How to add a htmlAttributes in this HtmlHelper?

Question

I'm using right now this code to implement a RadioButtonList using MVC4.

And as you can see, that function does not have htmlAttributes parameter. So I'd like to add it and here is the problem. Check please that the htmlAttributes for RadioButtonFor() is occupied by the id.

I was trying to add it but throws me errors because the id already exists for the loop.

public static class HtmlExtensions
{
    public static MvcHtmlString RadioButtonForSelectList<TModel, TProperty>(
        this HtmlHelper<TModel> htmlHelper,
        Expression<Func<TModel, TProperty>> expression,
        IEnumerable<SelectListItem> listOfValues)
    {
        return htmlHelper.RadioButtonForSelectList(expression, listOfValues, null);
    }

    public static MvcHtmlString RadioButtonForSelectList<TModel, TProperty>(
        this HtmlHelper<TModel> htmlHelper,
        Expression<Func<TModel, TProperty>> expression,
        IEnumerable<SelectListItem> listOfValues,
        object htmlAttributes)
    {
        return htmlHelper.RadioButtonForSelectList(expression, listOfValues, new RouteValueDictionary(htmlAttributes));
    }

    public static MvcHtmlString RadioButtonForSelectList<TModel, TProperty>(
        this HtmlHelper<TModel> htmlHelper,
        Expression<Func<TModel, TProperty>> expression,
        IEnumerable<SelectListItem> listOfValues,
        IDictionary<string, object> htmlAttributes)
    {
        var metaData = ModelMetadata.FromLambdaExpression(expression, htmlHelper.ViewData);
        var sb = new StringBuilder();
        if (listOfValues != null)
        {
            foreach (SelectListItem item in listOfValues)
            {
                var id = string.Format(
                    "{0}_{1}",
                    metaData.PropertyName,
                    item.Value
                );

                var radio = htmlHelper.RadioButtonFor(expression, item.Value, new { id = id }).ToHtmlString();
                sb.AppendFormat(
                    "{0}<label for=\"{1}\">{2}</label>",
                    radio,
                    id,
                    HttpUtility.HtmlEncode(item.Text)
                );
            }
        }
        return MvcHtmlString.Create(sb.ToString());
    }
}

Answer 1

In the third method, it looks like the html attributes being passed to the radion button being created is new { id = id }. Try to replace that with the parameter from the method.

UPDATED

Include id in the html attributes and assign a new value to id in each loop iteration.

if (listOfValues != null)
{
    if (!htmlAttributes.ContainsKey("id"))
    {
        htmlAttributes.Add("id", null);
    }
    foreach (SelectListItem item in listOfValues)
    {
        var id = string.Format(
            "{0}_{1}",
            metaData.PropertyName,
            item.Value
        );
        htmlAttributes["id"] = id;
        var radio = htmlHelper.RadioButtonFor(expression, item.Value, htmlAttributes).ToHtmlString();
        sb.AppendFormat(
            "{0}<label for=\"{1}\">{2}</label>",
            radio,
            id,
            HttpUtility.HtmlEncode(item.Text)
        );
    }
}