Question

I need to use jQuery to do some validation on a DropDownList. Therefore I am trying to add a htmlAttribute like this:

@Html.DropDownList("category_id", "Vælg..", new { @class = "required" })

I am getting the following errors:

Error   2   'System.Web.Mvc.HtmlHelper<MvcApplication3.Models.Question>' does not contain a definition for 'DropDownList' and the best extension method overload 'System.Web.Mvc.Html.SelectExtensions.DropDownList(System.Web.Mvc.HtmlHelper, string, System.Collections.Generic.IEnumerable<System.Web.Mvc.SelectListItem>, string)' has some invalid arguments   c:\Users\Kenan\Documents\Visual Studio 2010\Projects\MvcApplication3 - Copy\MvcApplication3\Views\AdminQuestion\GridQuestion.cshtml 38  14  MvcApplication3
Error   3   Argument 3: cannot convert from 'string' to 'System.Collections.Generic.IEnumerable<System.Web.Mvc.SelectListItem>' c:\Users\Kenan\Documents\Visual Studio 2010\Projects\MvcApplication3 - Copy\MvcApplication3\Views\AdminQuestion\GridQuestion.cshtml 38  47  MvcApplication3
Error   4   Argument 4: cannot convert from 'AnonymousType#1' to 'string'   c:\Users\Kenan\Documents\Visual Studio 2010\Projects\MvcApplication3 - Copy\MvcApplication3\Views\AdminQuestion\GridQuestion.cshtml 38  57  MvcApplication3

If I change the code to:

@Html.DropDownList("category_id", null, new { @class = "required " })

It works, but without a default value, which is not what I want.

What am I doing wrong?

Answer 1

You’ll notice in the Overload List that there’s no overload for string, string, object.

The overload you may be looking for is:

DropDownList(HtmlHelper, String, IEnumerable<SelectListItem>, Object)

You’d write this in your view as:

@Html.DropDownList("SomeString", MyEnumerable, new {@class = "required"}

The reason your second example works, i.e. string, null, object is because IEnumerable<T> is nullable.

UPDATE

You may find that DropDownListFor is a better match for what you need.

The exact overload you’ll probably want is:

HtmlHelper<TModel>, Expression<Func<TModel, TProperty>>, IEnumerable<SelectListItem>, Object

implimented as:

@Html.DropDownListFor(m => m.category_id, ViewBag.category_id, new {@class = "required"})