Adding Descriptions to your Enumerations

Introduction

Have you ever wanted to add a more descriptive attribute to your enums? Well, here is one way. Let's take a very simple color based enumeration called MyColors:

using System;
using System.ComponentModel;
using System.Reflection;

public enum MyColors{
   White,
   Red,
   Green
}

Now, as you know, enumerations are represented by numbers (see the docs here).

If you want to associate text, we can do so by using System.ComponentModel.DescriptionAttribute to do this.

using System;
using System.ComponentModel;
using System.Reflection;

public enum MyColors{
   [Description("The Color of my skin")]
   White,
   [Description("Bulls like this color")]
   Red,
   [Description("The color of slime")]
   Green
}

But just associating this attribute with our enum doesn't help. We need a way to access that information too. By using reflection, we can get access to all the attributes for the enumeration. The code below describes a simple accessor that will retrieve the descriptions from each enumeration.

public static string GetDescription(object enumValue, string defDesc){
        FieldInfo fi = enumValue.GetType().GetField(enumValue.ToString());
        
        if (null != fi)
        {
            object[] attrs = fi.GetCustomAttributes(typeof(DescriptionAttribute), true);
            if (attrs != null && attrs.Length > 0)
                return ((DescriptionAttribute)attrs[0]).Description;
        }

        return defDesc;
}

And that is it. Now we can call...

GetDescription(MyColor.Green)

... and we will get back the text from the description. It is just that simple.

Just for fun, let's write a method to get back our enum based on that string. Note: This might be useful for most, but imagine that we define a new attribute called [AssociatedUriAttribute] where we want to associate a URI with our enum that is unique. This opens things up quite a bit. Note: This time we will embed this in a generics based class.

public class EnumUtils<T>
{
    public static T FromDescription(string description){
        Type t = typeof(T);
        foreach (FieldInfo fi in t.GetFields())
        {
            object[] attrs = 
		fi.GetCustomAttributes(typeof(DescriptionAttribute), true);
            if (attrs != null && attrs.Length > 0)
            {
                foreach (DescriptionAttribute attr in attrs)
                {
                    if (attr.Description.Equals(description))
                        return (T)fi.GetValue(null);
                }
            }
        }
        return default(T);
}

In the end, we get a very simple class that looks like this:

using System;
using System.ComponentModel;
using System.Reflection;

/// <summary>
/// enum utilities. 
/// - converts from a [Description(&quot;&quot;)] to an enum value
/// - grabs the [Description(&quot;&quot;)] from an enum value
/// 
/// </summary>
public class EnumUtils<T>
{
    public static string GetDescription(T enumValue, string defDesc){
        
        FieldInfo fi = enumValue.GetType().GetField(enumValue.ToString());
        
        if (null != fi)
        {
            object[] attrs = fi.GetCustomAttributes
					(typeof(DescriptionAttribute), true);
            if (attrs != null && attrs.Length > 0)
                return ((DescriptionAttribute)attrs[0]).Description;
        }

        return defDesc;
    }
    
    public static string GetDescription(T enumValue)
    {
        return GetDescription(enumValue, string.Empty);
    }

    public static T FromDescription(string description){
        Type t = typeof(T);
        foreach (FieldInfo fi in t.GetFields())
        {
            object[] attrs = fi.GetCustomAttributes
					(typeof(DescriptionAttribute), true);
            if (attrs != null && attrs.Length > 0)
            {
                foreach (DescriptionAttribute attr in attrs)
                {
                    if (attr.Description.Equals(description))
                        return (T)fi.GetValue(null);
                }
            }
        }
        return default(T);
    }
}

History

• 17^th April, 2006: Initial post