public class callapi_service
    {
        public static TResult<T> getApiModels<T>(string strMethod, int id)
        {
            string result = string.Empty;
            TResult<T> models;
            string apiUrl = "";

            if (strMethod=="GET")
                //apiUrl += getUrlQueryString(id);
                apiUrl = "http://localhost:19357/api/values/"+id;
            try
            {
                HttpWebRequest request = HttpWebRequest.Create(apiUrl) as HttpWebRequest;
                request.Method = strMethod;
                //request.ContentType = httpContentType;
                //request.Timeout = timeout;
                //request.Headers.Add(keyHeaderAuthorization, getApiToken());

                using (HttpWebResponse response = request.GetResponse() as HttpWebResponse)
                {
                    string strHttpStatus = response.StatusCode.ToString();
                    using (StreamReader sr = new StreamReader(response.GetResponseStream()))
                    {
                        result = sr.ReadToEnd();
                    }
                }
                models = JsonConvert.DeserializeObject<TResult<T>>(result);
            }
            catch (WebException ex)
            {
                models = default(TResult<T>);
                models.rc = 99;
                models.msg = ex.Message;
            }
            catch (Exception ex)
            {
                models = default(TResult<T>);
                models.rc = 99;
                models.msg = ex.Message;
            }
            return models;
        }

        #region TResult
        public class TResult
        {
            /// <summary>
            /// result code
            /// </summary>
            public int rc { get; set; }

            /// <summary>
            /// error message
            /// </summary>
            public string msg { get; set; }
        }
        public class TResult<T> : TResult
        {
            /// <summary>
            /// result code
            /// </summary>
            public int rc { get; set; }

            /// <summary>
            /// error message
            /// </summary>
            public string msg { get; set; }
            public T data { get; set; }

        }
        #endregion
    }

protected void Page_Load(object sender, EventArgs e)
        {
            var result=callapi_service.getApiModels<List<apiModel>>("GET",1);
            gvApprovalList.DataSource = result.data;
            gvApprovalList.DataBind();
        }