I made a console app to consume a Web API I just made. The console app code does not compile. It gives me the compilation error:

'System.Net.Http.HttpContent' does not contain a definition for
'ReadAsAsync' and no extension method 'ReadAsAsync' accepting a
first argument of type 'System.Net.Http.HttpContent' could be
found (are you missing a using directive or an assembly reference?)

Here's a test method in which this error occurs.

static IEnumerable<Foo> GetAllFoos()
  using (HttpClient client = new HttpClient())
    client.DefaultRequestHeaders.Add("appkey", "myapp_key");

    var response = client.GetAsync("http://localhost:57163/api/foo").Result;

    if (response.IsSuccessStatusCode)
      return response.Content.ReadAsAsync<IEnumerable<Foo>>().Result.ToList();

  return null;

I have used this method and consumed it from an MVC client.