System.Web.mvc.HtmlHelper does not contain a definition for EnumDropDownListFor

Question

I have been following this tutorial http://blogs.msdn.com/b/stuartleeks/archive/2010/05/21/asp-net-mvc-creating-a-dropdownlist-helper-for-enums.aspx but I run into the error "System.Web.Mvc.HtmlHelper does not contain a definition for EnumDropDownListFor".

Model:

public enum Codes
{
    IBC2012,
    IBC2009,
    IBC2006,
    FL2010,
    CBC2007
}

public class Code
{
    public int ID { get; set; }
    public int Active { get; set; }
    public string Description { get; set; }
    public string Edition { get; set; }
    public Codes Code { get; set; }
}

Controller:

public static MvcHtmlString EnumDropDownListFor<TModel, TEnum>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TEnum>> expression)
    {
        ModelMetadata metadata = ModelMetadata.FromLambdaExpression(expression, htmlHelper.ViewData);
        IEnumerable<TEnum> values = Enum.GetValues(typeof(TEnum)).Cast<TEnum>();

        IEnumerable<SelectListItem> items =
            values.Select(value => new SelectListItem
            {
                Text = value.ToString(),
                Value = value.ToString(),
                Selected = value.Equals(metadata.Model)
            });

        return htmlHelper.DropDownListFor(
            expression,
            items
            );
    }

HTML Helper:

@Html.EnumDropDownListFor(model => model.Code.Codes)

Answer 1

You forgot to bring the extension method in scope inside the view. This EnumDropDownListFor method is defined in some static class inside a namespace, right?

namespace AppName.SomeNamespace
{
    public static class HtmlExtensions
    {
        public static MvcHtmlString EnumDropDownListFor<TModel, TEnum>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TEnum>> expression)
        {
            ...
        }
    }
}

You need to add this namespace inside the view in which you want to use this helper:

@using AppName.SomeNamespace
@model MyViewModel
...
@Html.EnumDropDownListFor(model => model.Code.Codes)

And to avoid adding this using clause to all your Razor views you could also add it to the <namespaces> section of your ~/Views/web.config file:

<system.web.webPages.razor>
    <host factoryType="System.Web.Mvc.MvcWebRazorHostFactory, System.Web.Mvc, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
    <pages pageBaseType="System.Web.Mvc.WebViewPage">
      <namespaces>
        <add namespace="System.Web.Mvc" />
        <add namespace="System.Web.Mvc.Ajax" />
        <add namespace="System.Web.Mvc.Html" />
        <add namespace="System.Web.Routing" />
        <add namespace="AppName.SomeNamespace" />
      </namespaces>
    </pages>
</system.web.webPages.razor>

Answer 2

Change your namespace to

namespace System.Web.Mvc
{
    public static class HtmlExtensions
    {
...