Optional routing parameter with constraint in ASP.NET MVC 2?

问题

If I have a route like this:

routes.Add(new Route("{controller}/{page}", 
    new RouteValueDictionary
    {
        { "page", UrlParameter.Optional }
    },
    new RouteValueDictionary
    {
        { "page", @"[Pp]age\d+" }
    }, 
    new MvcRouteHandler()
));

Then the route doesn't match when {page} is missing, however if I remove the constraint it matches. Is this a bug or a feature?

回答1:

It's a feature: how can the constraint match if the parameter if optional? You might either want to set the default value for "page" to "Page1" to resolve your problem, or replace your regex with "([Pp]age\d+)?" to allow nothing to match (I'm not sure about this one and can't test it atm).

回答2:

I'm using ^$| within a regex, such as: (^$|[Pp]age\d+). I found this question while searching for an answer to this and figured I'd add what I found here.

routes.MapRoute(
  name: "News Archive",
  url: "News/{page}",
  defaults: new { controller = "news", action = "List", page= UrlParameter.Optional },
  constraints: new { page= @"^$|[0-9][0-9]" });

来源：https://stackoverflow.com/questions/3468115/optional-routing-parameter-with-constraint-in-asp-net-mvc-2