看看通用扩展方法，如果枚举包含一个标志 [英] Generic extension method to see if an enum contains a flag

问题描述

考虑到这一点：

[Flags]
public enum MyEnum {
    One = 1,
    Two = 2,
    Four = 4,
    Eight = 8
}

public static class FlagsHelper
{
    public static bool Contains(this MyEnum keys, MyEnum flag)
    {
        return (keys & flag) != 0;
    }
}

是否有可能包含了写一个通用版本将适用于任何枚举而不仅仅是 MyEnum ？

Is it possible to write a generic version of Contains that would work for any enum and not just MyEnum?

修改

这将是我的版本阅读你的答案后：

This would be my version after reading your answers:

    public static bool Contains(this Enum keys, Enum flag)
    {
        ulong keysVal = Convert.ToUInt64(keys);
        ulong flagVal = Convert.ToUInt64(flag);

        return (keysVal & flagVal) == flagVal;
    }

刚刚意识到是一个坏主意来检查我检查的方式（收益率（键和放大器;标志）！= 0; ），因为标志参数可能是实际上的几个标志和常识要做的事情就是返回true，只有当键包含了所有的人。另外，我也不会检查空值，甚至以确保它们是同一类型。我可能的希望的使用不同类型。

Just realized is a bad idea to check the way I was checking (return (keys & flag) != 0;), because the flag parameter might be actually several flags and the common sense thing to do is return true only if keys contains all of them. Also, I wouldn't check for null values or even make sure they are the same type. I might want to use different types.

推荐答案

我根据这个方法一串，这样的&安培;谷歌搜索，以及通过使用反射器，看看有什么MS所做的.NET 4 HasFlags方法。

I based this method off of a bunch of SO & Google searches, and a by using reflector to see what MS did for the .NET 4 HasFlags method.

public static class EnumExt
{
    /// <summary>
    /// Check to see if a flags enumeration has a specific flag set.
    /// </summary>
    /// <param name="variable">Flags enumeration to check</param>
    /// <param name="value">Flag to check for</param>
    /// <returns></returns>
    public static bool HasFlag(this Enum variable, Enum value)
    {
        if (variable == null)
            return false;

        if (value == null)
            throw new ArgumentNullException("value");

        // Not as good as the .NET 4 version of this function, but should be good enough
        if (!Enum.IsDefined(variable.GetType(), value))
        {
            throw new ArgumentException(string.Format(
                "Enumeration type mismatch.  The flag is of type '{0}', was expecting '{1}'.",
                value.GetType(), variable.GetType()));
        }

        ulong num = Convert.ToUInt64(value);
        return ((Convert.ToUInt64(variable) & num) == num);

    }

}

注：

Notes:

• 此处理空值


• 请问类型检查


• 转换为ULONG，并且可以处理任何积极的枚举值。 微软提醒反对使用负标志枚举反正：
  • This handles nulls
  • Does type checking
  • Converts to a ulong, and can handle any positive enum value. Microsoft cautions against the use of negative flags enumerations anyway:

    如果你定义一个负数的枚举常量，因为许多标记位置可能被设置为1的标志，这可能使你的代码混乱和鼓励编码错误要小心。

  
  

  Use caution if you define a negative number as a flag enumerated constant because many flag positions might be set to 1, which might make your code confusing and encourage coding errors.

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