is there a way to check if int is legal enum in C#

Question

I've read a few SO posts and it seems most basic operation is missing. CAN IT BE??

public enum LoggingLevel
{
    Off = 0,
    Error = 1,
    Warning = 2,
    Info = 3,
    Debug = 4,
    Trace = 5
};



if (s == "LogLevel")
{
    _log.LogLevel = (LoggingLevel)Convert.ToInt32("78");
    _log.LogLevel = (LoggingLevel)Enum.Parse(typeof(LoggingLevel), "78");
    _log.WriteDebug(_log.LogLevel.ToString());
}

no exceptions. 78 is happily wrote. this is sad. I read why the cast does not automatically throw error but PLEASE!!! NO way to check it at all. That's just too much...

Thanks & BR -Matti

Answer 1

Check out Enum.IsDefined
This is the example from that page:

using System;

[Flags] public enum PetType
{
   None = 0, Dog = 1, Cat = 2, Rodent = 4, Bird = 8, Reptile = 16, Other = 32
};

public class Example
{
   public static void Main()
   {
      object value; 

      // Call IsDefined with underlying integral value of member.
      value = 1;
      Console.WriteLine("{0}: {1}", value, Enum.IsDefined(typeof(PetType), value));
      // Call IsDefined with invalid underlying integral value.
      value = 64;
      Console.WriteLine("{0}: {1}", value, Enum.IsDefined(typeof(PetType), value));
      // Call IsDefined with string containing member name.
      value = "Rodent";
      Console.WriteLine("{0}: {1}", value, Enum.IsDefined(typeof(PetType), value));
      // Call IsDefined with a variable of type PetType.
      value = PetType.Dog;
      Console.WriteLine("{0}: {1}", value, Enum.IsDefined(typeof(PetType), value));
      value = PetType.Dog | PetType.Cat;
      Console.WriteLine("{0}: {1}", value, Enum.IsDefined(typeof(PetType), value));
      // Call IsDefined with uppercase member name.      
      value = "None";
      Console.WriteLine("{0}: {1}", value, Enum.IsDefined(typeof(PetType), value));
      value = "NONE";
      Console.WriteLine("{0}: {1}", value, Enum.IsDefined(typeof(PetType), value));
      // Call IsDefined with combined value
      value = PetType.Dog | PetType.Bird;
      Console.WriteLine("{0:D}: {1}", value, Enum.IsDefined(typeof(PetType), value));
      value = value.ToString();
      Console.WriteLine("{0:D}: {1}", value, Enum.IsDefined(typeof(PetType), value));
   }
}
// The example displays the following output:
//       1: True
//       64: False
//       Rodent: True
//       Dog: True
//       Dog, Cat: False
//       None: True
//       NONE: False
//       9: False
//       Dog, Bird: False

Answer 2

Use Enum.IsDefined.

Answer 3

Use:

Enum.IsDefined ( typeof ( Enum ), EnumValue );

Answer 4

The canonical answer would be Enum.IsDefined, but that is a: a bit slow if used in a tight loop, and b: not useful for [Flags] enums.

Personally, I'd stop worrying about that, and just switch appropriately, remembering:

• if it is OK not to recognise everything (and just not do anything), then don't add a default: (or have an empty default: explaining why)
• if there is a sensible default behaviour, put that in the default:
• otherwise, handle the ones you know about and throw an exception for the rest:

Like so:

switch(someflag) {
    case TriBool.Yes:
        DoSomething();
        break;
    case TriBool.No:
        DoSomethingElse();
        break;
    case TriBool.FileNotFound:
        DoSomethingOther();
        break;
    default:
        throw new ArgumentOutOfRangeException("someflag");
}