C# problem with flags

Question

I have an enum (flag)

[Flags]
public enum DisplayMode
{
    None,
    Dim,
    Inverted,
    Parse,
    Italics,
    Bold
}

I want to assign two of the flags to a variable, like this:

var displayFlags = DisplayMode.Parse | DisplayMode.Inverted;

However, when I debug and hover over this variable immediately after it is assigned, it says displayFlags is DisplayMode.Dim | DisplayMode.Inverted.

What am I missing/not understanding?

Answer 1

You've missed assigning the flags sensible values, e.g.:

[Flags]
public enum DisplayMode
{
    None = 0,
    Dim = 1,
    Inverted = 2,
    Parse = 4,
    Italics = 8,
    Bold = 16
}

That way each value has a separate bit in the numeric representation.

If you don't trust your ability to double values, you can use bit shifting:

[Flags]
public enum DisplayMode
{
    None = 0,
    Dim =      1 << 0,
    Inverted = 1 << 1,
    Parse =    1 << 2,
    Italics =  1 << 3,
    Bold =     1 << 4
}

From the documentation from FlagsAttribute:

Guidelines for FlagsAttribute and Enum

• 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.

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