C#扩展方法,用于检查枚举是否设置了标志

Question

我想创建一个扩展方法来检查枚举是否有一个标志.

DaysOfWeek workDays = DaysOfWeek.Monday | DaysOfWeek.Tuesday | DaysOfWeek.Wednesday;
// instead of this:
if ((workDays & DaysOfWeek.Monday) == DaysOfWeek.Monday)
   ...

// I want this:
if (workDays.ContainsFlag(DaysOfWeek.Monday))
   ...

我怎么能做到这一点？(如果有一个类已经完成了这个,那么我会很感激如何解释这个问题;我已经把这个方法弄得太久了!)

提前致谢

Answer 1

.NET 4已经包含了这个功能,如果可能的话,升级.

days.HasFlag(DaysOfWeek.Monday);

如果无法升级,这里是所述方法的实现:

public bool HasFlag(Enum flag)
{
    if (!this.GetType().IsEquivalentTo(flag.GetType())) {
        throw new ArgumentException(Environment.GetResourceString("Argument_EnumTypeDoesNotMatch", flag.GetType(), this.GetType())); 
    }

    ulong uFlag = ToUInt64(flag.GetValue()); 
    ulong uThis = ToUInt64(GetValue());
    return ((uThis & uFlag) == uFlag); 
}

您可以轻松构建等效的扩展方法:

public static bool HasFlag(this Enum @this, Enum flag)
{
    // as above, but with '@this' substituted for 'this'
}