FlagsAttribute是为了什么？

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

我做了

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可以组合枚举的值.如果没有此属性,组合这些值将导致未知值(但它仍然有效).使用该属性,可以正确解释组合

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()