extracting parameter from a url using C#

extracting parameter from a url using C#

where i am looking for key in the url.Query

Regex fileRegex = new Regex(@"^\?key=(?<1>[^&]*)$", RegexOptions.Singleline | RegexOptions.IgnoreCase);
Match fileMatch = fileRegex.Match(Uri.UnescapeDataString(url.Query));
if (fileMatch.Success)
return fileMatch.Groups[1].Value;