Question

I have multiple flags enums defined in code similar to the following

[Flags]
public enum Colors
{
   None = 0,
   Red = 1,
   Green = 2,
   Blue = 4, 
   Purple = Red | Blue,
   Brown = Red | Green,
}

The following code produces the following output

Colors color1 = Colors.Red | Colors.Blue;
Colors color2 = Colors.Purple;
string s1 = color1.ToString(); // Sets s1 to "Purple"
string s2 = color2.ToString(); // Sets s2 to "Purple"

I want a method that outputs the individual bits of a bitwise enum, even if a matching combination is defined.

private void Foo()
{
  Colors color1 = Colors.Red | Colors.Blue;
  Colors color2 = Colors.Purple;
  string s1 = CreateColumnString(color1); // Sets s1 to "Red|Blue"
  string s2 = CreateColumnString(color2); // Sets s2 to "Red|Blue"
}

I thought I could loop through all the values of an enum and check if the value is a power of two. But I can’t figure out how to get the underlying value of the Enum argument.

private string CreateColumnString(object value)
{
 //is this an enum with Flags attribute?
 if (value is Enum  && value.GetType().GetCustomAttributes(typeof(FlagsAttribute), true).Length > 0)
 {
    Enum e = (Enum)value;
    //Get a list of Enum values set in this flags enum
    IEnumerable<Enum> setValues = 
      Enum.GetValues(value.GetType())
          .Cast<Enum>()
          .Where(eachEnum => IsPowerOfTwo(eachEnum) && value.HasFlag(eachEnum)); 

    return string.Join("|", setValues);
 }
 else
 {
    return value != null ? value.ToString() : string.Empty;
 }
 return str;
}

private static bool IsPowerOfTwo(Enum e)
{
   int x = (int)e; //ERROR cannot convert type 'System.Enum' to 'ulong'
   return (x != 0) && ((x & (x - 1)) == 0);
}

Answer 1

Here’s another approach. I figure the more options you have, the better 🙂

public static class EnumHelpers
{
    public static string ToStringExtended<T>(this Enum e)
    {
        if (!(e.GetType().GetCustomAttributes(typeof(FlagsAttribute), true).Length > 0))
            return e.ToString();

        List<string> eNames = new List<string>();
        foreach (T fish in Enum.GetValues(typeof(T)))
        {
            Enum num = fish as Enum;
            if (e.HasFlag(num) && Convert.ToInt32(fish) != 0 && Convert.ToInt32(fish) != Convert.ToInt32(e))
                eNames.Add(fish.ToString());
        }

        return eNames.Count > 1 ? String.Join("|", eNames.ToArray()) : e.ToString();
    }
}

The usage is almost identical to what Fredirk proposed:

Colors c = Colors.Purple;
Console.WriteLine(c.ToStringExtended<Colors>());
// Output : Red|Blue