// NOTE: If you don't always include OnDone, OnFail in the method signitures the invoker (e.g. UI) can't handle them. public void Get(int id, Action <User> onDone, Action <object> onFail) { string url = string.Format("http://my.api.com/api/user/{0}", id); FakeHttpClient.Get <User>(url, onDone, onFail); }