HttpClient.PostAsynct 发送Json数据

 public async static Task<string> SendRequest(string url, string data)
        {
            var responseJson = "";
            var client = new HttpClient();
            try
            {
                client.Timeout = new TimeSpan(1, 0, 0, 0, 0);
                client.DefaultRequestHeaders.Add("Connection", "Keep-Alive");
                client.DefaultRequestHeaders.Add("Keep-Alive", "timeout=600");
                client.DefaultRequestHeaders.Add("ContentType", "application/json");
                client.DefaultRequestHeaders.Add("Accept", "*/*");
   
               HttpContent content = new StringContent(data);
               content.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue("application/json");
                var Result =await  client.PostAsync(url, content);
                if (Result.StatusCode == System.Net.HttpStatusCode.OK)
                {
                    responseJson = await Result.Content.ReadAsStringAsync();
                }
                else
                {
                    throw new Exception("Request Url is " + url+ " Response is " + Result.StatusCode);
                }
                if (string.IsNullOrEmpty(responseJson))
                {
                    throw new Exception("Request Url is " + url + " Response is " + Result.StatusCode);
                }
            }
            catch (Exception ex)
            {
                throw;
            }
            finally
            {
                client.Dispose();
            }
            return await Task.FromResult(responseJson);
        }