Optgroup drop-down support in MVC - Problems with Model Binding

Question

I wonder if anyone can shed some light on this problem..

I\'ve got an option group drop-down for selecting a person\'s ethnicity – however it’s not storing the value in

Answer 1

Your select doesn't have a name attribute and so when you submit the form the selected value is not sent to the server. You need to add a name:

select.GenerateId(name);
select.MergeAttribute("name", name);

Answer 2

This is supported natively using SelectListGroup as of ASP.NET MVC 5.2:

var items = new List<SelectListItem>(); 
var group1 = new SelectListGroup() { Name = "Group 1" };
items.Add(new SelectListItem() { Text = "Item1", Group = group1 }); 

Then in MVC, do

@Html.DropDownList("select", items) 

Answer 3

Just changed the helper class to get it work for MVC 3 and with nullable int. Thanks a lot for the class, saves me plenty of time.

public static class GroupDropListExtensions
{
    public static MvcHtmlString GroupDropList(this HtmlHelper helper, string name, IEnumerable<GroupDropListItem> data, int? SelectedValue, object htmlAttributes)
    {
        if (data == null && helper.ViewData != null)
            data = helper.ViewData.Eval(name) as IEnumerable<GroupDropListItem>;
        if (data == null) return new MvcHtmlString(string.Empty);

        var select = new TagBuilder("select");

        if (htmlAttributes != null)
            select.MergeAttributes(new RouteValueDictionary(htmlAttributes));

        select.GenerateId(name);
        select.MergeAttribute("name", name);

        var optgroupHtml = new StringBuilder();
        var groups = data.ToList();
        foreach (var group in data)
        {
            var groupTag = new TagBuilder("optgroup");
            groupTag.Attributes.Add("label", helper.Encode(group.Name));
            var optHtml = new StringBuilder();
            foreach (var item in group.Items)
            {
                var option = new TagBuilder("option");
                option.Attributes.Add("value", helper.Encode(item.Value));
                if (SelectedValue != 0 && item.Value == SelectedValue)
                    option.Attributes.Add("selected", "selected");
                option.InnerHtml = helper.Encode(item.Text);
                optHtml.AppendLine(option.ToString(TagRenderMode.Normal));
            }
            groupTag.InnerHtml = optHtml.ToString();
            optgroupHtml.AppendLine(groupTag.ToString(TagRenderMode.Normal));
        }
        select.InnerHtml = optgroupHtml.ToString();
        return new MvcHtmlString(select.ToString(TagRenderMode.Normal));
    }
}

public class GroupDropListItem
{
    public string Name { get; set; }
    public List<OptionItem> Items { get; set; }
}

public class OptionItem
{
    public string Text { get; set; }
    public int Value { get; set; }
}