c# mvc get url parameter within an attribute

In my controller I have this "SomeAttribute" which validates an url. It checks whether the provided ID in the url is a valid ID and whether the category name is the relevant category name of the given ID.

[SomeAttribute]
public ActionResult SomeAction() 
{
    ....
}

However, in my attribute I don't know how can I reach the current url parameters.

public SomeAttribute : ActionFilterAttribute {

   public override void OnActionExecuting(ActionExecutingContext filterContext) {
      string myurl = HttpContext.Current.Request["mystring"] // this does not work
   }
}

So basically my question is, how can I reach the url of the curr开发者_运维问答ent context within an attribute?

Well in case you need url parameters within an attribute and you are using routing, this is the solution:

filterContext.RouteData.Values["mystring"]