public static string Api_Post(string postUrl, string postData, WebHeaderCollection header = null,bool isPic=false)
　　　　　{
      Stream outstream = null;
      Stream instream = null;
      StreamReader sr = null;
      HttpWebResponse response = null;
      HttpWebRequest request = null;
      Encoding encoding = Encoding.UTF8;
      byte[] data = encoding.GetBytes(postData);
      // 准备请求...
      try
      {
        // 设置参数
        request = WebRequest.Create(postUrl) as HttpWebRequest;
        CookieContainer cookieContainer = new CookieContainer();
        request.CookieContainer = cookieContainer;
        request.AllowAutoRedirect = true;
        request.Method = "POST";
        request.ContentType = "application/x-www-form-urlencoded";
        if (header != null) request.Headers = header;
        request.ContentLength = data.Length;
        outstream = request.GetRequestStream();
        outstream.Write(data, 0, data.Length);
        outstream.Close();
        //发送请求并获取相应回应数据
        response = request.GetResponse() as HttpWebResponse;
        //直到request.GetResponse()程序才开始向目标网页发送Post请求
        instream = response.GetResponseStream();

        if (isPic)
        {
          byte[] tt = StreamToBytes(instream);//将数据流转为byte[]
          System.IO.File.WriteAllBytes(HttpContext.Current.Server.MapPath("~/WxCode.jpg"), tt);
          WxQRCodeModel model = new WxQRCodeModel();
          model.data = "192.168.1.216:80/WxCode.jpg";
          model.errcode = 0;
          string content = Config.js.Serialize(model);
          string err = string.Empty;
          return content;
        }
        else
        {
          sr = new StreamReader(instream, encoding);
          //返回结果网页（html）代码
          string content = sr.ReadToEnd();
          string err = string.Empty;
          return content;
        }

      }
      catch (Exception ex)
      {
        if (isPic)
        {
          sr = new StreamReader(instream, encoding);
          //返回结果网页（html）代码
          string content = sr.ReadToEnd();
          string err = string.Empty;
          return content;
        }
        else
        {
          string err = ex.Message;
          return string.Empty;
        }
      }
    }

    ///将数据流转为byte[]
    public static byte[] StreamToBytes(Stream stream)
    {
      List<byte> bytes = new List<byte>();
      int temp = stream.ReadByte();
      while (temp != -1)
      {
        bytes.Add((byte)temp);
        temp = stream.ReadByte();
      }
      return bytes.ToArray();
    }