SelectListItem with data-attributes

Is there anyway to have a SelectList prepopulated on ViewModel with data-attributes ?

I want to do

@Html.DropdownListFor(m=> m.CityId, Model.Cities);

so it generates code like :

<select id="City" class="location_city_input" name="City">
    <option data-geo-lat="-32.522779" data-geo-lng="-55.765835" data-geo-zoom="6" />
    <option data-geo-lat="-34.883611" data-geo-lng="-56.181944" data-geo-zoom="13" data-geo-name="Montevideo" data-child=".state1" value="1">Montevideo</option>               
    <option data-geo-lat="-34.816667" data-geo-lng="-55.95" data-geo-zoom="13" data-geo-name="Canelones, Ciudad de la Costa" data-child=".state41" value="41">Ciudad de la Costa</option>
</select>

Here's the simple solution.

Not everything has to be written with extension method in .NET code. One of the great things about MVC is it gives you easy access to construct your own HTML.

With MVC4 you can get the id and name of the element on the expression tree with the helpers HTML.NameFor and HTML.IdFor

<select name="@Html.NameFor(Function(model) model.CityId)"
        id="@Html.IdFor(Function(model) model.CityId)"
        class="location_city_input">
    @For Each city In Model.Cities
        @<option value="@city.Value"
                 @(If(city.Value = Model.CityId, "selected", ""))
                 data-geo-lat="@city.Lat"
                 data-geo-lng="@city.Lng"
                 data-geo-zoom="@city.Zoom">
            @city.Text
        </option>
    Next
</select>

Assuming Model.Cities is a collection of items that expose each of those properties. Then you should be all set.

If you want reusability, consider making it an editor template for anything that is an Enumerable of Cities

You'll have to extend SelectListItem, and then extend DropDownListFor to use the extended SelectListItem.

Have a look at this solution:

Adding html class tag under <option> in Html.DropDownList

Here's how I ended up doing it without an extension but still enabling unobtrusive validation to continue to work & be bound to a ViewModel property.

Created an Html Helper to get the validation attributes as a string:

    public static IHtmlString GetUnobtrusiveValidationAttributesFor<TModel, TProperty>(this HtmlHelper<TModel> html, Expression<Func<TModel, TProperty>> propertySelector)
    {
        string propertyName = html.NameFor(propertySelector).ToString();
        ModelMetadata metaData = ModelMetadata.FromLambdaExpression(propertySelector, html.ViewData);
        IDictionary<string, object> attributeCollection = html.GetUnobtrusiveValidationAttributes(propertyName, metaData);

        return html.Raw(String.Join(" ", attributeCollection.Select(kvp => kvp.Key + "=\"" + kvp.Value.ToString() + "\"")));
    }

Use this helper in a select list in the view:

<select name="@Html.NameFor(m => m.CityId)" id="@Html.IdFor(m => m.CityId)"
    @Html.GetUnobtrusiveValidationAttributesFor(m => m.CityId)
    class="location_city_input">
    @foreach(var city in Model.Cities)
    {
        <option value="@city.Id.ToString()" @(city.Id == Model.CityId ? "selected" : "") 
            data-geo-lat="@city.Lat" data-geo-lng="@city.Lng" data-geo-zoom="@city.Zoom">
            @city.Name
        </option>
    }
</select>

This would output something like this:

<select id="CityId" name="CityId" 
    data-val-required="The SelectedTaxRateID field is required." data-val="true" 
    class="location_city_input">
    <option value="1" selected data-geo-lat="-34.883611" data-geo-lng="-56.181944" data-geo-zoom="13">Montevideo</option>               
    <option value="41" data-geo-lat="-34.816667" data-geo-lng="-55.95" data-geo-zoom="13">Ciudad de la Costa</option>
</select>

I will leave the conditional data- attributes up to you since those are just a matter of forming the appropriate Razor expressions.

MVC when it converts object names to attribute names, it relaces "_" with "-", so its:

@Html.DropDownList(a=>a.websiteid, Model.GetItems, new{ data_rel="selected" })

NOT MY ANSWER, ANSWER CREDIT GOES TO About bruce (sqlwork.com) from the ASP>NET Forums.

How can I add data-rel="selected" attribute into dropdownlistfor htmlAttributes?

JUST WANTED TO HELP OUT AS THIS SAVED ME FROM CODING A HACK! ENJOY.

I had a similar requirement, I created a extension. Hope it helps for the ones who wants to create an extension.

/*cs file*/
/*This contains your information with List<vmListItem>*/
public class vmListItem
{
   public int Id { get; set; }
   public string Name { get; set; }
   public string Tag { get; set; }
}

/*This contains the attributes in select, using List<vmAttribute>. Check cshtml */
public class vmAttribute
{
   public string Key { get; set; }
   public string Value { get; set; }
}

    /// <summary>
    /// Creates a dropdownlist using a list with data attributes included
    /// </summary>
    /// <param name="helper"></param>
    /// <param name="id">id and name of the select</param>
    /// <param name="attributes">list of attrs for select</param>
    /// <param name="items"><list of options/param>
    /// <param name="idSelected">id selected in option</param>
    /// <param name="tagName">data-tagName you can choose the name of your tag</param>
    /// <param name="textHeader">first option in select</param>
    /// <returns></returns>
    public static MvcHtmlString DropDownListForWithTag(this HtmlHelper helper, string id, List<vmAttribute> attributes, List<vmListItem> items, int idSelected, string tagName = "tag", string textHeader= "")
    {
        var select = new TagBuilder("select");
        select.GenerateId(id);
        select.MergeAttribute("name", id);
        foreach (vmAttribute att in atributos) select.MergeAttribute(att.Key, att.Value);

        TagBuilder headerOption = new TagBuilder("option");
        headerOption .MergeAttribute("value", null);
        headerOption .InnerHtml = textHeader;
        select.InnerHtml += headerOption ;

        foreach(var item in items)
        {                
            TagBuilder option = new TagBuilder("option");
            option.MergeAttribute("value", item.Id.ToString());
            option.MergeAttribute("data-" + tagName, item.Tag);
            if (idSelected == item.Id) option.MergeAttribute("selected", "selected");
            option.InnerHtml = item.Name;

            select.InnerHtml += option.ToString();
        }

        return new MvcHtmlString(select.ToString());
    }

/*cshtml file*/
@Html.DropDownListForWithTag("MovimientoBienMotivoId", new List<vmAttribute> {
                        new vmAttribute("class", "form-control"),
                        new vmAttribute("data-val", "true"),
                        new vmAttribute("data-val-required", "El campo Motivo es obligatorio"),
                        new vmAttribute("onchange", "movValidarCambioMotivo()"),
                    }, (List<vmListItem>)ViewBag.MovimientoBienMotivoId, Model.MovimientoBienMotivoId, "codigo", "Seleccione")
                    @Html.ValidationMessageFor(model => model.ColumnId, "", new { @class = "text-danger" })


/*html results*/