Question

如何在使用Alamofire重新下载之前检查某个文件是否已经下载？我正在使用suggestedDownloadDestination，因此Alamofire会自动选择文件的名称并将其保存在选择的目录中，例如.CachesDirectory。问题是suggestedDownloadDestination给出的值是DownloadFileDestination类型，只有通过请求NSURL调用它才能返回response，但这样我就不能在不执行请求之前就知道文件路径。

这是我目前使用Alamofire下载文件的代码：

Alamofire.download(.GET, downloadLink, destination: destination).progress {
                    bytesRead, totalBytesRead, totalBytesExpectedToRead in

                    }.response {
                        request, response, data, error in

                        guard error == nil else {
                            return
                        }

                        // This will give me the file path but we're already in a Request!
                        print("\(destination(NSURL(string: "")!, response!))")
                }

我错过了什么？

Answer 1

不确定您是否已将此解决，但您可以在Alamofire.DownloadRequest之上创建一个扩展程序，如：

extension Alamofire.DownloadRequest {
    open class func suggestedDownloadDestination(
        for directory: FileManager.SearchPathDirectory = .documentDirectory,
        in domain: FileManager.SearchPathDomainMask = .userDomainMask,
        with options: DownloadOptions)
        -> DownloadFileDestination
    {
        return { temporaryURL, response in
                let destination = DownloadRequest.suggestedDownloadDestination(for: directory, in: domain)(temporaryURL, response)
            return (destination.destinationURL, options)
        }
    }
}

现在，您可以在options参数中指定是否要覆盖文件：

let destination =  DownloadRequest.suggestedDownloadDestination(for: .cachesDirectory,
                                                                in: .userDomainMask,
                                                                with: [DownloadRequest.DownloadOptions.removePreviousFile])

Answer 2

这是我使用的解决方案

下载文件
检查是否存在，否则返回路径

  func downloadDocumentFile(filePath: String,onDownloadProgress: @escaping(_ progress: Double) -> Void,onError: @escaping(_ errorMessage: String) -> Void,onSuccess: @escaping(_ destinationUrl: URL) -> Void){
        guard let url = URL(string: filePath) else {
            onError("Couldn't create url from passed file path")
            assertionFailure()
            return
        }
        let destination = DownloadRequest.suggestedDownloadDestination(for: .documentDirectory, in: .userDomainMask)
        Alamofire.download(url, to: destination)
            .downloadProgress { (progress) in
                onDownloadProgress(progress.fractionCompleted)
        }
        .responseData(queue: .main) { (response) in
            switch response.result {
            case .success:
                if let destinationUrl = response.destinationURL {
                    onSuccess(destinationUrl)
                }else {
                    onError("Couldn't get destination url")
                    assertionFailure()
                }
            case .failure(let error):
                  // check if file exists before
                if let destinationURL = response.destinationURL {
                    if FileManager.default.fileExists(atPath: destinationURL.path){
                        // File exists, so no need to override it. simply return the path.
                        onSuccess(destinationURL)
                        print()
                    }else {
                        onError(error.localizedDescription)
                        assertionFailure()
                    }
                }else {
                    onError(error.localizedDescription)
                    assertionFailure()
                }
            }

        }
    }

在使用Alamofire + suggestedDownloadDestination下载文件之前，请检查文件是否已存在

2 个答案: