UriPathExtensionMapping in MVC 4 - asp.net-mvc-routing

Question

How do I use UriPathExtensionMapping in MVC4? I've added the mapping in the formatter such that:
MediaTypeMappings.Add(new UriPathExtensionMapping("json", new MediaTypeHeaderValue("application/json"))
But I can't use the extension on my route unless I add a verb, such as:
routes.MapHttpRoute(
name: "DefaultApi",
routeTemplate: "api/{controller}.{extension}"
);
Then it'll recognize my desired media type, but it also starts expecting "extension" as a parameter on the action. Example:
public object Get(string extension)
{
}
Instead of just:
public object Get()
{
}
How can I resolve this?
Thanks!

Answer 1

I don't remember if I noticed this problem, but it might be because I explicitly specified the default value for the extension like:
var rF = routes.MapHttpRoute(
name: "DefaultApi.v1.format",
routeTemplate: "api/1/{controller}/{action}.{format}/{*id}",
defaults: new { id = RouteParameter.Optional, format = "json", version = 1 }
);
*note format = "json" in the line beginning with defaults.
I did also notice that this sometimes doesn't work on requests with trailing parameters for id, like ~/api/1/values/get.json/4.

Answer 2

I can't repro this problem.
You are right that, to use UriPathExtensionMapping, you will need to specify the {controller}.{ext} in your route, like what you described above. If you only specify the {controller}, and uri looks like ~/home.json, then the controller token will be mapped to home.json, which is probably not what you wanted.
However, you should not need to require an "extension" parameter in your action. If you continue seeing this problem, can you post your entire repro, including your controller, your routes and configuration set up with custom formatter? thank you.