VS2015 正式版中为什么没有了函数前面引用提示了？

 HttpClient _httpClient = new HttpClient();
            var clientId = Config.GetValue("AuthUser");
            var clientSecret = Config.GetValue("AuthPass");

            var apiHost = Config.GetValue("ApiHost");
            _httpClient.BaseAddress = new Uri(apiHost);

            var parameters = new Dictionary<string, string>();
            parameters.Add("grant_type", "password");
            parameters.Add("username", account);
            parameters.Add("password", password);

            _httpClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue(
                "Basic", Convert.ToBase64String(Encoding.ASCII.GetBytes(clientId + ":" + clientSecret))
                );

            var response = await _httpClient.PostAsync("/token", new FormUrlEncodedContent(parameters));
            var responseValue = await response.Content.ReadAsStringAsync();
            if (response.StatusCode == System.Net.HttpStatusCode.OK)
            {
                var access_token = JObject.Parse(responseValue)["access_token"].Value<string>();
                return new TokenResult() { Message = "ok", access_token = access_token };
                //return JObject.Parse(responseValue)["access_token"].Value<string>();
            }
            else
            {
                var modelstate = JObject.Parse(responseValue)["ModelState"][0].Value<string>();
                return new TokenResult() { Message = modelstate };
            }

            //string url = Config.GetValue("ApiHost") + "/token";
            ////设置HttpClientHandler的AutomaticDecompression
            //var handler = new HttpClientHandler() { AutomaticDecompression = DecompressionMethods.GZip };
            ////创建HttpClient（注意传入HttpClientHandler）
            //using (var http = new HttpClient(handler))
            //{
            //    //使用FormUrlEncodedContent做HttpContent
            //    var content = new FormUrlEncodedContent(new Dictionary<string, string>()
            //    {
            //        {"grant_type", "password"},//键名必须为空
            //        { "username", account},
            //        {"password", password },
            //     });

            //    //await异步等待回应

            //    var response = await http.PostAsync(url, content);
            //    //确保HTTP成功状态值
            //    response.EnsureSuccessStatusCode();
            //    //await异步读取最后的JSON（注意此时gzip已经被自动解压缩了，因为上面的AutomaticDecompression = DecompressionMethods.GZip）
            //    var responseValue = await response.Content.ReadAsStringAsync();
            //    if (response.StatusCode == System.Net.HttpStatusCode.OK)
            //    {
            //        return JObject.Parse(responseValue)["access_token"].Value<string>();
            //    }
            //    else
            //    {
            //        return string.Empty;
            //    }
            //}