form-data提交

// <summary>
        /// 上传执行 方法
        /// </summary>
        /// <param name="parameter">上传文件请求参数</param>
        public string Execute(UploadParameterType parameter)
        {
            using (MemoryStream memoryStream = new MemoryStream())
            {
                // 1.分界线
                string boundary = string.Format("----{0}", DateTime.Now.Ticks.ToString("x")),        // 分界线可以自定义参数
                    beginBoundary = string.Format("--{0} ", boundary),
                    endBoundary = string.Format(" --{0}-- ", boundary);
                byte[] beginBoundaryBytes = parameter.Encoding.GetBytes(beginBoundary),
                    endBoundaryBytes = parameter.Encoding.GetBytes(endBoundary);
                // 2.组装开始分界线数据体 到内存流中
                memoryStream.Write(beginBoundaryBytes, 0, beginBoundaryBytes.Length);
                // 3.组装 上传文件附加携带的参数 到内存流中
                if (parameter.PostParameters != null && parameter.PostParameters.Count > 0)
                {
                    foreach (KeyValuePair<string, string> keyValuePair in parameter.PostParameters)
                    {
                        string parameterHeaderTemplate = string.Format("Content-Disposition: form-data; name="{0}" {1} {2}", keyValuePair.Key, keyValuePair.Value, beginBoundary);
                        byte[] parameterHeaderBytes = parameter.Encoding.GetBytes(parameterHeaderTemplate);

                        memoryStream.Write(parameterHeaderBytes, 0, parameterHeaderBytes.Length);
                    }
                }
                //// 4.组装文件头数据体 到内存流中
                //string fileHeaderTemplate = string.Format("Content-Disposition: form-data; name="{0}"; filename="{1}" Content-Type: application/octet-stream ", parameter.FileNameKey, parameter.FileNameValue);
                //byte[] fileHeaderBytes = parameter.Encoding.GetBytes(fileHeaderTemplate);
                //memoryStream.Write(fileHeaderBytes, 0, fileHeaderBytes.Length);
                // 5.组装文件流 到内存流中
                byte[] buffer = new byte[1024 * 1024 * 1];
                int size = parameter.UploadStream.Read(buffer, 0, buffer.Length);
                while (size > 0)
                {
                    memoryStream.Write(buffer, 0, size);
                    size = parameter.UploadStream.Read(buffer, 0, buffer.Length);
                }
                // 6.组装结束分界线数据体 到内存流中
                memoryStream.Write(endBoundaryBytes, 0, endBoundaryBytes.Length);
                // 7.获取二进制数据
                byte[] postBytes = memoryStream.ToArray();
                // 8.HttpWebRequest 组装
                HttpWebRequest webRequest = (HttpWebRequest)WebRequest.Create(new Uri(parameter.Url, UriKind.RelativeOrAbsolute));
                webRequest.Method = "POST";
                webRequest.Timeout = 10000;
                webRequest.ContentType = string.Format("multipart/form-data; boundary={0}", boundary);
                webRequest.ContentLength = postBytes.Length;
                if (Regex.IsMatch(parameter.Url, "^https://"))
                {
                    ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls;
                    ServicePointManager.ServerCertificateValidationCallback = CheckValidationResult;
                }
                // 9.写入上传请求数据
                using (Stream requestStream = webRequest.GetRequestStream())
                {
                    requestStream.Write(postBytes, 0, postBytes.Length);
                    requestStream.Close();
                }
                // 10.获取响应
                using (HttpWebResponse webResponse = (HttpWebResponse)webRequest.GetResponse())
                {
                    using (StreamReader reader = new StreamReader(webResponse.GetResponseStream(), parameter.Encoding))
                    {
                        string body = reader.ReadToEnd();
                        reader.Close();
                        return body;
                    }
                }
            }
        }

        static bool CheckValidationResult(object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors errors)
        {
            return true;
        }

public class UploadParameterType
    {
        public Dictionary<string, string> PostParameters = new Dictionary<string, string>();
        public MemoryStream UploadStream = new MemoryStream();
        public string Url = "http://api.longtechcc.com:8081/API/MES/Interface/Connector/CollectEvent/UpLoadCollect";
        public Encoding Encoding = System.Text.Encoding.UTF8;
        public string FileNameKey = "test";
        public string FileNameValue = "test.txt";
    }

--调用

UploadParameterType dd = new UploadParameterType();

            Dictionary<string, string> nv = new Dictionary<string, string>();
            nv.Add("RequestJsonStr", "[{"SN":"(LT)STE - ZCKZQT2.01.0(XLX)A1X2HU2110230001","WorkStationCode":"MartinLaser","SortCode":"1"},{"SN":"(LT)STE - ZCKZQT2.01.0(XLX)A1X2HU2110230002","WorkStationCode":"MartinLaser","SortCode":"2"}]");
            nv.Add("VToken", "74817C6533EFA1D04FF8D34B730F9AF6F57CE0B0ABF6FEB231BA94524A284BB21A5FD21E41775358");
            nv.Add("VOrigin", "TPI");


            dd.PostParameters = nv;
            string test=Execute(dd);

参考网页内容网址：

https://blog.csdn.net/elie_yang/article/details/80710059