Reading the DescriptionAttribute of enumerators and returning the corresponding enum based on the description

by Heathesh 24. May 2010 01:36

There are two things I wanted to achieve using the DescriptionAttribute for my enumerators. The first was to retrieve the description of an enumerator using an extension method, and the second was to return the relevant enumerator based on the description.

To begin with I created a static class I called EnumExtensionManager. I wanted to add my two methods as extension methods so hence the need for the static class. The very first thing I did was apply the description attribute to my enum definitions as follows:

    /// <summary>
    /// Enum of the regions
    /// </summary>
    public enum Region
    {
        [Description("All")]
        AllRegions = 0,
        [Description("Gauteng")]
        Gauteng = 1,
        [Description("Free State")]
        FreeState = 2,
        [Description("Eastern Cape")]
        EasternCape = 3,
        [Description("Western Cape")]
        WesternCape = 4,
        [Description("Mpumalanga")]
        Mpumalanga = 5,
        [Description("Northern Cape")]
        NorthernCape = 6,
        [Description("North West")]
        NorthWest = 7,
        [Description("KwaZulu-Natal")]
        KwaZuluNatal = 8,
        [Description("Limpopo")]
        Limpopo = 9
    }


Now, in order to retrieve the description of the enumerator I created the following static method in my EnumExtensionManager class:

        /// <summary>
        /// Gets the description of an enumerator
        /// </summary>
        /// <param name="enumerator"></param>
        /// <returns></returns>
        public static string GetDescription(this Enum enumerator)
        {
            //get the enumerator type
            Type type = enumerator.GetType();

            //get the member info
            MemberInfo[] memberInfo = type.GetMember(enumerator.ToString());

            //if there is member information
            if (memberInfo != null && memberInfo.Length > 0)
            {
                //we default to the first member info, as it's for the specific enum value
                object[] attributes = memberInfo[0].GetCustomAttributes(typeof(DescriptionAttribute), false);

                //return the description if it's found
                if (attributes != null && attributes.Length > 0)
                    return ((DescriptionAttribute)attributes[0]).Description;
            }

            //if there's no description, return the string value of the enum
            return enumerator.ToString();
        }


The method will return the description text for an enumerator or return the enumerator name as a string if it can't find the description. Since I created it as an extension method, it was easy enough to call it in code simply by invoking .GetDescription() on any enum value.

            Region regionEnumerator = Region.KwaZuluNatal;
            string regionDescription = regionEnumerator.GetDescription();


Next I wanted to be able to use the description of an enum and return the corresponding enum from it. I achieved this by adding the following extension method to me EnumExtensionManager class:

        /// <summary>
        /// Gets the enumerator from the description passed in
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="description"></param>
        /// <returns></returns>
        public static T GetEnumFromDescription<T>(this string description)
        {
            //get the member info of the enum
            MemberInfo[] memberInfos = typeof(T).GetMembers();

            if (memberInfos != null && memberInfos.Length > 0)
            {
                //loop through the member info classes
                foreach (MemberInfo memberInfo in memberInfos)
                {
                    //get the custom attributes of the member info
                    object[] attributes = memberInfo.GetCustomAttributes(typeof(DescriptionAttribute), false);

                    //if there are attributes
                    if (attributes != null && attributes.Length > 0)
                        //if the description attribute is equal to the description, return the enum
                        if (((DescriptionAttribute)attributes[0]).Description == description)
                            return (T)Enum.Parse(typeof(T), memberInfo.Name);
                }
            }

            //this means the enum was not found from the description, so return the default
            return default(T);
        }


Calling the method was easily done and it could be invoked on any string value like so:

            string regionDescription = "Northern Cape";
            Region regionEnumerator = regionDescription.GetEnumFromDescription<Region>();


That was it. Happy enumerating!

 

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