How do I add a validationmessage to my custom HtmlHelper?

Question

I have a class where I have used data annotations:

[Required(ErrorMessage = "You must indicate which sex you are.)]
public string Sex { get; set; }

I have also created a custom HtmlHelper called RadioButtonListFor, which I can call like this:

@Html.RadioButtonListFor(m => m.Sex, "SexList")

My SexList is defined like this:

IList<string> SexList = new List() { "Male", "Female"};

And below is the RadioButtonListFor extension (not totally finished yet):

public static class RadioButtonListForExtentions
{
    public static IHtmlString RadioButtonListFor<TModel, TValue>(this HtmlHelper<TModel> helper, Expression<Func<TModel, TValue>> expression, string list)
    {
        string prefix = ExpressionHelper.GetExpressionText(expression);
        if (string.IsNullOrEmpty(prefix))
            prefix = "empty";
        int index = 0;

        var items = helper.ViewData.Eval(list) as IEnumerable;
        if (items == null)
            throw new NullReferenceException("Cannot find " + list + "in view data");

        string txt = string.Empty;
        foreach (var item in items)
        {
            string id = string.Format("{0}_{1}", prefix, index++).Replace('.','_');
            TagBuilder tag = new TagBuilder("input"); 
            tag.MergeAttribute("type", "radio");
            tag.MergeAttribute("name", prefix);
            tag.MergeAttribute("id", id);
            tag.MergeAttribute("data-val-required", "Missing");
            tag.MergeAttribute("data-val", "true");

            txt += tag.ToString(TagRenderMode.Normal);
            txt += item;
        }

        return helper.Raw(txt);
    }
}

My problem is this: Right now I have hardcoded the word "Missing" in the attribute "data-val-required". How do I get the text I stated in my data annotations?

Answer 1

Ah... found the solution myself, after a good nights sleep :-)

Replacing the RadioButtonListFor with the below:

public static IHtmlString RadioButtonListFor<TModel, TValue>(this HtmlHelper<TModel> helper, Expression<Func<TModel, TValue>> expression, string list)
    {
        string prefix = ExpressionHelper.GetExpressionText(expression);
        if (string.IsNullOrEmpty(prefix))
            prefix = "empty";
        int index = 0;

        var items = helper.ViewData.Eval(list) as IEnumerable;
        if (items == null)
            throw new NullReferenceException("Cannot find " + list + "in view data");

        var validationAttributes = helper.GetUnobtrusiveValidationAttributes(prefix);

        string txt = string.Empty;
        foreach (var item in items)
        {
            string id = string.Format("{0}_{1}", prefix, index++).Replace('.','_');
            TagBuilder tag = new TagBuilder("input"); 
            tag.MergeAttribute("type", "radio");
            tag.MergeAttribute("name", prefix);
            tag.MergeAttribute("id", id);
            foreach (KeyValuePair<string, object> pair in validationAttributes)
            {
                tag.MergeAttribute(pair.Key, pair.Value.ToString());
            }
            txt += tag.ToString(TagRenderMode.Normal);
            txt += item;
        }

        return helper.Raw(txt);
    }

Basically I have added "validationAttributes" which apparently is a dictionary of my validation items. And looping through these and adding them makes it work like a charm!

Edited October 13th 2011:

Ended up with the below solution. Instead of just getting a list of strings, I decided to send in a Dictionary where the key is the radiobutton value and the value of the dictionary is the radiobutton text.

public static IHtmlString RadioButtonListFor<TModel, TValue>(this HtmlHelper<TModel> helper, Expression<Func<TModel, TValue>> expression, string list)
    {
        string prefix = ExpressionHelper.GetExpressionText(expression);
        if (string.IsNullOrEmpty(prefix))
            prefix = "empty";

        // find existing value - if any
        string value = helper.ViewData.Eval(prefix) as string;

        var validationAttributes = helper.GetUnobtrusiveValidationAttributes(prefix);
        string txt = string.Empty;

        // create hidden field for error msg/value
        TagBuilder tagHidden = new TagBuilder("input");
        tagHidden.MergeAttribute("type", "hidden");
        tagHidden.MergeAttribute("name", prefix);
        tagHidden.MergeAttribute("value", value);
        tagHidden.MergeAttribute("id", prefix.Replace('.', '_'));
        foreach (KeyValuePair<string, object> pair in validationAttributes)
        {
            tagHidden.MergeAttribute(pair.Key, pair.Value.ToString());
        }
        txt += tagHidden.ToString(TagRenderMode.Normal);

        // prepare to loop through items
        int index = 0;
        var items = helper.ViewData.Eval(list) as IDictionary<string, string>;
        if (items == null)
            throw new NullReferenceException("Cannot find " + list + "in view data");

        // create a radiobutton for each item. "Items" is a dictionary where the key contains the radiobutton value and the value contains the Radiobutton text/label
        foreach (var item in items)
        {
            string id = string.Format("{0}_{1}", prefix, index++).Replace('.','_');
            TagBuilder tag = new TagBuilder("input"); 
            tag.MergeAttribute("type", "radio");
            tag.MergeAttribute("name", prefix);
            tag.MergeAttribute("id", id);
            tag.MergeAttribute("value", item.Key);
            if (item.Key == value)
                tag.MergeAttribute("checked", "true");
            tag.MergeAttribute("onclick", "javascript:" + tagHidden.Attributes["id"] + ".value='" + item.Key + "'");
            txt += tag.ToString(TagRenderMode.Normal);
            txt += item.Value;
        }

        return helper.Raw(txt);
    }