String representation of an Enum

Question

I have the following enumeration:

public enum AuthenticationMethod
{
    FORMS = 1,
    WINDOWSAUTHENTICATION = 2,
    SINGLESIGNON = 3
}

The problem however is that I need the word "FORMS" when I ask for AuthenticationMethod.FORMS and not the id 1.

I have found the following solution for this problem (link):

First I need to create a custom attribute called "StringValue":

public class StringValue : System.Attribute
{
    private readonly string _value;

    public StringValue(string value)
    {
        _value = value;
    }

    public string Value
    {
        get { return _value; }
    }

}

Then I can add this attribute to my enumerator:

public enum AuthenticationMethod
{
    [StringValue("FORMS")]
    FORMS = 1,
    [StringValue("WINDOWS")]
    WINDOWSAUTHENTICATION = 2,
    [StringValue("SSO")]
    SINGLESIGNON = 3
}

And of course I need something to retrieve that StringValue:

public static class StringEnum
{
    public static string GetStringValue(Enum value)
    {
        string output = null;
        Type type = value.GetType();

        //Check first in our cached results...

        //Look for our 'StringValueAttribute' 

        //in the field's custom attributes

        FieldInfo fi = type.GetField(value.ToString());
        StringValue[] attrs =
           fi.GetCustomAttributes(typeof(StringValue),
                                   false) as StringValue[];
        if (attrs.Length > 0)
        {
            output = attrs[0].Value;
        }

        return output;
    }
}

Good now I've got the tools to get a string value for an enumerator. I can then use it like this:

string valueOfAuthenticationMethod = StringEnum.GetStringValue(AuthenticationMethod.FORMS);

Okay now all of these work like a charm but I find it a whole lot of work. I was wondering if there is a better solution for this.

I also tried something with a dictionary and static properties but that wasn't better either.

Answer 1

I agree with Keith, but I can't vote up (yet).

I use a static method and swith statement to return exactly what I want. In the database I store tinyint and my code only uses the actual enum, so the strings are for UI requirements. After numerous testing this resulted in the best performance and most control over the output.

public static string ToSimpleString(this enum)
{
     switch (enum)
     {
         case ComplexForms:
             return "ComplexForms";
             break;
     }
}

public static string ToFormattedString(this enum)
{
     switch (enum)
     {
         case ComplexForms:
             return "Complex Forms";
             break;
     }
}

However, by some accounts, this leads to a possible maintenance nightmare and some code smell. I try to keep an eye for enums that are long and a lot of enums, or those that change frequently. Otherwise, this has been a great solution for me.

Answer 2

A lot of great answers here but in my case did not solve what I wanted out of an "string enum", which was:

1. Usable in a switch statement e.g switch(myEnum)
2. Can be used in function parameters e.g. foo(myEnum type)
3. Can be referenced e.g. myEnum.FirstElement
4. I can use strings e.g. foo("FirstElement") == foo(myEnum.FirstElement)

1,2 & 4 can actually be solved with a C# Typedef of a string (since strings are switchable in c#)

3 can be solved by static const strings. So if you have the same needs, this is the simplest approach:

public sealed class Types
{

    private readonly String name;

    private Types(String name)
    {
        this.name = name;

    }

    public override String ToString()
    {
        return name;
    }

    public static implicit operator Types(string str)
    {
        return new Types(str);

    }
    public static implicit operator string(Types str)
    {
        return str.ToString();
    }


    #region enum

    public const string DataType = "Data";
    public const string ImageType = "Image";
    public const string Folder = "Folder";
    #endregion

}

This allows for example:

    public TypeArgs(Types SelectedType)
    {
        Types SelectedType = SelectedType
    }

and

public TypeObject CreateType(Types type)
    {
        switch (type)
        {

            case Types.ImageType:
              //
                break;

            case Types.DataType:
             //
                break;

        }
    }

Where CreateType can be called with a string or a type. However the downside is that any string is automatically a valid enum, this could be modified but then it would require some kind of init function...or possibly make they explicit cast internal?

Now if an int value was important to you (perhaps for comparison speed), you could use some ideas from Jakub Šturc fantastic answer and do something a bit crazy, this is my stab at it:

    public sealed class Types
{
    private static readonly Dictionary<string, Types> strInstance = new Dictionary<string, Types>();
    private static readonly Dictionary<int, Types> intInstance = new Dictionary<int, Types>();

    private readonly String name;
    private static int layerTypeCount = 0;
    private int value;
    private Types(String name)
    {
        this.name = name;
        value = layerTypeCount++;
        strInstance[name] = this;
        intInstance[value] = this;
    }

    public override String ToString()
    {
        return name;
    }


    public static implicit operator Types(int val)
    {
        Types result;
        if (intInstance.TryGetValue(val, out result))
            return result;
        else
            throw new InvalidCastException();
    }

    public static implicit operator Types(string str)
    {
        Types result;
        if (strInstance.TryGetValue(str, out result))
        {
            return result;
        }
        else
        {
            result = new Types(str);
            return result;
        }

    }
    public static implicit operator string(Types str)
    {
        return str.ToString();
    }

    public static bool operator ==(Types a, Types b)
    {
        return a.value == b.value;
    }
    public static bool operator !=(Types a, Types b)
    {
        return a.value != b.value;
    }

    #region enum

    public const string DataType = "Data";
    public const string ImageType = "Image";

    #endregion

}

but of course "Types bob = 4;" would be meaningless unless you had initialized them first which would sort of defeat the point...

But in theory TypeA == TypeB would be quicker...

Answer 3

based on the MSDN: http://msdn.microsoft.com/en-us/library/cc138362.aspx

foreach (string str in Enum.GetNames(typeof(enumHeaderField)))
{
    Debug.WriteLine(str);
}

str will be the names of the fields

Answer 4

When I am in a situation like that I propose the solution below.

And as a consuming class you could have

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace MyApp.Dictionaries
{
    class Greek
    {

        public static readonly string Alpha = "Alpha";
        public static readonly string Beta = "Beta";
        public static readonly string Gamma = "Gamma";
        public static readonly string Delta = "Delta";


        private static readonly BiDictionary<int, string> Dictionary = new BiDictionary<int, string>();


        static Greek() {
            Dictionary.Add(1, Alpha);
            Dictionary.Add(2, Beta);
            Dictionary.Add(3, Gamma);
            Dictionary.Add(4, Delta);
        }

        public static string getById(int id){
            return Dictionary.GetByFirst(id);
        }

        public static int getByValue(string value)
        {
            return Dictionary.GetBySecond(value);
        }

    }
}

And using a bidirectional dictionary: Based on this (https://stackoverflow.com/a/255638/986160) assuming that the keys will be associated with single values in the dictionary and similar to (https://stackoverflow.com/a/255630/986160) but a bit more elegant. This dictionary is also enumerable and you can go back and forth from ints to strings. Also you don't have to have any string in your codebase with the exception of this class.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Collections;

namespace MyApp.Dictionaries
{

    class BiDictionary<TFirst, TSecond> : IEnumerable
    {
        IDictionary<TFirst, TSecond> firstToSecond = new Dictionary<TFirst, TSecond>();
        IDictionary<TSecond, TFirst> secondToFirst = new Dictionary<TSecond, TFirst>();

        public void Add(TFirst first, TSecond second)
        {
            firstToSecond.Add(first, second);
            secondToFirst.Add(second, first);
        }

        public TSecond this[TFirst first]
        {
            get { return GetByFirst(first); }
        }

        public TFirst this[TSecond second]
        {
            get { return GetBySecond(second); }
        }

        public TSecond GetByFirst(TFirst first)
        {
            return firstToSecond[first];
        }

        public TFirst GetBySecond(TSecond second)
        {
            return secondToFirst[second];
        }

        public IEnumerator GetEnumerator()
        {
            return GetFirstEnumerator();
        }

        public IEnumerator GetFirstEnumerator()
        {
            return firstToSecond.GetEnumerator();
        }

        public IEnumerator GetSecondEnumerator()
        {
            return secondToFirst.GetEnumerator();
        }
    }
}

Answer 5

As most of you, I really liked the selected answer by Jakub Šturc, but I also really hate to copy-paste code, and try to do it as little as I can.

So I decided I wanted an EnumBase class from which most of the functionality is inherited/built-in, leaving me to focus on the content instead of behavior.

The main problem with this approach is based on the fact that although Enum values are type-safe instances, the interaction is with the Static implementation of the Enum Class type. So with a little help of generics magic, I think I finally got the correct mix. Hope someone finds this as useful as I did.

I'll start with Jakub's example, but using inheritance and generics:

public sealed class AuthenticationMethod : EnumBase<AuthenticationMethod, int>
{
    public static readonly AuthenticationMethod FORMS =
        new AuthenticationMethod(1, "FORMS");
    public static readonly AuthenticationMethod WINDOWSAUTHENTICATION =
        new AuthenticationMethod(2, "WINDOWS");
    public static readonly AuthenticationMethod SINGLESIGNON =
        new AuthenticationMethod(3, "SSN");

    private AuthenticationMethod(int Value, String Name)
        : base( Value, Name ) { }
    public new static IEnumerable<AuthenticationMethod> All
    { get { return EnumBase<AuthenticationMethod, int>.All; } }
    public static explicit operator AuthenticationMethod(string str)
    { return Parse(str); }
}

And here is the base class:

using System;
using System.Collections.Generic;
using System.Linq; // for the .AsEnumerable() method call

// E is the derived type-safe-enum class
// - this allows all static members to be truly unique to the specific
//   derived class
public class EnumBase<E, T> where E: EnumBase<E, T>
{
    #region Instance code
    public T Value { get; private set; }
    public string Name { get; private set; }

    protected EnumBase(T EnumValue, string Name)
    {
        Value = EnumValue;
        this.Name = Name;
        mapping.Add(Name, this);
    }

    public override string ToString() { return Name; }
    #endregion

    #region Static tools
    static private readonly Dictionary<string, EnumBase<E, T>> mapping;
    static EnumBase() { mapping = new Dictionary<string, EnumBase<E, T>>(); }
    protected static E Parse(string name)
    {
        EnumBase<E, T> result;
        if (mapping.TryGetValue(name, out result))
        {
            return (E)result;
        }

        throw new InvalidCastException();
    }
    // This is protected to force the child class to expose it's own static
    // method.
    // By recreating this static method at the derived class, static
    // initialization will be explicit, promising the mapping dictionary
    // will never be empty when this method is called.
    protected static IEnumerable<E> All
    { get { return mapping.Values.AsEnumerable().Cast<E>(); } }
    #endregion
}

Answer 6

Well, after reading all of the above I feel that the guys have over complicated the issue of transforming enumerators into strings. I liked the idea of having attributes over enumerated fields but i think that attributes are mainly used for Meta-data, but in your case i think that all you need is some sort of localization.

public enum Color 
{ Red = 1, Green = 2, Blue = 3}


public static EnumUtils 
{
   public static string GetEnumResourceString(object enumValue)
    {
        Type enumType = enumValue.GetType();
        string value = Enum.GetName(enumValue.GetType(), enumValue);
        string resourceKey = String.Format("{0}_{1}", enumType.Name, value);
        string result = Resources.Enums.ResourceManager.GetString(resourceKey);
        if (string.IsNullOrEmpty(result))
        {
            result = String.Format("{0}", value);
        }
        return result;
    }
}

Now if we try to call the above method we can call it this way

public void Foo()
{
  var col = Color.Red;
  Console.WriteLine (EnumUtils.GetEnumResourceString (col));
}

All you need to do is just create a resource file containing all the enumerator values and the corresponding strings

Resource Name          Resource Value
Color_Red              My String Color in Red
Color_Blue             Blueeey
Color_Green            Hulk Color

What is actually very nice about that is that it will be very helpful if you need your application to be localized, since all you need to do is just create another resource file with your new language! and Voe-la!