Monthly filter webpart

Scenario:
Monthly filter webpart to filter any list which contains datetime column.


Solution:
This solution depends upon one of the column of the list you want to filter. You need to create a new column name 'Month' with the following calculated formula.

=MONTH(Created)&"/"&"1"&"/"&YEAR(Created)

Code:

using System;
using System.Collections.Specialized;
using System.Runtime.InteropServices;
using System.Web.UI;

namespace MonthlyFilter
{
    public class MonthlyFilter : System.Web.UI.WebControls.WebParts.WebPart
    {            
        protected override void Render(HtmlTextWriter output)
        {
            base.Render(output);
            string fieldName = "Month";

            NameValueCollection variables = new NameValueCollection(this.Page.Request.QueryString);

            string queryParameter1 = "FilterField1";
            if (!string.IsNullOrEmpty(variables[queryParameter1]))
                variables.Remove(queryParameter1);

            string queryParameter2 = "FilterValue1";
            if (!string.IsNullOrEmpty(variables[queryParameter2]))
                variables.Remove(queryParameter2);

            variables.Add(queryParameter1, fieldName);
            variables.Add(queryParameter2, "{0}");

            string queryString = string.Empty;

            foreach (String s in variables)
            {
                queryString += s + "=" + variables[s] + "&";
            }

            output.WriteLine(@"<div style='background-color:yellow;float:right'>");
            
            int year = DateTime.Today.Year; 
            for( int month=1 ; month <=12 ; month ++ ) 
            {
                DateTime tempdate = new DateTime(year, month, 1);
                output.WriteLine(string.Format("<a href='{0}?{1}'>{2}</a> | ", this.Page.Request.Path, string.Format(queryString, tempdate.ToString("M/d/yyyy")), tempdate.ToString("MMM")));
            }
            output.WriteLine(@"</div>");
        }
    }
}

Scope for improvements:
A lot infact, but to start with making the field name, format, styling more generic can be helpful. I am tired ..will do it later.