如何通过ios swift（4）中的url链接从服务器中放置的文件中读取数据？

我编写了用于从文件中检索数据或下载该文件并在手机中显示的代码。 但我不明白为什么它不显示数据。 当我打开该文件时，它显示为空白，但它在控制台中打印一些hex代码。

我对这个IOS开发很新，请帮助我。 我想通过链接从服务器检索数据，并在移动设备上显示。 在此先感谢您可以通过其他方式提供帮助。

以下是我的代码

let username = "xxxx" let password = "xyz" let loginData = String(format: "%@:%@", username, password).data(using: String.Encoding.utf8)! let base64LoginData = loginData.base64EncodedString() // create the request let url = URL(string: "http://demo.xyz.com/dctm-rest/repositories/iol_ref2/objects/0900a1848039590d/content-media?format=crtext&modifier=&page=0")! var request = URLRequest(url: url) request.httpMethod = "GET" request.setValue("Basic \(base64LoginData)", forHTTPHeaderField: "Authorization") let session = URLSession.shared let taskk = session.downloadTask(with: request) { (tempLocalUrl, response, error) in if let tempLocalUrl = tempLocalUrl, error == nil { // Success if let statusCode = (response as? HTTPURLResponse)?.statusCode { print("Success: \(statusCode)") } do { let documentsUrl = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first let paths = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true) if paths.count > 0 { documentsDirectory = paths.first! } var fileURL : URL = URL(fileURLWithPath: documentsUrl!.absoluteString+filename) if(mimetype == "text/plain"){ fileURL = URL(fileURLWithPath: documentsUrl!.absoluteString+filename+".txt") }else if(mimetype == "application/pdf"){ fileURL = URL(fileURLWithPath: documentsUrl!.absoluteString+filename+".pdf") } print(fileURL) let dataFromURL = NSData(contentsOf: tempLocalUrl) dataFromURL?.write(to: fileURL, atomically: true) print(dataFromURL) try FileManager.default.copyItem(at: tempLocalUrl, to: fileURL) OperationQueue.main.addOperation { self.activityIndicator.stopAnimating() UIApplication.shared.endIgnoringInteractionEvents() let documentController = UIDocumentInteractionController.init(url: fileURL) documentController.delegate = self as? UIDocumentInteractionControllerDelegate documentController.presentPreview(animated: true) } } catch (let writeError) { print("error writing file : \(writeError)") } } else { print("Failure: %@", error?.localizedDescription); } } taskk.resume()