What happened to this async task method?

Question

This is just a simple async task, but I always had weird compiler errors. This code is from a web API service in an ASP.NET 4 project created using VS2010.

Even ContinueWith (not generic) returns the task implicitly, but this error still exists.

the code:

public class TestController : ApiController
{
       public Task<HttpResponseMessage> Test()
       {
            string url = "http://www.stackoverflow.com";
            var client = new HttpClient();

            return client.GetAsync(url).ContinueWith<HttpResponseMessage>((request) =>
            {
                // Error 361 'System.Threading.Tasks.Task' does not contain a definition
                // for 'Result' and no extension method 'Result' accepting a first argument
                // of type 'System.Threading.Tasks.Task' could be found
                // (are you missing a using directive or an assembly reference?)
                var response = request.Result;
                response.EnsureSuccessStatusCode();

                // Error 364 Cannot implicitly convert type 'System.Threading.Tasks.Task<System.Net.Http.HttpResponseMessage>' to 'System.Net.Http.HttpResponseMessage'
                return response.Content.ReadAsStringAsync().ContinueWith<HttpResponseMessage>((read) =>
                {
                    return new HttpResponseMessage();
                });
            });
        }
}

Answer 1

Error 364 is absolutely normal because you are returning Task<Task<HttpResponseMessage>>instead Task<HttpResponseMessage>. After fixing the error 361 will also disappear.

So you can Unwrapresult:

public Task<HttpResponseMessage> Test()
{
    string url = "http://www.stackoverflow.com";
    var client = new HttpClient();
    return client.GetAsync(url).ContinueWith(request =>
    {
        var response = request.Result;
        response.EnsureSuccessStatusCode();
        return response.Content.ReadAsStringAsync().ContinueWith(t =>
        {
            var result = new HttpResponseMessage();
            response.CreateContent(t.Result);
            return response;
        });
    }).Unwrap();
}