ios - 使用 urlsessiondownloadtask 从 url 下载文件后，文件无法打开

Question

当我尝试从 url 下载文件时，文件会被下载并存储在文件夹中。但是当我尝试打开该文件时。该文件似乎已损坏，我无法打开该 pdf 文件。

我已经使用下面提到的代码尝试了所有可能性。但它们都不起作用。任何解决方案提前致谢。

static func downloadFileFromUrl(urlString:String, fileName:String,viewController : UIViewController) {

    // Create destination URL
    if let documentsUrl:URL = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first{
        let destinationFileUrl = documentsUrl.appendingPathComponent("\(fileName)")
        //Create URL to the source file you want to download
        let fileURL = URL(string: urlString)
        let sessionConfig = URLSessionConfiguration.default
        let session = URLSession(configuration: sessionConfig)
        let request = URLRequest(url:fileURL!)
        let task = session.downloadTask(with: request) { (tempLocalUrl, response, error) in
            if let tempLocalUrl = tempLocalUrl, error == nil {
                // Success

                 try? FileManager.default.removeItem(at: destinationFileUrl)
                do {
                    try FileManager.default.copyItem(at: tempLocalUrl, to: destinationFileUrl)
                    do {
                        //Show UIActivityViewController to save the downloaded file
                        let contents  = try FileManager.default.contentsOfDirectory(at: documentsUrl, includingPropertiesForKeys: nil, options: .skipsHiddenFiles)
                        for indexx in 0..<contents.count {
                            if contents[indexx].lastPathComponent == destinationFileUrl.lastPathComponent {
                                let activityViewController = UIActivityViewController(activityItems: [contents[indexx]], applicationActivities: nil)
                                viewController.present(activityViewController, animated: true, completion: nil)
                            }
                        }
                    }
                    catch (let err) {
                        UIApplication.shared.keyWindow?.makeToast(message: err.localizedDescription)
                    }
                } catch (let writeError) {
                    DispatchQueue.main.async(execute: {
                        UIApplication.shared.keyWindow?.makeToast(message: "Error creating a file :- \(writeError.localizedDescription)")
                    })
                }
            } else {
                UIApplication.shared.keyWindow?.makeToast(message: "Error downloading the file")
            }
        }
        task.resume()
    }
}

现在下载后的文件打不开。提到的从 url 下载文件的代码是否有问题

Answer 1

downloadTask方法的CompletionHandler在全局(后台)队列中执行。您必须在主队列中呈现您的 ActivityViewController。

使用以下代码来呈现您的activityViewController:

DispatchQueue.main.async(execute: {
   let activityViewController = UIActivityViewController(activityItems: [contents[indexx]], applicationActivities: nil)
   viewController.present(activityViewController, animated: true, completion: nil)    
})

而不仅仅是

let activityViewController = UIActivityViewController(activityItems: [contents[indexx]], applicationActivities: nil)
viewController.present(activityViewController, animated: true, completion: nil)