Question

I’m having difficulties working with some legacy enums that have multiple zero values. Whenever I call ToString on one of the non-zero values, all but the first zero value is included.

Is there any way to isolate the non-zero value name without resorting to string manipulation or reflection?

//all of the following output "Nada, Zilch, One"
Console.WriteLine(TestEnum.One);
Console.WriteLine(Convert.ToString(TestEnum.One));
Console.WriteLine(TypeDescriptor.GetConverter(typeof(TestEnum))
                      .ConvertToString(TestEnum.One));

[Flags]
enum TestEnum
{
    Zero = 0,
    Nada = 0,
    Zilch = 0,
    One = 1
}

Edit

I understand that having multiple items with the same value is not recommended however the enum in question is defined in a legacy assembly that I can’t change. In fact, there are 12 public enums in mscorlib v4 that break this recommendation, as determined by the following simple LINQ query:

var types = typeof (void).Assembly.GetTypes()
    .Where(type => type.IsEnum &&
                   type.IsPublic &&
                   Enum.GetValues(type).Cast<object>()
                       .GroupBy(value => value)
                       .Any(grp => grp.Count() > 1))
    .ToList();

Answer 1

Here is one option. It works, but it’s a bit ugly. The values / names variables won’t change, so they only need to be calculated once.

Assuming you have a slightly more complicated enum, such as:

[Flags]
public enum TestEnum
{
    Zero = 0,
    Nada = 0,
    Zilch = 0,
    One = 1,
    Two = 2,
    Three = 3,
    Four = 4
}

Here is some code you could use:

var input = TestEnum.One | TestEnum.Two;
var values = (TestEnum[]) Enum.GetValues(typeof (TestEnum));
var names = Enum.GetNames(typeof (TestEnum));
var result = values
    .Select((value, index) =>
            input == value || (value != 0 && (input & value) == value)
                ? names[index]
                : null)
    .Where(name => name != null);
var text = string.Join(", ", result);
Console.WriteLine(text);