Decoding a bitmask from a value in C#

Question

I am trying to decode a bitmask

[Flags]
public enum Amenities
{
    BusinessCenter = 1,
    FitnessCenter = 2,
    HotTub = 4,
    InternetAccess = 8,
    KidsActivities = 16,
    Kitchen = 32,
    PetsAllowed = 64,
    Pool = 128,
    Restaurant = 256,
    Spa = 512,
    Whirlpool = 1024,
    Breakfast = 2048,
    Babysitting = 4096,
    Jacuzzi = 8192,
    Parking = 16384,
    RoomService = 32768,
    AccessibleTravel = 65536,
    AccessibleBathroom = 131072,
    RollShower = 262144,
    HandicappedParking = 524288,
    InRoomAccessibility = 1048576,
    AccessibilityDeaf = 2097152,
    BrailleSignage = 4194304,
    FreeAirportShuttle = 8388608,
    IndoorPool =  16777216,
    OutdoorPool = 33554432,
    ExtendedParking = 67108864,
    FreeParking = 134217728
}

How do I write a function that decodes a value like 5722635 and returns a list of all Amenities that are encoded in 5722635.

the result should look like this:

This Property has the following Amenities:

• Business Center
• Fitness Center
• Internet Access
• Available Spa On-site
• Babysitting
• Parking
• Accessible Path of Travel
• Accessible Bathroom
• Roll-in Shower
• In-room Accessibility
• Braille or Raised Signage

I have been trying things like

public List<Amenities> Decode(long mask)
        {
            var list = new List<Amenities>();
            for (var index = 0; index < 16; index++)
            {
                var bit = 1 << index;
                if (0 != (bit & mask))
                {
                    list.Add(new Amenities(index));
                }
            }
            return list;
        }

But can not get it to work. Any suggestions on how to make this work properly would be appreciated.

Butyraldehyde

16 isn't enough and that new syntax to cast probably doesn't work – Colum

the new syntax definitely does not work. You cannot create a 'new' instance of an enum member like that – Heterolysis

Answer 1

What about one-liner?

var mask = (Amenities)5722635;

var result =
    Enum.GetValues(typeof(Amenities))
        .Cast<Amenities>()
        .Where(value => mask.HasFlag(value))
        .ToList();

You can cache result of Enum.GetValues(typeof(Amenities)).Cast<Amenities>() in order to improve performance.

Spireme

This simple solution did get the job done... thanx pwas – Butyraldehyde

Answer 2

Firstly, your method is taking in a long, yet your enum implicitly uses an int as the underlying data type. Either store the value as an int or change the underlying data type in your enum to a long: [Flags] public enum Amenities : long { ... }

Secondly, if your enum is marked with the FlagsAttribute you really don't need to turn the value into an list of values, you can use the Enum.HasFlag() method to check for a flagged value. You'll have to cast your long into an Amenities type first:

var amenities = (Amenities)mask;

if (amentities.HasFlag(Amenities.BusinessCenter)) { ... }

---

But, if you really want to split that flag into a list of amenities instead:

public IList<Amenities> Decode(long mask)
{
        var amenities = (Amenities)mask;
        var list = new List<Amenities>();

        foreach (Amenities amenity in Enum.GetValues(typeof(Amenities))
        {
            if (amenities.HasFlag(amenity))
                list.Add(amenity);
        }

        return list;
}

Rabies

This also works very well and follows the initial idea I was after. Thank you m-y – Butyraldehyde