Replace item in querystring

Question

I have a URL that also might have a query string part, the query string might be empty or have multiple items.

I want to replace one of the items in the query string

Answer 1

No, the framework doesn't have any existing QueryStringBuilder class, but usually the querystring information in a HTTP request is available as an iterable and searchable NameValueCollection via the Request.Querystring property.

Since you are starting off with a Uri object, however, you will need to obtain the querystring portion using the Query property of the Uri object. This will yield a string of the form:

Uri myURI = new Uri("http://www.mywebsite.com/page.aspx?Val1=A&Val2=B&Val3=C");
string querystring = myURI.Query;

// Outputs: "?Val1=A&Val2=B&Val3=C". Note the ? prefix!
Console.WriteLine(querystring);

You can then split this string on the ampersand character to differentiate it into different querystring parameters-value pairs. Then again split each parameter on the "=" character to differentiate it into a key and value.

Since your final goal is to search for a particular querystring key and if necessary create it, you should try to (re)create a collection (preferably, a generic one) that allows you easily search in the collection, similar to the facility provided by the NameValueCollection class.