在 swift 3 中下载文件最多只能完成 24 kb？使用 URLSession

Question

我正在使用这个guide 在 swift 3 中下载文件。我试图通过添加某个循环来操纵它，以便能够下载 n 个文件。它可以工作，但最多只能完成 24 kb。

这是我的代码：

for jsonDict in data{
  var jasonData = Attachment()

  if let data = (jsonDict["url"] as? String) {jasonData.url = data} else { jasonData.url = ""}

  self.beginDownloadFile(jasonData: jasonData)
}

func beginDownloadFile(jasonData: Attachment){
        let identifier = jasonData.customer_id + "/attachment/" + jasonData.patient_guid + "@%E%@" + "/" + jasonData.filename + "@%E%@" + jasonData.customer_id  + "@%E%@" + jasonData.patient_guid

        let backgroundSessionConfiguration = URLSessionConfiguration.background(withIdentifier: identifier)

        backgroundSession = Foundation.URLSession(configuration: backgroundSessionConfiguration, delegate: self, delegateQueue: OperationQueue.main)

        var link = self.constants.PATIENTS_PICTURE_LINK + jasonData.customer_id + "/attachment/" + jasonData.guid + "/" + jasonData.filename
        link = link.replacingOccurrences(of: " ", with: "%20")

        let url = URL(string: link)!

        downloadTask = backgroundSession.downloadTask(with: url)
        downloadTask.resume()
    }

    func urlSession(_ session: URLSession,
                    downloadTask: URLSessionDownloadTask,
                    didFinishDownloadingTo location: URL){
        let string_container = session.configuration.identifier!.components(separatedBy: "@%E%@")

        let folderPath = string_container[0]
        let fileName = string_container[1]
        let customerID = string_container[2]
        let patientGUID = string_container[3]

        print("GUID IS: " + patientGUID)

        let path = NSSearchPathForDirectoriesInDomains(FileManager.SearchPathDirectory.documentDirectory, FileManager.SearchPathDomainMask.userDomainMask, true)
        let documentDirectoryPath:String = path[0]

        let fileManager = FileManager()

        let path1 = documentDirectoryPath.stringByAppendingPathComponent(pathComponent: customerID)
        let path2 = path1.stringByAppendingPathComponent(pathComponent: "attachment")
        let path3 = path2.stringByAppendingPathComponent(pathComponent: patientGUID)

        let destinationURLForFile = URL(fileURLWithPath: path3.appendingFormat(fileName))

        do {
            if !fileManager.fileExists(atPath: path1) {
                try fileManager.createDirectory(atPath: path1, withIntermediateDirectories: false, attributes: nil)
            }
            if !fileManager.fileExists(atPath: path2) {
                try fileManager.createDirectory(atPath: path2, withIntermediateDirectories: false, attributes: nil)
            }

            if !fileManager.fileExists(atPath: path3) {
                try fileManager.createDirectory(atPath: path3, withIntermediateDirectories: false, attributes: nil)
            }

        } catch let error as NSError {
            print("ATTACHMENT ERROR: " + error.localizedDescription);
        }

        if fileManager.fileExists(atPath: destinationURLForFile.path){
            //showFileWithPath(path: destinationURLForFile.path)
            do {
                try fileManager.removeItem(at: destinationURLForFile)
                try fileManager.moveItem(at: location, to: destinationURLForFile)
                //showFileWithPath(path: destinationURLForFile.path)
            }catch{
                print("An error occurred while moving/deleting file to destination url")
            }
        }
        else{
            do {
                try fileManager.moveItem(at: location, to: destinationURLForFile)
                //showFileWithPath(path: destinationURLForFile.path)
            }catch{
                print("An error occurred while moving file to destination url")
            }
        }
    }

结果：

Sample Screenshot

是什么导致它在 24 kb 时停止？是因为循环吗？还是标识符操作？

Answer 1

您声明downloadTask 的代码在哪里？它是实例属性吗？

如果是这样，那么每次循环运行时，您都会丢弃指向 downloadTask 的指针，并且这段代码会运行：

downloadTask = backgroundSession.downloadTask(with: url) downloadTask.resume()

因此，您的任务可能会提前发布。如果是这种情况，那么最后次循环下载应该完成。

另外，24k 是否可能是正确的文件大小？或者可能是静态错误页面的大小？