学步园

Emumeration 这个概念早在C时代就有了， 不过以前没怎么用过。

基本表达， 改变默认值和默认类型

Enumeration的默认值是从0开始的int如下： 
enum Direction
{
   UP,
   RIGHT
   DOWN,
   LEFT,
};
此时UP=0, DOWN=1...依此类推

改变默认值：
enum Direction
{
   UP=1,
   RIGHT=2,
   DOWN=3,
   LEFT=4,
};

改变类型（只能改变成：byte, sbyte, short, ushort, int, uint, long, ulong）：
enum Direction : long
{
    UP = 1111111111,
    DOWN = 1111111112,
    LEFT = 1111111113,
    RIGHT = 1111111114
};

访问Enumeration变量的值

赋值前先cast：
long direct = (long)Direction.UP;

Enumeration变量的文字描述

如果想要Enumeration返回一点有意义的string，从而用户能知道分别代表什么， 则按如下定义：
using System.ComponentModel;
enum Direction
{
    [Description("this means facing to UP (Negtive Y)")]
    UP = 1,
    [Description("this means facing to RIGHT (Positive X)")]
    RIGHT = 2,
    [Description("this means facing to DOWN (Positive Y)")]
    DOWN = 3,
    [Description("this means facing to LEFT (Negtive X)")]
    LEFT = 4
};

使用如下方法来获得文字描述：
using System.Reflection;
using System.ComponentModel;
public static String GetEnumDesc(Enum e)
{
    FieldInfo EnumInfo = e.GetType().GetField(e.ToString());
    DescriptionAttribute[] EnumAttributes = (DescriptionAttribute[]) EnumInfo.
        GetCustomAttributes (typeof(DescriptionAttribute), false);
    if (EnumAttributes.Length > 0)
    {
        return EnumAttributes[0].Description;
    }
    return e.ToString();
}

或者可以自己定义Discription Attributes:(来自：James Geurts' Blog)
enum Direction
{
    [EnumDescription("Rover is facing to UP (Negtive Y)")]
    UP = 1,
    [EnumDescription("Rover is facing to DOWN (Positive Y)")]
    DOWN = 2,
    [EnumDescription("Rover is facing to RIGHT (Positive X)")]
    RIGHT = 3,
    [EnumDescription("Rover is facing to LEFT (Negtive X)")]
    LEFT = 4
}; AttributeUsage(AttributeTargets.Field)]
public class EnumDescriptionAttribute : Attribute
{
    private string _text = "";
    public string Text
    {
        get { return this._text; }
    }
    public EnumDescriptionAttribute(string text)
    {
        _text = text;
    }
}