Bitmask'ed Int到Enum []或Int []？ C＃

Question

I have an enum that looks like this:

enum foo{
a=0,
b=1,
c=2,
d=4
}

Building the flag / bitmask is fine, but is it possible to do something like

int i = 3;
var bar =  Enum.Split(foo,i);

Resulting in something like

bar = foo[]{a, b,c};

Thanks.

Answer 1

Try the following

public static IEnumerable<T> Split<T>(int value) {
  foreach (object cur in Enum.GetValues(typeof(T))) {
    var number = (int)(object)(T)cur;
    if (0 != (number & value)) {
      yield return (T)cur;
    }
  }
}

With this you can now write

int i = 3;
IEnumerable<foo> e = Split<foo>(i);

Note: This only works on enum values which derive from int (the default setting). It's also not entirely type safe as T can't be constrained to only enum values (nothing to do about that though)

Answer 2

You can use the FlagsAttribute on the enum and get lots of the functionality for free (no need to work at the bit level).

MSDN describes the attribute as:

Indicates that an enumeration can be treated as a bit field; that is, a set of flags.

Answer 3

The [FlagsAttribute] allows you to extract all of the valid values.

http://msdn.microsoft.com/en-us/library/system.flagsattribute.aspx

Answer 4

Try this:

TEnum[] EnumSplit<TEnum>(int mask)
{
    List<TEnum> values = new List<TEnum>();
    foreach(int enumValue in Enum.GetValues(typeof(TEnum)))
    {
        if(mask & enumValue == enumValue)
            values.Add((TEnum)enumValue);
    }
    return values.ToArray();
}

Call it like this:

var bar = EnumSplit<foo>(i);

Preferably, you want to change it to return IEnumerable<TEnum> instead of TEnum[] .

Answer 5

You could do this with a method which pulls the values from the Enum you pass:

public static T[] EnumSplit<T>(int value) where T : struct
{
    // Simplified as Enum.GetValues will complain if T is not an enum
    // However, you should add a check to make sure T implements FlagAttribute
    return (from vv in Enum.GetValues(typeof(T))
            where ((int)vv & value) != 0
            select (T)vv).ToArray();;
}

Answer 6

    var flags = Enum.GetValues(typeof (/* YourEnumType */))
                  .Cast</* YourEnumType */>()
                  .Select(v => enumValue.HasFlag(v))
                  .ToArray();