UserControl rendering: write link to current page?

Question

I'm implementing a custom control and in this control I need to write a bunch of links to the current page, each one with a different query parameter. I need to keep existing query string intact, and add (or modify the value of ) an extra query item (eg. "page"):

"Default.aspx?page=1"
"Default.aspx?page=2"
"Default.aspx?someother=true&page=2"

etc.

Is there a simple helper method that I can use in the Render method ... uhmm ... like:

Page.ClientScript.SomeURLBuilderMethodHere(this,"page","1");
Page.ClientScript.SomeURLBuilderMethodHere(this,"page","2");

That will take care of generating a correct URL, maintain existing query string items and not create duplicates eg. page=1&page=2&page=3?

Rolling up my own seems like such an unappealing task.

Answer 1

I'm afraid I don't know of any built-in method for this, we use this method that takes the querystring and sets parameters

    /// <summary>
    /// Set a parameter value in a query string. If the parameter is not found in the passed in query string,
    /// it is added to the end of the query string
    /// </summary>
    /// <param name="queryString">The query string that is to be manipulated</param>
    /// <param name="paramName">The name of the parameter</param>
    /// <param name="paramValue">The value that the parameter is to be set to</param>
    /// <returns>The query string with the parameter set to the new value.</returns>
    public static string SetParameter(string queryString, string paramName, object paramValue)
    {
        //create the regex
        //match paramname=*
        //string regex = String.Format(@"{0}=[^&]*", paramName);
        string regex = @"([&?]{0,1})" + String.Format(@"({0}=[^&]*)", paramName);

        RegexOptions options = RegexOptions.RightToLeft;
  // Querystring has parameters...
        if (Regex.IsMatch(queryString, regex, options))
        {
            queryString = Regex.Replace(queryString, regex, String.Format("$1{0}={1}", paramName, paramValue));
        }
        else
        {
   // If no querystring just return the Parameter Key/Value
   if (queryString == String.Empty)
   {
    return String.Format("{0}={1}", paramName, paramValue);
   }
   else
   {
    // Append the new parameter key/value to the end of querystring
    queryString = String.Format("{0}&{1}={2}", queryString, paramName, paramValue);
   }
        }
        return queryString;
    }

Obviously you could use the QueryString NameValueCollection property of the URI object to make looking up the values easier, but we wanted to be able to parse any querystring.

Answer 2

Oh and we have this method too that allows you to put in a whole URL string without having to get the querystring out of it

public static string SetParameterInUrl(string url, string paramName, object paramValue)
{
    int queryStringIndex = url.IndexOf("?");
    string path;
    string queryString;
    if (queryStringIndex >= 0 && !url.EndsWith("?"))
    {
        path = url.Substring(0, queryStringIndex);
        queryString = url.Substring(queryStringIndex + 1);
    }
    else
    {
        path = url;
        queryString = string.Empty;
    }
    return path + "?" + SetParameter(queryString, paramName, paramValue);
}