Swift：使用 URLSession 的“表达式类型不明确，没有更多上下文”

Posted 2023-02-23

【中文标题】Swift：使用 URLSession 的“表达式类型不明确，没有更多上下文”

【英文标题】：Swift: "Type of expression is ambiguous without more context" with URLSession

【发布时间】：2021-06-14 16:12:02

【问题描述】：

我正在尝试在下面实现此代码以在 WKWebView 中捕获 PDF 下载：

func webView(_ webView: WKWebView, decidePolicyFor navigationAction: WKNavigationAction, decisionHandler: @escaping (WKNavigationActionPolicy) -> Void) 
    if let url = navigationAction.request.url 

        print("fileDownload: check ::  \(url)")

        let extention = "\(url)".suffix(4)

        if extention == ".pdf" 
            print("fileDownload: redirect to download events. \(extention)")
            DispatchQueue.main.async 
                self.downloadPDF(tempUrl: "\(url)")
            
            decisionHandler(.cancel)
            return
        

    

    decisionHandler(.allow)


func downloadPDF(tempUrl:String)
    print("fileDownload: downloadPDF")
    guard let url = URL(string: tempUrl) else  return 
    let urlSession = URLSession(configuration: .default, delegate: self, delegateQueue: OperationQueue())
    let downloadTask = urlSession.downloadTask(with: url)
    downloadTask.resume()
    //showHUD(isShowBackground: true); //show progress if you need

func documentInteractionControllerViewControllerForPreview(_ controller: UIDocumentInteractionController) -> UIViewController 
    print("fileDownload: documentInteractionControllerViewControllerForPreview")
    return self

func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didFinishDownloadingTo location: URL) 
    // create destination URL with the original pdf name
    print("fileDownload: urlSession")
    guard let url = downloadTask.originalRequest?.url else  return 
    print("fileDownload: urlSession \(url)")
    let documentsPath = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)[0]
    let destinationURL = documentsPath.appendingPathComponent(url.lastPathComponent)
    // delete original copy
    try? FileManager.default.removeItem(at: destinationURL)
    // copy from temp to Document
    do 
        try FileManager.default.copyItem(at: location, to: destinationURL)
        myViewDocumentsmethod(PdfUrl:destinationURL)
        print("fileDownload: downloadLocation", destinationURL)
        DispatchQueue.main.async 
            NBMaterialToast.showWithText(self.view, text: "Download Completed", duration: NBLunchDuration.long)
        
     catch let error 
        print("fileDownload: error \(error.localizedDescription)")
    
   // dismissHUD(isAnimated: false); //dismiss progress

func myViewDocumentsmethod(PdfUrl:URL)
    print("fileDownload: myViewDocumentsmethod \(PdfUrl)")
    DispatchQueue.main.async 
        let controladorDoc = UIDocumentInteractionController(url: PdfUrl)
        controladorDoc.delegate = self
        controladorDoc.presentPreview(animated: true)
    

正如这个帖子所建议的那样：

Download embedded PDF loaded in WKWebView

但是 Xcode 给了我以下错误：

“没有更多上下文，表达式的类型是模棱两可的”

对于 downloadPDF 函数中的以下行：

let urlSession = URLSession(configuration: .default, delegate: self, delegateQueue: OperationQueue())

如您在随附的屏幕截图中所见。

关于如何解决这个问题的任何想法？

【问题讨论】：

也许从缩小问题的原因开始。如果将 delegate 和/或 delegateQueue 参数更改为 nil，会发生什么？如果您明确配置参数，即URLSessionConfiguration.default，会发生什么？另外，self 的类型是什么，它是如何声明符合URLSessionDelegate 的？

试过了，但问题仍然存在......

【参考方案1】：

继承URLSessionDelegate 协议给你的类。

【讨论】：

是的！就是这样！太愚蠢了，我没想到……非常感谢！