_client.DownloadDataAsync(new Uri(url));

_client.DownloadDataCompleted += (sender, e) =>

{

    try

    {

        if (e.Result != null && e.Result.Length > 0 && e.Error == null && e.Cancelled == false)

            using (FileStream fileStream = new FileStream(path + file_name, FileMode.Create))

                fileStream.Write(e.Result, 0, e.Result.Length);

    }

    catch (Exception ex)

    {

        OpenOperator.Error(string.Format("列表页生成任务异常，url：{0}", url), ex);

    }

};