如果缺少qualityOFService，则不会调用Cloudkit错误处理

Question

我正在尝试处理Cloudkit错误。我读了这篇文章：CloudKit - full and complete error handling example，但我有几个问题：

1.如果不设置.qualityOFService，为什么错误处理不起作用？正如文章中提到的，设置为.background？.userInitiated是否正确？另外，我是否必须为loadDataAgain()设置它

2.如何使接受错误和另一个参数的错误处理可重用(根据从中调用的视图控制器)？

 @objc func loadData() {
    let predicate = NSPredicate(value: true)
    let query = CKQuery(recordType: myRecordType.type, predicate: predicate)
    query.sortDescriptors = [NSSortDescriptor(key: "creationDate", ascending: false)]
    let queryOperation = CKQueryOperation(query: query)
    queryOperation.resultsLimit = 5
   //if the below line is missing errors will not be handled
    queryOperation.qualityOfService = .userInitiated
    queryOperation.recordFetchedBlock = { item in
        self.array.append(item)
    }
    queryOperation.queryCompletionBlock = { cursor, error in
        if error != nil{
          if let ckerror = error as? CKError {
            if ckerror.code == CKError.requestRateLimited {
                let retryInterval = ckerror.userInfo[CKErrorRetryAfterKey] as? TimeInterval
                DispatchQueue.main.async {
                    Timer.scheduledTimer(timeInterval: retryInterval!, target: self, selector: #selector(self.loadData), userInfo: nil, repeats: false)
                }
            } else if ckerror.code == CKError.zoneBusy {
                let retryInterval = ckerror.userInfo[CKErrorRetryAfterKey] as? TimeInterval
                DispatchQueue.main.async {
                    Timer.scheduledTimer(timeInterval: retryInterval!, target: self, selector: #selector(self.loadData), userInfo: nil, repeats: false)
                }
            } else if ckerror.code == CKError.limitExceeded {
                let retryInterval = ckerror.userInfo[CKErrorRetryAfterKey] as? TimeInterval
                DispatchQueue.main.async {
                    Timer.scheduledTimer(timeInterval: retryInterval!, target: self, selector: #selector(self.loadData), userInfo: nil, repeats: false)
                }
            } else if ckerror.code == CKError.notAuthenticated {
                //present relevant alert with action to reload ViewController
            } else if ckerror.code == CKError.networkFailure {
                //present relevant alert with action to reload ViewController
            } else if ckerror.code == CKError.networkUnavailable {
                //present relevant alert with action to reload ViewController
            } else if ckerror.code == CKError.quotaExceeded {
                //present relevant alert with action to reload ViewController
            } else if ckerror.code == CKError.partialFailure {
                //present relevant alert with action to reload ViewController
            } else if (ckerror.code == CKError.internalError || ckerror.code == CKError.serviceUnavailable) {
                //present relevant alert with action to reload ViewController
            }
        }
        }
        else{
            if cursor != nil {
                self.loadDataAgain(cursor!)
            }
        }
        OperationQueue.main.addOperation {
            self.tableView.reloadData()
        }
}

func loadDataAgain(_ cursor: CKQueryOperation.Cursor) {
    let queryOperation = CKQueryOperation(cursor: cursor)
    queryOperation.resultsLimit = 5

    queryOperation.recordFetchedBlock = { item in
        self.array.append(item)
    }
    queryOperation.queryCompletionBlock = { cursor, error in
        if error != nil{
            //have the same error handling as above
        }
        else{
            if cursor != nil {
                self.loadDataAgain(cursor!)
            }
        }
        OperationQueue.main.addOperation {
            self.tableView.reloadData()
        }
    }
    Database.share.publicDB.add(queryOperation)
}

Answer 1

对于您的第一个问题，请参阅建议未报告错误的this answer以了解较低的服务质量设置：

这是因为系统正在等待更好的网络条件，而如果您设置了.default或.userInitiated，则系统希望得到“实时”响应

如果你看看the docs关于能源效率的内容，苹果似乎证实了这一点，他说

CKOperation是NSOperation类的子类。尽管NSOperation类的默认QoS级别为NSQualityOfServiceBackground，但CKOperation对象的默认QoS级别为NSQualityOfServiceUtility。在这个级别上，当您的应用程序不使用时，网络请求被视为可自由选择的。在iPhones上，启用低功耗模式时，会暂停任意操作。

如果您不需要默认的.utility，则需要为您创建的每个CKOperation显式设置不同的QOS。如果您发现自己经常使用相关操作执行此操作，我建议您查看CKOperationGroup及其default configuration property -如果您在配置中设置了CKOperation，它将覆盖组中任何QOS的默认值。