Can't add htmlAttribute to Html.DropDownList

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?

Jamie Dixon · Accepted Answer · 2011-07-03 23:54:28Z

2

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"})

edited Jul 3, 2011 at 23:54

answered Jul 3, 2011 at 23:24

Jamie Dixon

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12 Comments

Nanek Over a year ago

What should i write in the HtmlHelper parameter?

Jamie Dixon Over a year ago

That's already covered by the @Html bit you're using. It's the same as other extension methods where the first parameter is specificed as (this HtmlHelper,...). So you can ignore that parameter knowing it's covered by your @Html part.

Nanek Over a year ago

I am getting the SelectList from the ViewBag. It is called ViewBag.category_id - I have changed the code to this: @Html.DropDownList("Kategorier", ViewBag.category_id, new { @class = "required" } ) but i am getting this error:

Nanek Over a year ago

Error 1 'System.Web.Mvc.HtmlHelper<MvcApplication3.Models.Question>' has no applicable method named 'DropDownList' but appears to have an extension method by that name. Extension methods cannot be dynamically dispatched. Consider casting the dynamic arguments or calling the extension method without the extension method syntax. c:\Users\Kenan\Documents\Visual Studio 2010\Projects\MvcApplication3 - Copy\MvcApplication3\Views\AdminQuestion\GridQuestion.cshtml 38 10 MvcApplication3

Jamie Dixon Over a year ago

What is category_id ??? If it's an int, there's no overload for string, int, object. Does this make sense?

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