Asp.net web api 如何调用异步任务函数？

我的AllWebApiOperations类代码是

public AllWebApiOperations(string apiURI)
    {
        client = new HttpClient();
        client.BaseAddress = new Uri(apiURI);
        client.DefaultRequestHeaders.Accept.Clear();
        client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
    }

    public async Task<string> GetDataAsync(string route)
    {
        string result= string.Empty;
        HttpResponseMessage response = await client.GetAsync(route);
        if (response.IsSuccessStatusCode)
        {
            result = await response.Content.ReadAsAsync<string>();
        }
        return result;
    }

我的代码web api工作正常，如下所示

但调用函数时出错，如下所示

我不确定为什么会出现此错误，尝试过谷歌搜索，但无法找到解决方案。

找到了答案：

public async Task<string> GetDataAsync(string route)
{
    string result= string.Empty;
    HttpResponseMessage response = await client.GetAsync(route);
    if (response.IsSuccessStatusCode)
    {
        **result = await response.Content.ReadAsAsync<string>();**
    }
    return result;
}

public async Task<string> GetDataAsync(string route)
{
    string result= string.Empty;
    HttpResponseMessage response = await client.GetAsync(route);
    if (response.IsSuccessStatusCode)
    {
        **result = await response.Content.ReadAsAsync<string>();**
    }
    return result;
}

**result = await response.Content.ReadAsStringAsync();**