.net - FlagsAttribute 有什么用？

Question

下面的代码有什么区别

' no Flags'
Public Enum MyEnum
  Monday = 1
  Tuesday = 2
  Wednesday = 4
  Thursday = 8
End Enum

和

<Flags()> _ 
Public Enum MyEnum
  Monday = 1
  Tuesday = 2
  Wednesday = 4
  Thursday = 8
End Enum

我做

Dim days As MyEnum = MyEnum.Monday Or MyEnum.Tuesday Or MyEnum.Wednesday 

If (days And MyEnum.Tuesday) = MyEnum.Tuesday Then
  Console.WriteLine("Tuesday OK") ' here'
Else
  Console.WriteLine("Tuesday NOK")
End If

If (days And MyEnum.Thursday ) = MyEnum.Thursday Then
  Console.WriteLine("Thursday OK")
Else
  Console.WriteLine("Thursday NOK") ' here'
End If

并在两种情况下获得相同的结果(有或没有 FlagAttribute)。

Answer 1

基本上，它告诉 CLR 枚举的值可以组合。如果没有此属性，组合这些值将产生一个未知值(但它仍然有效)。有了属性，组合就被正确解释了

没有 Flags 属性:

' Gives "Monday, Tuesday" '
Dim s As String = (MyEnum.Monday Or MyEnum.Tuesday).ToString() 

没有 Flags 属性:

' Gives "3" '
Dim s As String = (MyEnum.Monday Or MyEnum.Tuesday).ToString()