How to enumerate an enum?

Wednesday, May 23, 2012

How to enumerate an enum?

How can you enumerate a enum in C#?

e.g. the following does not compile:




public enum Suit

{

        Spades,

        Hearts,

        Clubs,

        Diamonds

}



public void EnumerateAllSuitsDemoMethod()

{

        foreach (Suit suit in Suit)

        {

                DoSomething(suit);

        }

}

It gives the compile time error: 'Suit' is a 'type' but is used like a 'variable'

It fails on the Suit keyword, the 2nd one.

Edit: Got rid of Console.WriteLine(), it was confusing people

Source: Tips4all

12 comments:

UserMay 23, 2012 at 3:28 AM
foreach (Suit suit in Enum.GetValues(typeof(Suit)))
{
}
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UserMay 23, 2012 at 3:28 AM
It looks to me like you really want to print out the names of each enum, rather than the values. In which case Enum.GetNames seems to be the right approach.

public enum Suits
{
Spades,
Hearts,
Clubs,
Diamonds,
NumSuits
}

public void PrintAllSuits()
{
foreach(string name in Enum.GetNames(typeof(Suits)))
{
System.Console.WriteLine(suit);
}
}

By the way, incrementing the value is not a good way to enumerate the values of an enum. You should do this instead.

I would use Enum.GetValues(typeof(Suit)) instead.

public enum Suits
{
Spades,
Hearts,
Clubs,
Diamonds,
NumSuits
}

public void PrintAllSuits()
{
foreach(var suit in Enum.GetValues(typeof(Suits)))
{
System.Console.WriteLine(suit.ToString());
}
}
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UserMay 23, 2012 at 3:28 AM
I made some extensions for easy enum usage, maybe someone can use it...

public static class EnumExtensions
{
/// <summary>
/// Gets all items for an enum value.
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="value">The value.</param>
/// <returns></returns>
public static IEnumerable<T> GetAllItems<T>(this Enum value)
{
foreach (object item in Enum.GetValues(typeof(T)))
{
yield return (T)item;
}
}

/// <summary>
/// Gets all items for an enum type.
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="value">The value.</param>
/// <returns></returns>
public static IEnumerable<T> GetAllItems<T>() where T : struct
{
foreach (object item in Enum.GetValues(typeof(T)))
{
yield return (T)item;
}
}

/// <summary>
/// Gets all combined items from an enum value.
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="value">The value.</param>
/// <returns></returns>
/// <example>
/// Displays ValueA and ValueB.
/// <code>
/// EnumExample dummy = EnumExample.Combi;
/// foreach (var item in dummy.GetAllSelectedItems<EnumExample>())
/// {
/// Console.WriteLine(item);
/// }
/// </code>
/// </example>
public static IEnumerable<T> GetAllSelectedItems<T>(this Enum value)
{
int valueAsInt = Convert.ToInt32(value, CultureInfo.InvariantCulture);

foreach (object item in Enum.GetValues(typeof(T)))
{
int itemAsInt = Convert.ToInt32(item, CultureInfo.InvariantCulture);

if (itemAsInt == (valueAsInt & itemAsInt))
{
yield return (T)item;
}
}
}

/// <summary>
/// Determines whether the enum value contains a specific value.
/// </summary>
/// <param name="value">The value.</param>
/// <param name="request">The request.</param>
/// <returns>
/// <c>true</c> if value contains the specified value; otherwise, <c>false</c>.
/// </returns>
/// <example>
/// <code>
/// EnumExample dummy = EnumExample.Combi;
/// if (dummy.Contains<EnumExample>(EnumExample.ValueA))
/// {
/// Console.WriteLine("dummy contains EnumExample.ValueA");
/// }
/// </code>
/// </example>
public static bool Contains<T>(this Enum value, T request)
{
int valueAsInt = Convert.ToInt32(value, CultureInfo.InvariantCulture);
int requestAsInt = Convert.ToInt32(request, CultureInfo.InvariantCulture);

if (requestAsInt == (valueAsInt & requestAsInt))
{
return true;
}

return false;
}
}

The enum itself must be decorated with the FlagsAttribute

[Flags]
public enum EnumExample
{
ValueA = 1,
ValueB = 2,
ValueC = 4,
ValueD = 8,
Combi = ValueA | ValueB
}
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UserMay 23, 2012 at 3:28 AM
The .NET compact framework does not support Enum.GetValues. Here's a good workaround from Ideas 2.0: Enum.GetValues in Compact Framework:

public IEnumerable<Enum> GetValues(Enum enumeration)
{
List<Enum> enumerations = new List<Enum>();
foreach (FieldInfo fieldInfo in enumeration.GetType().GetFields(
BindingFlags.Static | BindingFlags.Public))
{
enumerations.Add((Enum)fieldInfo.GetValue(enumeration));
}
return enumerations;
}
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UserMay 23, 2012 at 3:28 AM
I think this is more efficient than other suggestions because GetValues() is not called each time you have a loop. It is also more concise. And you get a compile-time error not a runtime exception if Suit is not an enum.

EnumLoop<Suit>.ForEach((suit) => {
DoSomethingWith(suit);
});

EnumLoop has this completely generic definition:

class EnumLoop<Key> where Key : struct, IConvertible {
static readonly Key[] arr = (Key[])Enum.GetValues(typeof(Key));
static internal void ForEach(Action<Key> act) {
for (int i = 0; i < arr.Length; i++) {
act(arr[i]);
}
}
}
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UserMay 23, 2012 at 3:28 AM
You wont' get Enmu.GetValues() in Silverlight.

-- Original Blog Post by Einar Ingebrigtsen --

public class EnumHelper
{
public static T[] GetValues<T>()
{
Type enumType = typeof(T);

if (!enumType.IsEnum)
{
throw new ArgumentException("Type '" + enumType.Name + "' is not an enum");
}

List<T> values = new List<T>();

var fields = from field in enumType.GetFields()
where field.IsLiteral
select field;

foreach (FieldInfo field in fields)
{
object value = field.GetValue(enumType);
values.Add((T)value);
}

return values.ToArray();
}

public static object[] GetValues(Type enumType)
{
if (!enumType.IsEnum)
{
throw new ArgumentException("Type '" + enumType.Name + "' is not an enum");
}

List<object> values = new List<object>();

var fields = from field in enumType.GetFields()
where field.IsLiteral
select field;

foreach (FieldInfo field in fields)
{
object value = field.GetValue(enumType);
values.Add(value);
}

return values.ToArray();
}
}
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UserMay 23, 2012 at 3:28 AM
public void PrintAllSuits()
{
foreach(string suit in Enum.GetNames(typeof(Suits)))
{
Console.WriteLine(suit);
}
}
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Replies
UserMay 23, 2012 at 3:28 AM
Just to add my solution, which works in compact framework (3.5) and supports Type checking at compile time:

public static List<T> getEnumValues<T>() where T : new() {
T valueType = new T();
return typeof(T).GetFields()
.Select(fieldInfo => (T)fieldInfo.GetValue(valueType))
.Distinct()
.ToList();
}

public static List<String> getEnumNames<T>() {
return typeof (T).GetFields()
.Select(info => info.Name)
.Distinct()
.ToList();
}

- If anyone knows how to get rid of the "T valueType = new T()", I'd be happy to see a solution.

A call would look like this:

List<MyEnum> result = Utils.getEnumValues<MyEnum>();
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UserMay 23, 2012 at 3:28 AM
it works with

foreach (string _name in Enum.GetNames(typeof(Suits)) { ... }
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UserMay 23, 2012 at 3:28 AM
I think you can use

Enum.GetNames(Suit)
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UserMay 23, 2012 at 3:28 AM
> foreach (Suit suit in Enum.GetValues(typeof(Suit))) { }

I've heard vague rumours that this is
terifically slow. Anyone know? – Orion
Edwards Oct 15 '08 at 1:31 7

I think caching the array would speed it up considerably. It looks like you're getting a new array (through reflection) every time. Rather:

Array ar = Enum.GetValues(typeof(Suit));
foreach(Suit temp_suit in ar) Do_Something(temp_suit);

That's at least a little faster, ja?
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UserMay 23, 2012 at 3:28 AM
You can enumerate enum by Values and By names.
Here are more details about that.
Click Here
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Wednesday, May 23, 2012

How to enumerate an enum?

12 comments:

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