C# Getting Enum values

Question

I have a enum containing the following (for example):

• UnitedKingdom,
• UnitedStates,
• France,
• Portugal

In my code I use Country.UnitedKingdom but I want to have the value be UK if I assign it to a string for example.

Is this possible?

Solution 1

You can't assign an enum value to a string to start with. You'd have to call ToString(), which would convert Country.UnitedKingdom to "UnitedKingdom".

Two options suggest themselves:

• Create a Dictionary<Country, string>
• A switch statement
• Decorate each value with an attribute, and load that with reflection

Comments about each of them...

Sample code for Dictionary<Country,string>

using System;
using System.Collections.Generic;

enum Country
{
    UnitedKingdom, 
    UnitedStates,
    France,
    Portugal
}

class Test
{
    static readonly Dictionary<Country, string> CountryNames =
        new Dictionary<Country, string>
    {
        { Country.UnitedKingdom, "UK" },
        { Country.UnitedStates, "US" },
    };

    static string ConvertCountry(Country country) 
    {
        string name;
        return (CountryNames.TryGetValue(country, out name))
            ? name : country.ToString();
    }

    static void Main()
    {
        Console.WriteLine(ConvertCountry(Country.UnitedKingdom));
        Console.WriteLine(ConvertCountry(Country.UnitedStates));
        Console.WriteLine(ConvertCountry(Country.France));
    }
}

You might want to put the logic of ConvertCountry into an extension method. For example:

// Put this in a non-nested static class
public static string ToBriefName(this Country country) 
{
    string name;
    return (CountryNames.TryGetValue(country, out name))
        ? name : country.ToString();
}

Then you could write:

string x = Country.UnitedKingdom.ToBriefName();

As mentioned in the comments, the default dictionary comparer will involve boxing, which is non-ideal. For a one-off, I'd live with that until I found it was a bottleneck. If I were doing this for multiple enums, I'd write a reusable class.

Switch statement

I agree with yshuditelu's answer suggesting using a switch statement for relatively few cases. However, as each case is going to be a single statement, I'd personally change my coding style for this situation, to keep the code compact but readable:

public static string ToBriefName(this Country country) 
{
    switch (country)
    {
        case Country.UnitedKingdom:  return "UK";
        case Country.UnitedStates:   return "US";
        default:                     return country.ToString();
    }
}

You can add more cases to this without it getting too huge, and it's easy to cast your eyes across from enum value to the return value.

DescriptionAttribute

The point Rado made about the code for DescriptionAttribute being reusable is a good one, but in that case I'd recommend against using reflection every time you need to get a value. I'd probably write a generic static class to hold a lookup table (probably a Dictionary, possibly with a custom comparer as mentioned in the comments). Extension methods can't be defined in generic classes, so you'd probably end up with something like:

public static class EnumExtensions
{
    public static string ToDescription<T>(this T value) where T : struct
    {
        return DescriptionLookup<T>.GetDescription(value);
    }

    private static class DescriptionLookup<T> where T : struct
    {
        static readonly Dictionary<T, string> Descriptions;

        static DescriptionLookup()
        {
            // Initialize Descriptions here, and probably check
            // that T is an enum
        }

        internal static string GetDescription(T value)
        {
            string description;
            return Descriptions.TryGetValue(value, out description)
                ? description : value.ToString();
        }
    }
}

Solution 2

I prefer to use the DescriptionAttribute on my enums. Then, you can use the following code to grab that description from the enum.

enum MyCountryEnum
{    
    [Description("UK")]
    UnitedKingdom = 0,    

    [Description("US")]
    UnitedStates = 1,    

    [Description("FR")]
    France = 2,    

    [Description("PO")]
    Portugal = 3
}

public static string GetDescription(this Enum value)
{
    var type = value.GetType();

    var fi = type.GetField(value.ToString());

    var descriptions = fi.GetCustomAttributes(typeof(DescriptionAttribute), false) as DescriptionAttribute[];

    return descriptions.Length > 0 ? descriptions[0].Description : value.ToString();
}

public static SortedDictionary<string, T> GetBoundEnum<T>() where T : struct, IConvertible
{
    // validate.
    if (!typeof(T).IsEnum)
    {
        throw new ArgumentException("T must be an Enum type.");
    }

    var results = new SortedDictionary<string, T>();

    FieldInfo[] fieldInfos = typeof(T).GetFields();

    foreach (var fi in fieldInfos)
    {

        var value = (T)fi.GetValue(fi);
        var description = GetDescription((Enum)fi.GetValue(fi));

        if (!results.ContainsKey(description))
        {
            results.Add(description, value);
        }
    }
    return results;
}

And then to get my bound enum list, its simply a call to

GetBoundEnum<MyCountryEnum>()

To get a single enum's description, you'd just use the extension method like this

string whatever = MyCountryEnum.UnitedKingdom.GetDescription();

Solution 3

You could create an extension method public static string ToShortString(this Country country). In the method you could use either a static Dictionary as Jon suggests, or you could simply do a switch case.

Example:

public static class CountryExtensions
{
    public static string ToShortString( this Country target )
    {
        switch (target) {
            case Country.UnitedKingdom:
                return "UK";
            case Country.UnitedStates:
                return "US";
            case Country.France:
                return "FR";
            case Country.Portugal:
                return "PT";
            default:
                return "None";
        }
    }
}

Solution 4

Pseudo code:

enum MyCountryEnum
{
    UnitedKingdom = 0,
    UnitedStates = 1,
    France = 2,
    Portugal = 3,
}

string[] shortCodes = new string[] {"UK", "US", "FR", "PO"};


MyCountryEnum enumValue = MyCountryEnum.UnitedKingdom;
string code = shortCodes[enumValue];

Solution 5

One other possibility that hasn't been mentioned is something like this:

public class Country
{
    public static readonly Country UnitedKingdom = new Country("UK");
    public static readonly Country UnitedStates = new Country("US");
    public static readonly Country France = new Country("FR");
    public static readonly Country Protugal = new Country("PT");

    private Country(string shortName)
    {
        ShortName = shortName;
    }

    public string ShortName { get; private set; }
}

From this point you could add more properties, but beware of how much you add to the class, and how many static members you add, as the memory bloat it adds could make it not worth it.

I don't think there are many cases where this strategy is the best approach, but it is an option to be aware of when attempting to add properties or attributes to something you want to be able to treat as essentially an enum.

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