asp.net mvc路由可选参数不能匹配

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

---

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")]

---

/Home/C1/List 无法确定是Home/{category?}/List还是Home/{subcategory?}/List

可选参数都会放到最后 而且你的Controller方法要对应

http://stackoverflow.com/a/24691984/2586541