ASP.NET MVC Enumeration Dropdown Extensions

EnumDropdownExtenstions.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using System.Text.RegularExpressions;
using System.Web.Mvc;
using System.Web.Mvc.Html;

namespace System.Web.Mvc.Html
{
    public static class EnumDropdownExtenstions
    {
        /// <summary>
        /// Returns an HTML select element for the property specified by the
        /// expression, presenting the values with custom readable names.
        /// </summary>
        /// <typeparam name="TModel">The type of the model.</typeparam>
        /// <typeparam name="TProperty">The type of the value.</typeparam>
        /// <param name="htmlHelper">The HTML helper instance that this method extends.</param>
        /// <param name="expression">
        /// An expression that identifies the object that contains the properties to
        /// display.
        /// </param>
        /// <returns>
        /// An HTML select element for the property specified by the
        /// expression, presenting the values with custom readable names.
        /// </returns>
        /// <exception cref="System.ArgumentException">
        /// The expression is not an enumeration type.
        /// </exception>
        public static MvcHtmlString EnumDropDownListFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression)
        {
            return htmlHelper.EnumDropDownListFor(expression, value =>
                {
                    return Regex.Replace(
                        Regex.Replace(
                            value.ToString(),
                            @"[a-z][A-Z]+",
                            m => string.Concat(m.Value[0], ' ', m.Value.Substring(1))),
                        @"[A-Z]{2,}[a-z]",
                        m => string.Concat(m.Value.Substring(0, m.Length - 2), ' ', m.Value.Substring(m.Length - 2)));
                });
        }

        /// <summary>
        /// Returns an HTML select element for the property specified by the
        /// expression, presenting the values with custom readable names.
        /// </summary>
        /// <typeparam name="TModel">The type of the model.</typeparam>
        /// <typeparam name="TProperty">The type of the value.</typeparam>
        /// <param name="htmlHelper">The HTML helper instance that this method extends.</param>
        /// <param name="expression">
        /// An expression that identifies the object that contains the properties to
        /// display.
        /// </param>
        /// <param name="displayValue">
        /// A function to convert an enumeration value into a readable name.
        /// </param>
        /// <returns>
        /// An HTML select element for the property specified by the
        /// expression, presenting the values with custom readable names.
        /// </returns>
        /// <exception cref="System.ArgumentException">
        /// The expression is not an enumeration type.
        /// </exception>
        public static MvcHtmlString EnumDropDownListFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression, Func<TProperty, string> displayValue)
        {
            return htmlHelper.EnumDropDownListFor(expression, displayValue, null, null);
        }

        /// <summary>
        /// Returns an HTML select element for the property specified by the
        /// expression, presenting the values with custom readable names.
        /// </summary>
        /// <typeparam name="TModel">The type of the model.</typeparam>
        /// <typeparam name="TProperty">The type of the value.</typeparam>
        /// <param name="htmlHelper">The HTML helper instance that this method extends.</param>
        /// <param name="expression">
        /// An expression that identifies the object that contains the properties to
        /// display.
        /// </param>
        /// <param name="displayValue">
        /// A function to convert an enumeration value into a readable name.
        /// </param>
        /// <returns>
        /// An HTML select element for the property specified by the
        /// expression, presenting the values with custom readable names.
        /// </returns>
        /// <exception cref="System.ArgumentException">
        /// The expression is not an enumeration type.
        /// </exception>
        public static MvcHtmlString EnumDropDownListFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression, Func<TProperty, string> displayValue, object htmlAttributes)
        {
            return htmlHelper.EnumDropDownListFor(expression, displayValue, null, htmlAttributes);
        }

        /// <summary>
        /// Returns an HTML select element for the property specified by the
        /// expression, presenting the values with custom readable names.
        /// </summary>
        /// <typeparam name="TModel">The type of the model.</typeparam>
        /// <typeparam name="TProperty">The type of the value.</typeparam>
        /// <param name="htmlHelper">The HTML helper instance that this method extends.</param>
        /// <param name="expression">
        /// An expression that identifies the object that contains the properties to
        /// display.
        /// </param>
        /// <param name="displayValue">
        /// A function to convert an enumeration value into a readable name.
        /// </param>
        /// <returns>
        /// An HTML select element for the property specified by the
        /// expression, presenting the values with custom readable names.
        /// </returns>
        /// <exception cref="System.ArgumentException">
        /// The expression is not an enumeration type.
        /// </exception>
        public static MvcHtmlString EnumDropDownListFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression, Func<TProperty, string> displayValue, string optionLabel, object htmlAttributes)
        {
            Type enumType;
            bool isOptional;
            var propertyType = typeof(TProperty);
            if (propertyType.IsEnum)
            {
                enumType = propertyType;
                isOptional = false;
            }
            else if (propertyType.IsGenericType && propertyType.GetGenericTypeDefinition() == typeof(Nullable<>) && propertyType.GetGenericArguments().Single().IsEnum)
            {
                enumType = propertyType.GetGenericArguments().Single();
                isOptional = true;
            }
            else
                throw new ArgumentException("property is not an enumeration type.", "expression");

            var selected = expression.Compile().Invoke(htmlHelper.ViewData.Model);
            var selectList = Enum.GetValues(enumType).Cast<TProperty>().OrderBy(p => p.ToString()).Select(p => new SelectListItem { Value = p.ToString(), Text = displayValue(p), Selected = p.Equals(selected) }).ToList();
            if (isOptional)
                selectList.Insert(0, new SelectListItem { Value = string.Empty, Text = string.Empty, Selected = selected.Equals(null) });

            return htmlHelper.DropDownListFor(expression, selectList, optionLabel, htmlAttributes);
        }
    }
}

I implement Globalization!

Great!
But it would be nice could if you could use the Display(Name = ...) attribute on enums. But that can be fixed when passing this as a function for displayValue:

I use: e => e.DisplayName() as parameter for the displayValue.

And created an extension method to the enum:

public static class EnumExtensions
{
    public static string DisplayName(this Enum value)
    {
        Type enumType = value.GetType();
        var enumValue = Enum.GetName(enumType, value);
        MemberInfo member = enumType.GetMember(enumValue)[0];

        var attrs = member.GetCustomAttributes(typeof(DisplayAttribute), false);
        var outString = ((DisplayAttribute)attrs[0]).Name; //TODO Null check

        if (((DisplayAttribute)attrs[0]).ResourceType != null)
        {
            outString = ((DisplayAttribute)attrs[0]).GetName();
        }

        return outString;
    }
}