编译器错误消耗Web API调用

Question

I need to implement a webapi call into a legacy ASP.Net Web Forms application.
I know not all of the usings are need for this method but they are for other methods on the page i included on the off chance that one of them is causing the problem.

using System;
using System.Collections.Generic;
using System.Configuration;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using Newtonsoft.Json;
using System.Net.Http;
using System.Net.Http.Headers;

private string GetToken(string Username, string IpAddress)
    {
        string result = string.Empty;

        HttpClient client = new HttpClient();

        client.BaseAddress = new Uri(SSOApiUri);
        client.DefaultRequestHeaders.Accept.Clear();
        client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));

        HttpResponseMessage response = client.GetAsync("api/yourcustomobjects").Result;
        if (response.IsSuccessStatusCode)
        {
            ***var data = await response.Content.ReadAsStringAsync();***
            var token = JsonConvert.DeserializeObject<GetSSOTokenResponse>(data);
            result = token.Token;
        }

        return result;
    }

When I try to compile my application I get the following error at the emphisized line:

Error 19 The 'await' operator can only be used within an async method. Consider marking this method with the 'async' modifier and changing its return type to 'Task< string>'.

I am trying to implement a solution similar to the one found in this question but it is failing. I need to call the WebAPI Method, and return part of the result as a string... not a Task< String>

Answer 1

The error is straightforward. You must have an async method to use the await keyword. Your return value will automatically be wrapped in a Task as a result by the compiler. Note that the .Result can be changed to an await as well. Here's the Microsoft documentation on the async/await keywords

private async Task<string> GetToken(string Username, string IpAddress)
{
   string result = string.Empty;

    HttpClient client = new HttpClient();

    client.BaseAddress = new Uri(SSOApiUri);
    client.DefaultRequestHeaders.Accept.Clear();
    client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));

    HttpResponseMessage response = await client.GetAsync("api/yourcustomobjects");
    if (response.IsSuccessStatusCode)
    {
        var data = await response.Content.ReadAsStringAsync();
        var token = JsonConvert.DeserializeObject<GetSSOTokenResponse>(data);
        result = token.Token;
    }

    return result;
}