/// <summary>          /// 使用Post方法获取字符串结果          /// </summary>          /// <param name="url"></param>          /// <param name="formItems">Post表单内容</param>          /// <param name="cookieContainer"></param>          /// <param name="timeOut">默认20秒</param>          /// <param name="encoding">响应内容的编码类型（默认utf-8）</param>          /// <returns></returns>          public static string PostForm(string url, List<FormItemModel> formItems, CookieContainer cookieContainer = null, string refererUrl = null, Encoding encoding = null, int timeOut = 20000)        {                        HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);            #region 初始化请求对象              request.Method = "POST";            request.Timeout = timeOut;            request.Accept = "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8";            request.KeepAlive = true;            request.UserAgent = "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/31.0.1650.57 Safari/537.36";            if (!string.IsNullOrEmpty(refererUrl))                request.Referer = refererUrl;            if (cookieContainer != null)                request.CookieContainer = cookieContainer;            #endregion            string boundary = "----" + DateTime.Now.Ticks.ToString("x");//分隔符              request.ContentType = string.Format("multipart/form-data; boundary={0}", boundary);            //请求流              var postStream = new MemoryStream();            #region 处理Form表单请求内容              //是否用Form上传文件              var formUploadFile = formItems != null && formItems.Count > 0;            if (formUploadFile)            {                //文件数据模板                  string fileFormdataTemplate =                    "\r\n--" + boundary +                    "\r\nContent-Disposition: form-data; name=\"{0}\"; filename=\"{1}\"" +                    "\r\nContent-Type: application/octet-stream" +                    "\r\n\r\n";                //文本数据模板                  string dataFormdataTemplate =                    "\r\n--" + boundary +                    "\r\nContent-Disposition: form-data; name=\"{0}\"" +                    "\r\n\r\n{1}";                foreach (var item in formItems)                {                    string formdata = http://www.mamicode.com/null;                    if (item.IsFile)                    {                        //上传文件                          formdata = http://www.mamicode.com/string.Format(                            fileFormdataTemplate,                            item.Key, //表单键                              item.FileName);                    }                    else                    {                        //上传文本                          formdata = http://www.mamicode.com/string.Format(                            dataFormdataTemplate,                            item.Key,                            item.Value);                    }                    //统一处理                      byte[] formdataBytes = null;                    //第一行不需要换行                      if (postStream.Length == 0)                        formdataBytes = Encoding.UTF8.GetBytes(formdata.Substring(2, formdata.Length - 2));                    else                        formdataBytes = Encoding.UTF8.GetBytes(formdata);                    postStream.Write(formdataBytes, 0, formdataBytes.Length);                    //写入文件内容                      if (item.FileContent != null && item.FileContent.Length > 0)                    {                        using (var stream = item.FileContent)                        {                            byte[] buffer = new byte[1024];                            int bytesRead = 0;                            while ((bytesRead = stream.Read(buffer, 0, buffer.Length)) != 0)                            {                                postStream.Write(buffer, 0, bytesRead);                            }                        }                    }                }                //结尾                  var footer = Encoding.UTF8.GetBytes("\r\n--" + boundary + "--\r\n");                postStream.Write(footer, 0, footer.Length);            }            else            {                request.ContentType = "application/x-www-form-urlencoded";            }            #endregion            request.ContentLength = postStream.Length;            #region 输入二进制流              if (postStream != null)            {                postStream.Position = 0;                //直接写入流                  Stream requestStream = request.GetRequestStream();                byte[] buffer = new byte[1024];                int bytesRead = 0;                while ((bytesRead = postStream.Read(buffer, 0, buffer.Length)) != 0)                {                    requestStream.Write(buffer, 0, bytesRead);                }                ////debug                  //postStream.Seek(0, SeekOrigin.Begin);                  //StreamReader sr = new StreamReader(postStream);                  //var postStr = sr.ReadToEnd();                  postStream.Close();//关闭文件访问              }            #endregion            HttpWebResponse response = (HttpWebResponse)request.GetResponse();            if (cookieContainer != null)            {                response.Cookies = cookieContainer.GetCookies(response.ResponseUri);            }            using (Stream responseStream = response.GetResponseStream())            {                using (StreamReader myStreamReader = new StreamReader(responseStream, encoding ?? Encoding.UTF8))                {                    string retString = myStreamReader.ReadToEnd();                    return retString;                }            }        }

/// <summary>          /// 表单数据项          /// </summary>          public class FormItemModel        {            /// <summary>              /// 表单键，request["key"]              /// </summary>              public string Key { set; get; }            /// <summary>              /// 表单值,上传文件时忽略，request["key"].value              /// </summary>              public string Value { set; get; }            /// <summary>              /// 是否是文件              /// </summary>              public bool IsFile            {                get                {                    if (FileContent == null || FileContent.Length == 0)                        return false;                    if (FileContent != null && FileContent.Length > 0 && string.IsNullOrWhiteSpace(FileName))                        throw new Exception("上传文件时 FileName 属性值不能为空");                    return true;                }            }            /// <summary>              /// 上传的文件名              /// </summary>              public string FileName { set; get; }            /// <summary>              /// 上传的文件内容              /// </summary>              public Stream FileContent { set; get; }        }

var formDatas = new List<Common.FormItemModel>();            formDatas.Add(new Common.FormItemModel()            {                Key = "user_id",                Value = "12546"            });            formDatas.Add(new Common.FormItemModel()            {                Key = "content",                Value = "文本内容"            });            formDatas.Add(new Common.FormItemModel()            {                Key = "visible",                Value = "-1"            });            int index = 1;            foreach (var imgurl in "图片集合")            {                var bitmap = new System.Drawing.Bitmap("c:\\1.jpeg");                MemoryStream ms = new MemoryStream();                bitmap.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);                ms.Position = 0;                formDatas.Add(new Common.FormItemModel()                {                    Key = "pic_" + (index++),                    Value = "",                    FileName = "_b.jpeg",                    FileContent = ms                });            }            string result = Common.PostForm("http://xxxx.com/api/xxxx" , formDatas);