正确使用Enum的FlagsAttribute

正确使用Enum的FlagsAttribute

FlagsAttribute 标志枚举对象的值可以包括多个枚举成员，每个成员代表枚举值中的一个位域

使用步骤

1. 添加标记[Flags]
2. 用 2 的幂（即 1、2、4、8 等）定义枚举常量,比如0,1,1<<1,1<<2,1<<3
3. 标记[Flags]的枚举项之间可以进行NOT,OR,AND,XOR操作

例子1

[Flags]
public enum DaysOfWeek
{
    Sunday = 1,
    Monday = 1 << 1,
    Tuesday = 1 << 2,
    Wednesday = 1 << 3,
    Thursday = 1 << 4,
    Friday = 1 << 5,
    Saturday = 1 << 6,
}
 var workDays1 = DaysOfWeek.Monday | DaysOfWeek.Tuesday |
 DaysOfWeek.Thursday | DaysOfWeek.Thursday | DaysOfWeek.Friday;

 var workDays2 = DaysOfWeek.Friday | DaysOfWeek.Saturday 
| DaysOfWeek.Sunday;

 ~workDays1 
//DaysOfWeek.Saturday,DaysOfWeek.Sunday

 workDays1 ^workDays2 
//DaysOfWeek.Monday, DaysOfWeek.Tuesday,DaysOfWeek.Thursday,
//DaysOfWeek.Thursday,DaysOfWeek.Saturday, DaysOfWeek.Sunday

 workDays1&DaysOfWeek.Monday //DaysOfWeek.Monday

例子2

//判断是否包含某项

 //.net4.0新增
 if (workDays1.HasFlag(DaysOfWeek.Monday))
 {
     //...
 }

 //4.0以前的版本
 if ((workDays1 & DaysOfWeek.Monday) == DaysOfWeek.Monday)
 {
     //...
 }