C# 标志问题

Question

我有一个枚举(标志)

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

我想将两个标志分配给一个变量，如下所示:

var displayFlags = DisplayMode.Parse | DisplayMode.Inverted;

但是，当我调试并在分配后立即将鼠标悬停在该变量上时，它说 displayFlags is DisplayMode.Dim | DisplayMode.Inverted.

我缺少/不理解什么？

Answer 1

您错过了为标志分配合理的值，例如:

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

这样每个值在数字表示中都有一个单独的位。

如果您不相信自己将值加倍的能力，可以使用位移:

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

来自 FlagsAttribute 的文档:

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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