Question

I generate dynamic enums that represent integer IDs from my database in a C# ASP.NET solution. I would like two things, although neither may be possible.

1) I want the .ToString() method to give me “345” for example, not the string name of the enum (the int it represents as a string). Every answer to this question seems to be adding

[Description="Blah"]
EnumName = 1

above the declaration and using a GetDescription() method. I have no idea how to do this with the dynamic code that I am using.

2) I’d rather not cast to an int to use it as such, I’d rather (Enum.Name == 5) for example. If this isn’t possible I’ll cast, but I really don’t want to use ((int)Enum.Name)).ToString();

Here’s the dynamic code generation:

public static void Main()
{
    AppDomain domain = AppDomain.CurrentDomain;

    AssemblyName aName = new AssemblyName("DynamicEnums");
    AssemblyBuilder ab = domain.DefineDynamicAssembly(aName, AssemblyBuilderAccess.Save);

    ModuleBuilder mb = ab.DefineDynamicModule(aName.Name, aName.Name + ".dll");

    List<Type> types = new List<Type>();

    foreach(ReferenceType rt in GetTypes())
    {
        EnumBuilder eb = mb.DefineEnum(rt.Name, TypeAttributes.Public, typeof(int));

        foreach (Reference r in GetReferences(rt.ID))
        {
            eb.DefineLiteral(NameFix(r.Name), r.ID);
        }

        types.Add(eb.CreateType());
    }

    ab.Save(aName.Name + ".dll");

    foreach (Type t in types)
    {
        foreach (object o in Enum.GetValues(t))
        {
            Console.WriteLine("{0}.{1} = {2}", t, o, ((int) o));
        }

        Console.WriteLine();
        //Console.ReadKey();
    }

    Console.WriteLine();
    Console.WriteLine("Dynamic Enums Built Successfully.");
}

public static string NameFix(string name)
{
    //Strip all non alphanumeric characters
    string r = Regex.Replace(name, @"[^\w]", "");

    //Enums cannot begin with a number
    if (Regex.IsMatch(r, @"^\d"))
        r = "N" + r;

    return r;
}

There may just be no way to do what I want to do, and I’ll be stuck using:

(int)Countries.USA //For int value
((int)Countries.CAN).ToString() //For string representation of int value, ex. "354"

Any ideas?

Answer 1

Could you adapt the type-safe enum pattern to do what you need?

public class MyEnum
{
    #region Enum Values

    // Pre defined values.    
    public static readonly MyEnum ValueOne = new MyEnum(0);
    public static readonly MyEnum ValueTwo = new MyEnum(1);

    // All values in existence.
    private static readonly Dictionary<int, MyEnum> existingEnums = new Dictionary<int, MyEnum>{{ValueOne.Value, ValueOne}, {ValueTwo.Value, ValueTwo}};

    #endregion

    #region Enum Functionality

    private readonly int Value;

    private MyEnum(int value)
    {
        Value = value;
    }

    public static MyEnum GetEnum(int value)
    {
        // You will probably want to make this thread-safe.
        if (!existingEnums.ContainsKey(value)) existingEnums[value] = new MyEnum(value);

        return existingEnums[value];
    }

    public override string ToString()
    {
        return Value.ToString();
    }

    #endregion
}

Usage:

private void Foo(MyEnum enumVal)
{
  return "Enum Value: " + enumVal;  // returns "Enum Value: (integer here) 
}

Or:

MyEnum.GetValue(2) == MyEnum.GetValue(4); // false
MyEnum.GetValue(3) == MyEnum.GetValue(3); // true