/data/Containers/Shared/SystemGroup/systemgroup.com.apple.configurationprofiles
>2019-01-08 12:50:54.785638+0100 EventManager[4452:190572] [MC] Reading from private effective user settings.
>Acces to the event store granted.
>Saved event with identifier: Optional("F8EAC467-9EC2-476C-BF30-45588240A8D0:903EF489-BB52-4A86-917B-DF72494DEA3D")
>2019-01-08 12:51:03.019751+0100 EventManager[4452:190572] Events succsessfully saved.
>User has granted access to EKEntityType
>User has granted access to EKEntityType
>User has granted access to EKEntityType
>[…]
>User has granted access to EKEntityType
>User has granted access to EKEntityType
>User has granted access to EKEntityType
>2019-01-08 12:51:03.291606+0100 EventManager[4452:190572] [Common] _BSMachError: port 26b03; (os/kern) invalid capability (0x14) "Unable to insert COPY_SEND"
>2019-01-08 12:51:03.317800+0100 EventManager[4452:190572] [Common] _BSMachError: port 26b03; (os/kern) invalid capability (0x14) "Unable to insert COPY_SEND"
>User has granted access to EKEntityType
>User has granted access to EKEntityType
>User has granted access to EKEntityType
>[…]
>User has granted access to EKEntityType
>User has granted access to EKEntityType
>User has granted access to EKEntityType
>Acces to the event store granted.
>Preset <EventManager.EventCreationPreset: 0x6000020ca340> needs update.
>Acces to the event store granted.
>Preset <EventManager.EventCreationPreset: 0x6000020ca340> was updated.
>2019-01-08 12:51:03.567071+0100 EventManager[4452:190572] Events succsessfully saved.
>User has granted access to EKEntityType
>User has granted access to EKEntityType
>User has granted access to EKEntityType
>[…]

Answer 1

// Request authorisation for the entity type.
requestAuthorisation(for: entityType)

正在生成一个正在后台线程中执行的闭包。这意味着程序会继续，并且此方法调用的结果将在将来的某个时间点传递。问题是：

// Switch again.
try confirmAuthorization(for: entityType)

之后立即执行 ~ 在主线程上 ~ 并产生另一个后台线程。在调用另一个后台线程等之前，您不必等待这些后台线程完成。在再次调用 confirmAuthorization 之前，您需要重新编写等待 requestAuthorisation 到 return 的逻辑...

Answer 2

requestAuthorisation 异步运行，因此 confirmAuthorization 在授权对话框呈现给用户之前再次被调用。

通常，在这种模式中（希望在异步模式中递归调用某些东西），解决方案是将递归调用移动到异步方法的完成处理程序中。但在这种情况下，用户在获得授权对话框后，要么接受要么拒绝，担心“如果还没有确定怎么办”的状态是没有意义的。因此，最重要的是，在这种情况下不需要或不需要递归。

话虽如此，您显然确实想要将状态返回给调用者。但是错误抛出模式将不起作用，因为您需要处理异步情况（未确定权限且我们需要显示确认对话框）。

所以我建议您始终使用完成处理程序模式：

private func confirmAuthorization(for entityType: EKEntityType, completion: @escaping (EKAuthorizationStatus) -> Void) {
    let status = EKEventStore.authorizationStatus(for: entityType)

    switch status {
    case .notDetermined:
        requestAuthorisation(for: entityType, completion: completion)

    default:
        completion(status)
    }
}

private func requestAuthorisation(for entityType: EKEntityType, completion: @escaping (EKAuthorizationStatus) -> Void) {
    store.requestAccess(to: entityType) { _, _ in
        DispatchQueue.main.async {
            completion(EKEventStore.authorizationStatus(for: entityType))
        }
    }
}

或者，您可以将其简化为一个方法：

private func confirmAuthorization(for entityType: EKEntityType, completion: @escaping (EKAuthorizationStatus) -> Void) {
    let status = EKEventStore.authorizationStatus(for: entityType)

    switch status {
    case .notDetermined:
        store.requestAccess(to: entityType) { _, _ in
            DispatchQueue.main.async {
                completion(EKEventStore.authorizationStatus(for: entityType))
            }
        }

    default:
        completion(status)
    }
}

那么您可以：

confirmAuthorization(for: .event) { status in
    switch status {
    case .authorized:
        // proceed

    default:
        // handle non-authorized process here
    }
}

// But, remember, the above runs asynchronously, so do *not*
// put any code contingent upon the auth status here. You 
// must put code contingent upon authorization inside the above
// completion handler closure.
//

如何解决 EKEventStore 上的 requestAccess(to:completion:) 中的无限循环？

How to resolve an infinite loop in requestAccess(to:completion:) on EKEventStore?

recursion

infinite-loop

eventkit

ekeventstore

swift

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