枚举类型位标致[Flags]特性的使用以及为枚举类型添加方法

假设有段代码是这样的，需要判断角色装备哪些武器，然后根据角色的这个属性来进行其它的一些操作。这时候我们可以用枚举来标记角色可以装备的武器。

   public enum Equipment
    {
        刀,
        枪,
        箭,
        弓
    }

    public sealed class Player
    {
        internal Equipment equipmentState;//用于描述角色可以使用哪些武器
       //......其它成员
    }

这就有个问题了，当角色可以装备多种武器的时候，难道要用多个变量去表示他可以使用的武器吗？又或者是在Equipment类型中加入新的成员，刀和箭，刀和箭和弓...... 造成这种原因的是Player中的equipmentState只能表示一种状态，不能表示多种状态。

即它的值只能是刀,枪,箭,弓中的一个。

这时候可以用Flags特性为修饰Equipment类型。它可以让equipmentState有能力可以表示成多种状态，现在equipmentState就相当于集合一样。

namespace UsageOfFlagsAttribute
{
    [Flags]
    public enum Equipment
    {
        NONE = 0x0000,
        刀 = 0x0001,
        枪 = 0x0002,
        箭 = 0x0004,
        弓 = 0x0008
    }

    public sealed class Player
    {
        internal Equipment equipmentState;//用于描述角色可以使用哪些武器
    }


    class Program
    {
        static void Main(string[] args)
        {
            Player player = new Player();
            player.equipmentState = Equipment.刀 | Equipment.弓;  //可以表示成多种状态的集合
        }
    }
}

用Flags标记后也就可以按位计算了，一般枚举有3种按位计算。

按位或（“|”）：将指定的符号加入到枚举实例中

按位与（”&“）：判断枚举实例中是否有指定的符号  

异或（”^“）：删除枚举实例中指定的符号

  class Program
    {
        static void Main(string[] args)
        {
            Player player = new Player();

            //按位或
            player.equipmentState = Equipment.刀;
            player.equipmentState = player.equipmentState | Equipment.弓;
            Console.WriteLine(player.equipmentState.ToString());//打印结果：刀,弓

            //按位与
            player.equipmentState = Equipment.刀 | Equipment.弓;
            player.equipmentState = player.equipmentState & Equipment.刀;
            Console.WriteLine(player.equipmentState.ToString());  //打印结果 ： 刀

            //异或
            player.equipmentState = Equipment.刀 | Equipment.弓;
            player.equipmentState = player.equipmentState ^ Equipment.弓;
            Console.WriteLine(player.equipmentState.ToString());  //打印结果 ： 刀

            Console.ReadKey();
        }
    }

但是每次都要写  player.equipmentState = player.equipmentState ^ Equipment.弓;  这么赋值代码的可读性不好，而且容易浪费时间。因此可以扩展方法来封装这些操作。

 public static class EnumExtendMethods
    {
        /// <summary>
        /// 判断位标致的枚举实例中是否有指定符号
        /// </summary>
        /// <param name="eqipment">实例</param>
        /// <param name="checkState">指定的符号</param>
        /// <returns></returns>
        public static bool Contains(this Equipment equipment,Equipment checkState)
        {
            if (checkState == 0)
            {
                throw new ArgumentOutOfRangeException("checkState", "不能为NONE");
            }
            return (equipment & checkState) == checkState;
        }

        /// <summary>
        /// 将指定的符号从枚举实例中移除
        /// </summary>
        /// <param name="equipment"></param>
        /// <param name="removeState">指定要移除的符号</param>
        /// <returns></returns>
        public static Equipment Remove(this Equipment equipment, Equipment removeState)
        {
            return equipment ^ removeState;
        }

        /// <summary>
        /// 向枚举实例中加入指定的符号
        /// </summary>
        /// <param name="equipment"></param>
        /// <param name="addState"></param>
        /// <returns></returns>
        public static Equipment Append(this Equipment equipment, Equipment addState)
        {
            return equipment | addState;
        }
    }

现在可以这样调用了

    class Program
    {
        static void Main(string[] args)
        {
            Player player = new Player();

            //按位或
            player.equipmentState = Equipment.刀;
            player.equipmentState = player.equipmentState.Append(Equipment.弓);
            Console.WriteLine(player.equipmentState.ToString());//打印结果：刀,弓

            //按位与
            player.equipmentState = Equipment.刀 | Equipment.弓;
            if (player.equipmentState.Contains(Equipment.刀))
            {
                Console.WriteLine(player.equipmentState.ToString());  //打印结果 ： 刀,弓
            }

            //异或
            player.equipmentState = Equipment.刀 | Equipment.弓;
            player.equipmentState = player.equipmentState.Remove(Equipment.弓);
            Console.WriteLine(player.equipmentState.ToString());  //打印结果 ： 刀

            Console.ReadKey();
        }
    }