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 into it.

Well, now I think I may have a need for it, but don't know how to

set up the method signature to accept this
work with the values in the method
define the enum

to achieve this sort of thing.

In my particular situation, I would like to use the System.DayOfWeek, which is defined as:

[Serializable]
[ComVisible(true)]
public enum DayOfWeek
{ 
    Sunday = 0,   
    Monday = 1,   
    Tuesday = 2,   
    Wednesday = 3,   
    Thursday = 4,   
    Friday = 5,    
    Saturday = 6
}

I want to be able to pass one or more of the DayOfWeek values to my method. Will I be able to use this particular enum as it is? How do I do the 3 things listed above?

As mentioned below, you can use a Flags enum. You may want to check out [The ins and outs of C# enums](http://www.codeducky.org/ins-outs-c-enums/), which contains more information on working with Flags enums. — ChaseMedallion, Jul 20 '14 at 20:13

Reed Copsey · Accepted Answer · 2009-06-23T01:05:40.240

210

When you define the enum, just attribute it with [Flags], set values to powers of two, and it will work this way.

Nothing else changes, other than passing multiple values into a function.

For example:

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

public void RunOnDays(DaysOfWeek days)
{
   bool isTuesdaySet = (days & DaysOfWeek.Tuesday) == DaysOfWeek.Tuesday;

   if (isTuesdaySet)
      //...
   // Do your work here..
}

public void CallMethodWithTuesdayAndThursday()
{
    this.RunOnDays(DaysOfWeek.Tuesday | DaysOfWeek.Thursday);
}

For more details, see MSDN's documentation on Enumeration Types.

Edit in response to additions to question.

You won't be able to use that enum as is, unless you wanted to do something like pass it as an array/collection/params array. That would let you pass multiple values. The flags syntax requires the Enum to be specified as flags (or to bastardize the language in a way that's its not designed).

edited Jun 23 '09 at 01:05

answered Jun 23 '09 at 00:41

Reed Copsey

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I think if you want this to work, the values need to be defined as powers of two, a single bit for each value. What happens is that you pass in the bitwise OR of the values in the parameter, that you can check using bitwise AND operations. If you do not take care of defining the values as, for example, 1,2,4,8 etc, you will have problems. – Denis Troller Jun 23 '09 at 00:54
1

Just setting Flags attribute alone doesn't work automatically. I just tried it. – Richard Anthony Hein Jun 23 '09 at 01:03
1

You're right, and I removed the misinformation. Fixed up Reed's code too for him. – Matthew Scharley Jun 23 '09 at 01:07
@monoxide: I fixed it at the same time - sorry about overriding your edits. – Reed Copsey Jun 23 '09 at 01:08
2

No problem... I still prefer using hex for flag values like that, seems more clear to me, but each to his own. – Matthew Scharley Jun 23 '09 at 01:10
@monoxide: Hex is useful for that, too - especially if you're going to have many elements in your enumerator. Good point. It's a style/personal preference thing, though. – Reed Copsey Jun 23 '09 at 01:12
I think the cleaner solution is to use HasFlag(...) which is new in Framework 4.0. See my solution further down. – Tillito Apr 13 '11 at 23:58
@Tillito: Yes, this predated .NET 4 by a long margin, so Enum.HasFlag didn't exist at the time. – Reed Copsey Apr 14 '11 at 00:06

score 88 · Answer 2 · answered Apr 13 '11 at 23:56

88

I think the more elegant solution is to use HasFlag():

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

    public void RunOnDays(DaysOfWeek days)
    {
        bool isTuesdaySet = days.HasFlag(DaysOfWeek.Tuesday);

        if (isTuesdaySet)
        {
            //...
        }
    }

    public void CallMethodWithTuesdayAndThursday()
    {
        RunOnDays(DaysOfWeek.Tuesday | DaysOfWeek.Thursday);
    }

answered Apr 13 '11 at 23:56

Tillito

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There is another important thing to know, if you do it this way: It adds much more flexibility when you need to fill your enum dynamically. E.g.: If you use checkboxes to define the days, on which you want your program to run, and you would try to accomplish this in the way its done above, the code will be unreadable. So instead you can do it this way: ... `DaysOfWeek days = new DaysOfWeek(); if (cbTuesday.Checked) days |= DaysOfWeek.Tuesday; if (cbWednesday.Checked) days |= DaysOfWeek.Wednesday;` ... – CoastN Jul 31 '19 at 07:29

Jacob · Answer 3 · 2009-06-23T01:06:46.573

34

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.
}

edited Jun 23 '09 at 01:06

answered Jun 23 '09 at 00:46

Jacob

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It will help you if you ever need to inspect a DaysOfWeek value, for example if you're reading one that's stored in a database. Also, it provides better documentation to other programmers, since some enumerate days of the week starting from Monday instead of Sunday. – Jacob Jun 23 '09 at 00:56
3

For clarity and maintainability, I would write your 'All' enum as "Sunday|Monday|Tuesday|Wednesday|Thursday|Friday|Saturday"... and use a similar notation for 'Weekdays' and 'Weekend'. – Robert Cartaino Jun 23 '09 at 00:57
This is fine if you want to create your own enum, but to answer the question you cannot alter the existing DaysOfWeek enum – Robert Paulson Jun 23 '09 at 01:02
2

Not "may want to" ... you MUST. Bitwise comparisons requires it. Leaving the values unspecified will not work. – Richard Anthony Hein Jun 23 '09 at 01:07

score 17 · Answer 4 · answered Jun 23 '09 at 02:11

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.

I don't know why I didn't think of params. That should be very useful for using enums that aren't bitfields. — Ronnie Overby, Jun 23 '09 at 17:04

score 14 · Answer 5 · answered Jun 23 '09 at 00:51

[Flags]
public enum DaysOfWeek
{
  Mon = 1,
  Tue = 2,
  Wed = 4,
  Thur = 8,
  Fri = 16,
  Sat = 32,
  Sun = 64
}

You have to specify the numbers, and increment them like this because it is storing the values in a bitwise fashion.

Then just define your method to take this enum

public void DoSomething(DaysOfWeek day)
{
  ...
}

and to call it do something like

DoSomething(DaysOfWeek.Mon | DaysOfWeek.Tue) // Both Monday and Tuesday

To check if one of the enum values was included check them using bitwise operations like

public void DoSomething(DaysOfWeek day)
{
  if ((day & DaysOfWeek.Mon) == DaysOfWeek.Mon) // Does a bitwise and then compares it to Mondays enum value
  {
    // Monday was passed in
  }
}

Doesn't answer the question. "In my particular situation, I would like to use the System.DayOfWeek" — Robert Paulson, Jun 23 '09 at 01:22
But it' exactly what I have been looking for. So thanks anyway. — Tillito, Mar 23 '11 at 21:28

score 5 · Answer 6 · edited Apr 29 '21 at 16:31

5

[Flags]
public enum DaysOfWeek{
    Sunday = 1 << 0,
    Monday = 1 << 1,
    Tuesday = 1 << 2,
    Wednesday = 1 << 3,
    Thursday = 1 << 4,
    Friday = 1 << 5,
    Saturday = 1 << 6
}

Call the method in this format

MethodName(DaysOfWeek.Tuesday | DaysOfWeek.Thursday);

Implement a EnumToArray method to get the options passed

private static void AddEntryToList(DaysOfWeek days, DaysOfWeek match, List<string> dayList, string entryText) {
    if ((days& match) != 0) {
        dayList.Add(entryText);
    }
}

internal static string[] EnumToArray(DaysOfWeek days) {
    List<string> verbList = new List<string>();

    AddEntryToList(days, HttpVerbs.Sunday, dayList, "Sunday");
    AddEntryToList(days, HttpVerbs.Monday , dayList, "Monday ");
    ...

    return dayList.ToArray();
}

edited Apr 29 '21 at 16:31

Alex Logvin

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answered Jun 23 '09 at 00:51

Rony

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Doesn't answer the question. "In my particular situation, I would like to use the System.DayOfWeek" – Robert Paulson Jun 23 '09 at 01:21
Thanks, Robert, but you really don't have to point this out on every answer. – Ronnie Overby Jun 23 '09 at 01:36
@Ronnie - Hardly my fault that there are so many near-duplicate answers that didn't actually answer the question. – Robert Paulson Jun 23 '09 at 02:01
@Rony - the enums ToString() and Enum.Parse() will correctly output / parse a [Flags] enumeration (as long as you're careful of enumeration versioning of course) – Robert Paulson Jun 23 '09 at 02:16
@Robert - I don't think anyone is blaming you. Just let the votes do the talking. – Ronnie Overby Jun 23 '09 at 12:22

score 5 · Answer 7 · answered Jun 23 '09 at 00:52

Mark your enum with the [Flags] attribute. Also ensure that all of your values are mutually exclusive (two values can't add up to equal another) like 1,2,4,8,16,32,64 in your case

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

When you have a method that accepts a DayOfWeek enum use the bitwise or operator (|) to use multiple members together. For example:

MyMethod(DayOfWeek.Sunday|DayOfWeek.Tuesday|DayOfWeek.Friday)

To check if the parameter contains a specific member, use the bitwise and operator (&) with the member you are checking for.

if(arg & DayOfWeek.Sunday == DayOfWeek.Sunday)
Console.WriteLine("Contains Sunday");

Doesn't answer the question. "In my particular situation, I would like to use the System.DayOfWeek" — Robert Paulson, Jun 23 '09 at 01:22

score 3 · Answer 8 · answered Jun 23 '09 at 00:58

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.

score 1 · Answer 9 · edited May 23 '17 at 10:31

1

With the help of the posted answers and these:

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

I feel like I understand it pretty well.

Thanks.

edited May 23 '17 at 10:31

Community

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answered Jun 23 '09 at 01:41

Ronnie Overby

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score -5 · Answer 10 · answered Jun 23 '09 at 00:45

-5

Something of this nature should show what you are looking for:

[Flags]
public enum SomeName
{
    Name1,
    Name2
}

public class SomeClass()
{
    public void SomeMethod(SomeName enumInput)
    {
        ...
    }
}

answered Jun 23 '09 at 00:45

Andrew Siemer

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How do you pass multiple enum values in C#?

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