Enum.HasFlag is not working as expected

Question

I have a Enum with Flags like this:

[Flags]
public enum ItemType
{
    Shop,
    Farm,
    Weapon,
    Process,
    Sale
}

Then I have several objects in a list with some flags set and some flags not set. It looks like this:

public static List<ItemInfo> AllItems = new List<ItemInfo>
{
        new ItemInfo{ID = 1, ItemType = ItemType.Shop, Name = "Wasserflasche", usable = true, Thirst = 50, Hunger = 0, Weight = 0.50m, SalesPrice = 2.50m, PurchasePrice = 5,  ItemUseAnimation = new Animation("Trinken", "amb@world_human_drinking@coffee@female@idle_a", "idle_a", (AnimationFlags.OnlyAnimateUpperBody | AnimationFlags.AllowPlayerControl)) },
        new ItemInfo{ID = 2, ItemType = ItemType.Sale, Name = "Sandwich", usable = true, Thirst = 0, Hunger = 50, Weight = 0.5m, PurchasePrice = 10, SalesPrice = 5, ItemUseAnimation = new Animation("Essen", "mp_player_inteat@pnq", "intro", 0) },
        new ItemInfo{ID = 3, ItemType = (ItemType.Shop|ItemType.Process), Name = "Apfel", FarmType = FarmTypes.Apfel, usable = true, Thirst = 25, Hunger = 25, Weight = 0.5m, PurchasePrice = 5, SalesPrice = 2, ItemFarmAnimation = new Animation("Apfel", "amb@prop_human_movie_bulb@base","base", AnimationFlags.Loop)},
        new ItemInfo{ID = 4, ItemType = ItemType.Process, Name = "Brötchen", usable = true, Thirst = -10, Hunger = 40, Weight = 0.5m, PurchasePrice = 7.50m, SalesPrice = 4}
}

Then I go trough the list with a loop and ask if the flag ItemType.Shop is set or not, like this:

List<ItemInfo> allShopItems = ItemInfo.AllItems.ToList();
foreach(ItemInfo i in allShopItems)
{
    if (i.ItemType.HasFlag(ItemType.Shop))
    {
        API.consoleOutput(i.Name);
    }
}

This is the output of my loop - it shows all items in the list, and the .HasFlag method always returns true in this case.

Wasserflasche
Sandwich
Apfel
Brötchen

Flags need the values to be powers of 2, e.g. `1, 2, 4, 8, 16`. The *only* thing the `Flags` attribute does is change how the enum is serialized to a string. — , Mar 19 '18 at 15:13
You have revealed a syntax highlighting bug with your Brötchen *G* — ViRuSTriNiTy, Mar 19 '18 at 15:16
You have a funny enum, where something can be a `Shop` and a `Weapon` and a `Sale` all at the same time. `ItemType` may not be the best name for it, or else you don't really want an enum. — Jeroen Mostert, Mar 19 '18 at 15:19
@JeroenMostert the item can be used in diferrent locations,like a normal shop, weaponshop, saleshouse, and so on — Dennis Larisch, Mar 19 '18 at 15:21

score 7 · Accepted Answer · edited Mar 19 '18 at 15:32

7

Try to assign values to your enum

[Flags]
public enum ItemType 
{
    Shop = 1,
    Farm = 2,
    Weapon = 4,
    Process = 8,
    Sale = 16
}

Here are some Guidelines for FlagsAttribute and Enum (excerpt from Microsoft Docs)

Use the FlagsAttribute custom attribute for an enumeration only if a bitwise operation (AND, OR, EXCLUSIVE OR) is to be performed on a numeric value.
Define enumeration constants in powers of two, that is, 1, 2, 4, 8, and so on. This means the individual flags in combined enumeration constants do not overlap.

edited Mar 19 '18 at 15:32

Black Frog

11,595
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answered Mar 19 '18 at 15:14

CodeReaper

775
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2

You should not use `0` as a flag enum. Also, you have duplicate `2` values. – ps2goat Mar 19 '18 at 15:15
3

Having a Flags enum with anything other than `None` as an option equal to `0` is almost always a bad plan. – Damien_The_Unbeliever Mar 19 '18 at 15:15
Consider changing the `Shop = 0` for `None = 0` – Cleptus Mar 19 '18 at 15:16
thanks for the tips. On this page: https://msdn.microsoft.com/en-us/library/system.flagsattribute(v=vs.110).aspx Section:"Guidelines for FlagsAttribute and Enum" provides additional best practises. – CodeReaper Mar 19 '18 at 15:20
why using 0 as a value is bad idea ? – IronHide Dec 28 '18 at 14:34

score 4 · Answer 2 · edited Mar 19 '18 at 15:31

4

You should assign values to your enums. All the flags attribute does is change how the ToString method works. I would use a bitwise operator to make it less likely to make a mistake:

[Flags]
public enum ItemType
{
    Shop = 1 << 0, // == 1
    Farm = 1 << 1, // == 2
    Weapon = 1 << 2, // == 4
    Process = 1 << 3, // == 8
    Sale = 1 << 4 // == 16
}

edited Mar 19 '18 at 15:31

Henrik

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answered Mar 19 '18 at 15:25

nelsontruran

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Enum.HasFlag is not working as expected

2 Answers2