如何从HttpWebResponse获取字符串uri

我有一个方法，下载文件，同时保持它的原始名称/扩展名:

public void downloadFile(string urlAddress, string location)
    {
        _fileHasher = new HashFile(_controlsRef);
        using (var downloadClient = new WebClient())
        {
            downloadClient.DownloadFileCompleted += new System.ComponentModel.AsyncCompletedEventHandler(Completed);
            downloadClient.DownloadProgressChanged += new DownloadProgressChangedEventHandler(ProgressChanged);
            WebRequest request = WebRequest.Create(urlAddress);
            WebResponse response = request.GetResponse();
            string contentDisposition = response.Headers["Content-Disposition"];
            const string contentFileNamePortion = "filename=";
            Int32 fileNameStartIndex = contentDisposition.IndexOf(contentFileNamePortion, StringComparison.InvariantCulture) + contentFileNamePortion.Length;
            Int32 originalFileNameLength = contentDisposition.Length - fileNameStartIndex;
            string originalFileName = contentDisposition.Substring(fileNameStartIndex, originalFileNameLength);
            Uri URL = new Uri(urlAddress);
            location += "''" + originalFileName;
            this._location = location;
            _downloadStopWatch.Start();
            try
            {
                downloadClient.DownloadFileAsync(URL, location);
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }                                  
    }

然后我查找了一个方法，只有当硬盘上的文件是旧的文件时才下载文件:

public void DownloadAndReplace(FileSystemInfo sourceFile)
    {
        var requestFile = (HttpWebRequest)WebRequest.Create("");
        requestFile.Method = "HEAD";
        var responseFile = (HttpWebResponse)requestFile.GetResponse();
        if (responseFile.LastModified > sourceFile.LastWriteTime)
        {
           // downloadFile(Here's the problem);
        }
    }

我的问题，我如何正确地调用DownloadAndReplace方法的downloadFile方法?