Change Single URL query string value

You can’t modify the QueryString directly as it is readonly. You will need to get the values, modify them, then put them back together. Try this:

var nameValues = HttpUtility.ParseQueryString(Request.QueryString.ToString());
nameValues.Set("page", "2");
string url = Request.Url.AbsolutePath;
string updatedQueryString = "?" + nameValues.ToString();
Response.Redirect(url + updatedQueryString);

The ParseQueryString method returns a NameValueCollection (actually it really returns a HttpValueCollection which encodes the results, as I mention in an answer to another question). You can then use the Set method to update a value. You can also use the Add method to add a new one, or Remove to remove a value. Finally, calling ToString() on the name NameValueCollection returns the name value pairs in a name1=value1&name2=value2 querystring ready format. Once you have that append it to the URL and redirect.

Alternately, you can add a new key, or modify an existing one, using the indexer:

nameValues["temp"] = "hello!"; // add "temp" if it didn't exist
nameValues["temp"] = "hello, world!"; // overwrite "temp"
nameValues.Remove("temp"); // can't remove via indexer

You may need to add a using System.Collections.Specialized; to make use of the NameValueCollection class.

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