asp.net mvc路由可选参数不能匹配

Question

写了一个Attribute路由Route("Home/{category?}/{subcategory?}/List")想匹配以下规则
/Home/C1/S1/List , /Home/C1/List , /Home/List

好像只能匹配到第一种情况，可选参数没起作用。 
如若匹配以上怎么用一个路由规则搞定？

public class HomeController : Controller

{

    public IActionResult Index()

    {

        return View();

    }

    [Route("Home/{category?}/{subcategory?}/List")]

    public IActionResult List(Category? category = null, SubCategory? subcategory = null)

    {

        return Content(category.ToString() + "/" + subcategory.ToString());

    }

    [Route("Home/{code}/Detail")]

    public IActionResult Detail(string code)

    {

        return Content(code);

    }

}

public enum Category

{

    C1,

    C2,

    C3,

    C4

}

public enum SubCategory

{

    S1,

    S2,

    S3,

    S4

}

在stackoverflow的提问：asp.net mvc routing with multiple optional parameters did not work

Answer 1

一个路由应该是做不到，使用三个可以[Route("Home/List")] [Route("Home/{category?}/List")] [Route("Home/{category?}/{subcategory?}/List")]