How do you pass multiple enum values in C#?

Question

Sometimes when reading others\' C# code I see a method that will accept multiple enum values in a single parameter. I always thought it was kind of neat, but never looked in

Answer 1

With the help of the posted answers and these:

1. FlagsAttribute Class (Look at the comparison of using and not using the [Flags] attribute)
2. Enum Flags Attribute

I feel like I understand it pretty well.

Thanks.

Answer 2

I second Reed's answer. However, when creating the enum, you must specify the values for each enum member so it makes a sort of bit field. For example:

[Flags]
public enum DaysOfWeek
{
    Sunday = 1,
    Monday = 2,
    Tuesday = 4,
    Wednesday = 8,
    Thursday = 16,
    Friday = 32,
    Saturday = 64,

    None = 0,
    All = Weekdays | Weekend,
    Weekdays = Monday | Tuesday | Wednesday | Thursday | Friday,
    Weekend = Sunday | Saturday,
    // etc.
}

Answer 3

In my particular situation, I would like to use the System.DayOfWeek

You can not use the System.DayOfWeek as a [Flags] enumeration because you have no control over it. If you wish to have a method that accepts multiple DayOfWeek then you will have to use the params keyword

void SetDays(params DayOfWeek[] daysToSet)
{
    if (daysToSet == null || !daysToSet.Any())
        throw new ArgumentNullException("daysToSet");

    foreach (DayOfWeek day in daysToSet)
    {
        // if( day == DayOfWeek.Monday ) etc ....
    }
}

SetDays( DayOfWeek.Monday, DayOfWeek.Sunday );

Otherwise you can create your own [Flags] enumeration as outlined by numerous other responders and use bitwise comparisons.

Answer 4

Reed Copsey is correct and I would add to the original post if I could, but I cant so I'll have to reply instead.

Its dangerous to just use [Flags] on any old enum. I believe you have to explicitly change the enum values to powers of two when using flags, to avoid clashes in the values. See the guidelines for FlagsAttribute and Enum.