C# Enumeration 使用)

Emumeration 這個概念早在C時代就有了， 不過以前沒怎麼用過。

基本表達， 改變預設值和預設類型

Enumeration的預設值是從0開始的int如下： 
enum Direction
{
   UP,
   RIGHT
   DOWN,
   LEFT,
};
此時UP=0, DOWN=1...依此類推

改變預設值：
enum Direction
{
   UP=1,
   RIGHT=2,
   DOWN=3,
   LEFT=4,
};

改變類型（只能改變成：byte, sbyte, short, ushort, int, uint, long, ulong）：
enum Direction : long
{
    UP = 1111111111,
    DOWN = 1111111112,
    LEFT = 1111111113,
    RIGHT = 1111111114
};

訪問Enumeration變數的值

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

Enumeration變數的文字描述

如果想要Enumeration返回一點有意義的string，從而使用者能知道分別代表什麼， 則按如下定義：
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
};

使用如下方法來獲得文字描述：
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();
}

或者可以自己定義Discription Attributes:(來自：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;
    }
}