Stefan's ASP.NET Blog

Hello again,
 

I am currently making a Virtual Earth asp.net ajax server control and came to the point where I had to replicate the enums in my classes, but the issue with them is that the enums do not use integer values but string ones. In C# you cannot have an enum that has string values :(. So the solution I came up with (I am sure it has been done before) was just to make a new custom attribute called StringValueAttribute and use this to give values in my enum a string based value.

Note: All code here was written using .NET 3.5 and I am using 3.5 specific features like automatic properties and exension methods, this could be rewritten to suit 2.0 quite easily.


First I created the new custom attribute class, the source is below:

    /// <summary>
    /// This attribute is used to represent a string value
    /// for a value in an enum.
    /// </summary>
    public class StringValueAttribute : Attribute {

        #region Properties

        /// <summary>
        /// Holds the stringvalue for a value in an enum.
        /// </summary>
        public string StringValue { get; protected set; }

        #endregion

        #region Constructor

        /// <summary>
        /// Constructor used to init a StringValue Attribute
        /// </summary>
        /// <param name="value"></param>
        public StringValueAttribute(string value) {
            this.StringValue = value;
        }

        #endregion

    }

 
Then I created a new Extension Method which I will use to get the string value for an enums value:

        /// <summary>
        /// Will get the string value for a given enums value, this will
        /// only work if you assign the StringValue attribute to
        /// the items in your enum.
        /// </summary>
        /// <param name="value"></param>
        /// <returns></returns>
        public static string GetStringValue(this Enum value) {
            // Get the type
            Type type = value.GetType();

            // Get fieldinfo for this type
            FieldInfo fieldInfo = type.GetField(value.ToString());

            // Get the stringvalue attributes
            StringValueAttribute[] attribs = fieldInfo.GetCustomAttributes(
                typeof(StringValueAttribute), false) as StringValueAttribute[];

            // Return the first if there was a match.
            return attribs.Length > 0 ? attribs[0].StringValue : null;
        }
 

So now create your enum and add the StringValue attributes to your values:

 public enum Test : int {
        [StringValue("a")]
        Foo = 1,
        [StringValue("b")]
        Something = 2       
 }


Now you are ready to go, to get the string value for a value in the enum you can do so like this now:

Test t = Test.Foo;
string val = t.GetStringValue();

- or even -

string val = Test.Foo.GetStringValue();



All this is very easy to implement and I like the ease of use you get from the extension method [I really like them :)] and it gave me the power I needed to do what I needed. I haven't tested the performance hit that the reflection may give and might do so sometime soon.


Thanks
Stefan