DropDownList HtmlHelper Extension

DropDownListFor_SelectListProviderAttribute.cs

public static MvcHtmlString DropDownListFor<TModel, TProperty>(this HtmlHelper<TModel> html, Expression<Func<TModel, TProperty>> expression) where TModel : class
{
    var property = expression.GetProperty();
    IEnumerable<SelectListItem> selectList;

    var selectListProviderAttribute = property.GetAttribute<SelectListProviderAttribute>();

    if (selectListProviderAttribute != null)
    {
        var provider = selectListProviderAttribute.Provider;
        selectList = provider.Provide();
    }
    else
    {
        throw new ArgumentException(string.Format("SelectListProvider not specified for property \"{0}\"", property.Name));
    }

    return html.DropDownListFor(expression, selectList);
}