How to check which enum values are set based on a combined value

Question

I am having 5 checkboxes.

public enum animals : int
{
    Cat      = 1
    ,Dog     = 2
    ,Mouse   = 3
    ,Rat     = 4
    ,Lizzard = 5
}

On saving my window I can sum up they checkboxes that are checked, in int res_flags and save it.

int res_flags = 0;

if ((bool)this.chbCat.IsChecked)        res_flags |= (int)animals.Cat;
if ((bool)this.chbDog.IsChecked)        res_flags |= (int)animals.Dog;
if ((bool)this.chbMouse.IsChecked)      res_flags |= (int)animals.Mouse;
if ((bool)this.chbRat.IsChecked)        res_flags |= (int)animals.Rat;
if ((bool)this.chbLizzard.IsChecked)    res_flags |= (int)animals.Lizzard;

How can I check at the start which were checked based on the int res_flags?

Answer 1

How can I check at the start which were checked based on the int res_flags?

In this case it is very convenient to add the [Flags] attribute to the enum, and make the values powers of 2. It's easy to make sure the values are powers of 2 by using bit-shift operator<< with an increasing value.

Then you can use Enum.HasFlag to check if a specific flag is set:

[Flags]
public enum animals : int
{
    Cat = 1 << 0,
    Dog = 1 << 1,
    Mouse = 1 << 2,
    Rat = 1 << 3,
    Lizzard = 1 << 4
}

static void Main(string[] args)
{
    animals res_flags = animals.Cat | animals.Dog;

    Console.WriteLine(res_flags.HasFlag(animals.Cat));
    Console.WriteLine(res_flags.HasFlag(animals.Dog));
    Console.WriteLine(res_flags.HasFlag(animals.Mouse));
    Console.WriteLine(res_flags.HasFlag(animals.Rat));
    Console.WriteLine(res_flags.HasFlag(animals.Lizzard));
}

Output:

True
True
False
False
False

Live demo

Note that res_flags is no longer of type int, but rather of the enum type animals.