URL Routing on ASP.net, need to get a parameter from the url

The quick answer is use:

routes.MapPageRoute(
   "groupname",
   "{group}",
   "~/public/viewgroup"
);

And then instead of (or as well as) using querystring to extract the value in ~/public/viewgroup code, you would instead extract the groupname from RouteData as follows.

ControllerContext.RouteData.Values["groupname"];

The other option is use the IIS rewrite module.

<rewrite>
    <rules>
        <rule name="groupname">
            <match url="^([^/]*)$" />
            <action type="Rewrite" url="public/viewgroup?group={R:1}" />
        </rule>
    </rules>
</rewrite>

If you really must pass the value as a new querystring value, and want to use Routing, then things get tricky. You actually have to define a custom handler and rewrite the path in order to append the routing values to the querystring.

public class RouteWithQueryHandler : PageRouteHandler
{
    public RouteWithQueryHandler(string virtualPath, bool checkPhysicalUrlAccess)
        : base(virtualPath, checkPhysicalUrlAccess)
    {
    }

    public RouteWithQueryHandler(string virtualPath)
        :base(virtualPath)
    {
    }

    public override IHttpHandler GetHttpHandler(RequestContext requestContext)
    {
        var request = requestContext.HttpContext.Request;
        var query  = HttpUtility.ParseQueryString(request.Url.Query);
        foreach (var keyPair in requestContext.RouteData.Values)
        {
            query[HttpUtility.UrlEncode(keyPair.Key)] = HttpUtility.UrlEncode(
                                               Convert.ToString(keyPair.Value));
        }
        var qs = string.Join("&", query);
        requestContext.HttpContext.RewritePath(
                             requestContext.HttpContext.Request.Path, null, qs);
        return base.GetHttpHandler(requestContext);
    }
}

This can be registered as follows:

routes.Add("groupname", new Route("{groupname}/products.aspx",     
           new RouteWithQueryHandler("~/products.aspx", true)));

It's quite a lot of work to avoid just pulling the value out to the Routing data.

ASP.NET MVC path style arguments (parameters) can be accessed in C# controller like so. Path argument to be retrieved is "id" which returns a value of "123".

MVC Routing

public static void RegisterRoutes(RouteCollection routes)
{
    routes.MapRoute(
        "Default",
        "{controller}/{action}/{id}",
        new { id = RouteParameter.Optional });
}

//Test URL: http://localhost/MyProject/Test/GetMyId/123

MyController.cs

public class TestController : Controller
{
    public string GetMyId()
    {
        //ANSWER -> ControllerContext.RouteData.Values["id"]
        return ControllerContext.RouteData.Values["id"].ToString();
    }
}