Optional route parameters and action selection - asp.net-mvc-2

Question

I use the default route definition:
{controller}/{action}/{id}
where id = UrlParameter.Optional. As much as I understand it this means when id is not being part of the URL this route value will not exists in the RouteValues dictionary.
So this also seems perfectly possible (both GET):
public ActionResult Index() { ... } // handle URLs: controller/action
public ActionResult Index(int id) { ... } // handle URLs: controller/action/id
When id is missing the first action would be executed, but when id is present, the second one would execute. Fine, but it doesn't work. It can't resolve actions.
How can I accomplish this?
I'm thinking of writing a custom action method selector attribute like:
[RequiresRouteValue(string valueName)]
This would make it possible to use this kind of action methods. But is this the only way of doing it?
Is there something built-in I can hang on to?

Answer 1

Use either:
[HttpGet]
public ActionResult Index() { ... } // handle URLs: controller/action
[HttpPost]
public ActionResult Index(int id) { ... } // handle URLs: controller/action/id
Or just have one with a nullable param:
public ActionResult Index(int? id) { ... } // handles both instances
EDIT:
Would something like this work?
routes.MapRoute(
"Default", // Route name
"{controller}/{action}/", // URL with parameters
new { controller = "Login", action = "Index" } // Parameter defaults
);
routes.MapRoute(
"DefaultWithValue", // Route name
"{controller}/{action}/{id}", // URL with parameters
new { controller = "Login", action = "Index", id = UrlParameter.Optional } // Parameter defaults
);

Answer 2

Well from the exception that action can't be determines is pretty clear that actions are resolved first then data binder comes into play and examines action's parameters and tries to data bind values to them. Makes perfect sense.
This makes perfect sense. There would be no point in first trying to data bind values to all possible types and see what we get and then look for an appropriate action. That would be next to impossible.
So. Since action selection is the problem here I guess the best (and only) way to solve this (if I don't want to use a multifaceted single action method) is to write a custom action method selector attribute.
You can read all the details and get the code on my blog:
Improving Asp.net MVC maintainability and RESTful conformance