HttpClient MultipartFormDataContent

            var fileStream = new MemoryStream(fileContent);

            var parametersList = new MultipartFormDataContent
            {
                { new StringContent(folderName), "FolderName" },
                { new StringContent(fileName), "FileName" },
                { new StreamContent(fileStream), "FileContent" }
            };

            var responseJson = this.DoPostQuery(parametersList, AppConfig.GetEcmWholesaleUploadFileUrl()).Result;

        public async Task<string> DoPostQuery(MultipartFormDataContent multiForm, string url)
        {
            /*
                MultipartFormDataContent=》multipart/form-data
                FormUrlEncodedContent=》application/x-www-form-urlencoded
                StringContent=》application/json等
                StreamContent=》binary
             */
            var httpClient = new HttpClient();
            var response = await httpClient.PostAsync(url, multiForm);
            string responseJson = await response.Content.ReadAsStringAsync();
            return responseJson;
        }