Typically InvalidEnumArgumentException is thrown to indicate that a value passed for a enum parameter is not a valid value for that enum's type.

You do not need to pass a message to one of InvalidEnumArgumentException's constructors that takes one; passing it the parameter name, the invalid parameter and the type of the enum causes it construct one for you along the lines of 'The value of argument '{argumentName}' ({invalidValue}) is invalid for Enum type '{enumClass}'.'

As shown in the example above, it is possible to pass a value outside of the range of an enum's allowed values. Due to this, it is advised that you validate all enum parameters. There are a number of ways to do this, with some techniques better than others. The following example shows three different methods.

C#:

public enum WeekDay
{
    Sunday = 0,
    Monday = 1,
    Tuesday = 2,
    Wednesday = 3,
    Thursday = 4,
    Friday = 5,
    Saturday = 6,
}

public static class WeekDayHelper
{
    public static bool IsWorkDay1(WeekDay day)
    {
        if (day < WeekDay.Sunday || day > WeekDay.Saturday)
            throw new InvalidEnumArgumentException("day", (int)day, typeof(WeekDay));

        return day >= WeekDay.Monday && day <= WeekDay.Friday;
    }

    public static bool IsWorkDay2(WeekDay day)
    {
        switch (day)
        {
            case WeekDay.Sunday:
            case WeekDay.Saturday:
                return false;

            case WeekDay.Monday:
            case WeekDay.Tuesday:
            case WeekDay.Wednesday:
            case WeekDay.Thursday:
            case WeekDay.Friday:
                return true;
        }

        throw new InvalidEnumArgumentException("day", (int)day, typeof(WeekDay));
    }

    // Not recommended
    public static bool IsWorkDay3(WeekDay day)
    {
        if (!Enum.IsDefined(typeof(WeekDay), day))
            throw new InvalidEnumArgumentException("day", (int)day, typeof(WeekDay));

        return day >= WeekDay.Monday && day <= WeekDay.Friday;
    }
}

 

In the first method, IsWorkDay1, the enum parameter is validated to ensure that it equal to or between the lowest valid value and the highest valid value. This has the benefit of being the cheapest, however, if during development of a product and the values of the enum changes, it could validate the values incorrectly.

The second method, IsWorkDay2, uses a switch statement to validate day. This doesn't suffer from the same problem as IsWorkDay1 (if the enum is in the same assembly) and it becomes an easy way to validate, if later in the method you are going to switch on the parameter anyway.

Although IsWorkDay3 is the simplest, it is the least recommended. Enum.IsDefined uses Reflection and rarely touched metadata to determine the valid values of the enum, and because of this, is very expensive in comparision to the other two techniques. It also suffers from a versioning issue, which is explained here: http://blogs.msdn.com/kcwalina/archive/2004/05/18/134208.aspx

Unfortunately, as InvalidEnumArgumentException is defined in System.dll and not mscorlib.dll, the latter does not throw it when an invalid enum argument is passed to a member, but instead throws ArgumentException or ArgumentOutOfRangeException. This inconsistancy however, usually does not present a problem, as this exception when thrown, typically indicates a bug in the caller and is rarely caught within a catch clause.