MVC 3 checkbox list for

CheckBoxListFor.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using System.Linq.Expressions;

public static class CheckBoxListForExtensions
{
    public static MvcHtmlString CheckBoxListFor<TModel, TValue>(this HtmlHelper<TModel> html, Expression<Func<TModel, TValue>> expression, SelectList selectList)
    {
        ModelMetadata metadata = ModelMetadata.FromLambdaExpression(expression, html.ViewData);

        string htmlFieldName = ExpressionHelper.GetExpressionText(expression);
        string listHTML = "<ul>";
        int[] selectedValues = (int[])selectList.SelectedValue;
        foreach (var selectListItem in selectList)
        {
            if (selectedValues != null && selectedValues.Contains(int.Parse(selectListItem.Value)))
            {
                selectListItem.Selected = true;
            }
            var id = selectListItem.Value + selectListItem.Text;
            listHTML += "<li>";
            listHTML += String.Format("<input type='checkbox' name='{0}' value='{1}' {2} id='{3}' />"
                , new object[] { htmlFieldName, selectListItem.Value, (selectListItem.Selected == true ? "checked='checked'" : ""), id });
            listHTML += String.Format("<label for='{0}'>{1}</label>", id, selectListItem.Text);
            listHTML += "</li>";
        }
        listHTML += "</ul>";

        return MvcHtmlString.Create(listHTML);
    }
}