Question

I need a class to manipulate URLs in asp.net WebForms

eg

Url url = new Url("http://www.stackoverflow.com");

if(!url.Params.Contains("user"))
  url.Params.Add("user", "1");

I have tried NameValueCollections but they seem to be readonly as do a number of objects in HttpContext

NameValueCollection nv = Request.QueryString;

nv.Remove("ForeignLanguage");
nv.Add("ForeignLanguage", l.ID.ToString());

The above generates a Collection is readonly exception

Answer 1

I would use the UriBuilder class, in conjunction with the very handy HttpUtility.ParseQueryString method:

var uri = new UriBuilder("http://www.stackoverflow.com");
NameValueCollection parameters = HttpUtility.ParseQueryString(string.Empty);
parameters.Add("user", "1");
uri.Query = parameters.ToString();
return uri.ToString();

Note the trick with passing an empty string to the ParseQueryString method – this will give you a (writable) instance of System.Web.HttpValueCollection, a non-public class that derives from NameValueCollection and (among other things) emits its contents in querystring format when you call its ToString method.

You could also manipulate the current url:

var uri = new UriBuilder(Request.Url);
NameValueCollection parameters = HttpUtility.ParseQueryString(uri.Query);
// TODO Manipulate parameters...
uri.Query = parameters.ToString();
return uri.ToString();