How to determine if a given Integer is in a particular Enum?

Question

In VB.NET, even with Option Strict on, it\'s possible to pass an Enum around as an Integer.

In my particular situation, someone\'s using an enum similar to

Answer 1

Although .NET 4.0 introduced the Enum.TryParse method you should not use it for this specific scenario. In .NET an enumeration has an underlying type which can be any of the following (byte, sbyte, short, ushort, int, uint, long, or ulong). By default is int, so any value that is a valid int is also a valid enumeration value.

This means that Enum.TryParse("-1", out result) reports success even though -1 is not associated to any specified enumeration value.

As other have noted, for this scenarios, you must use Enum.IsDefined method.

Sample code (in C#):

enum Test { Zero, One, Two }

static void Main(string[] args)
{
    Test value;
    bool tryParseResult = Enum.TryParse("-1", out value);
    bool isDefinedResult = Enum.IsDefined(typeof(Test), -1);

    Console.WriteLine("TryParse: {0}", tryParseResult); // True
    Console.WriteLine("IsDefined: {0}", isDefinedResult); // False
}