Question

I’d like to generate a new URL based on the existing route, but will add a new parameter ‘page’
Here are a few examples:

old: ~/localhost/something?what=2
new: ~/localhost/something?what=2&page=5

old: ~/localhost/Shoes
new: ~/localhost/Shoes/5

I can not just append &page=5 to existing url because routes may be different.
Some use the query string and some do not.

Answer 1

I had a similar issue, and took the approach of extending the UrlHelper. The code in the View looks like:

<a href="<%= Url.AddPage(2) %>">Page 2</a>

The UrlHelper extension looks like:

using System.Web.Mvc;
using System.Web.Routing;
using System.Collections.Specialized;

public static class UrlHelperExtension
{
    public static string AddPage(this UrlHelper helper, int page)
    {

        var routeValueDict = new RouteValueDictionary
        {
            { "controller", helper.RequestContext.RouteData.Values["controller"] },
            { "action" , helper.RequestContext.RouteData.Values["action"]}
        };

        if (helper.RequestContext.RouteData.Values["id"] != null)
        {
            routeValueDict.Add("id", helper.RequestContext.RouteData.Values["id"]);
        }

        foreach (string name in helper.RequestContext.HttpContext.Request.QueryString)
        {
            routeValueDict.Add(name, helper.RequestContext.HttpContext.Request.QueryString[name]);
        }

        routeValueDict.Add("page", page);

        return helper.RouteUrl(routeValueDict);
    }
}

A couple of notes: I check for the ID, since I don’t use it in all my routes. I add the Page route value at the end, so it is the last url parameter (otherwise you could add it in the initial constructor).