gistfile1.cs

	public static class HtmlExtensions
	{
	 public static IHtmlString DropDownListFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression,
                                                                          Dictionary<string, IEnumerable<SelectListItem>> selectList)
        {
            /*
             * <select name="tmodel">
             *   <optgroup label="Items">
             *   <option value="item">Item</option>
             * </select>
             */

            var select = new TagBuilder("select");
            select.Attributes.Add("name", ExpressionHelper.GetExpressionText(expression));
            select.Attributes.Add("id", ExpressionHelper.GetExpressionText(expression));

            var propertyValue = ModelMetadata.FromLambdaExpression(expression, htmlHelper.ViewData).Model;

            var optgroups = new StringBuilder();

            foreach (var kvp in selectList)
            {
                var optgroup = new TagBuilder("optgroup");
                optgroup.Attributes.Add("label", kvp.Key);

                var options = new StringBuilder();

                foreach (var item in kvp.Value)
                {
                    var option = new TagBuilder("option");

                    option.Attributes.Add("value", item.Value);
                    option.SetInnerText(item.Text);

                    if (item.Selected || (propertyValue != null && propertyValue.ToString() == item.Value))
                    {
                        option.Attributes.Add("selected", "selected");
                    }

                    options.Append(option.ToString(TagRenderMode.Normal));
                }

                optgroup.InnerHtml = options.ToString();

                optgroups.Append(optgroup.ToString(TagRenderMode.Normal));
            }

            select.InnerHtml = optgroups.ToString();

            return MvcHtmlString.Create(select.ToString(TagRenderMode.Normal));
        }
    }
	}