C# Enumeration
/* from: http://blog.csdn.net/camel0564/archive/2008/07/31/2748420.aspx */

1、关于enum的定义
enum Fabric
{
Cotton = 1,
Silk = 2,
Wool = 4,
Rayon = 8,
Other = 128
}
2、符号名和常数值的互相转换
 
            Fabric fab = Fabric.Cotton;
            int fabNum = (int)fab;//转换为常数值。必须使用强制转换。
            Fabric fabString = (Fabric)1;//常数值转换成符号名。如果使用ToString()，则是（（Fabric）1）.ToString()，注意必须有括号。

            string fabType = fab.ToString();//显示符号名
            string fabVal = fab.ToString ("D");//显示常数值
 
3、获得所有符号名的方法（具体参见Enum类）
 
        public enum MyFamily
        {
            YANGZHIPING = 1,
            GUANGUIQIN = 2,
            YANGHAORAN = 4,
            LIWEI = 8,
            GUANGUIZHI = 16,
            LISIWEN = 32,
            LISIHUA = 64,
        }
 
            foreach (string s in Enum.GetNames(typeof(MyFamily)))
            {
                Console.WriteLine(s);
            }
 
4、将枚举作为位标志来处理
根据下面的两个例子，粗略地说，一方面，设置标志[Flags]或者[FlagsAttribute]，则表明要将符号名列举出来；另一方面，可以通过强制转换，将数字转换为符号名。说不准确。看下面的例子体会吧。注意：
          例一：
          Fabric fab = Fabric.Cotton | Fabric.Rayon | Fabric.Silk;
          Console.WriteLine("MyFabric = {0}", fab);//输出：Fabric.Cotton | Fabric.Rayon | Fabric.Silk;
例二：
class FlagsAttributeDemo
{
    // Define an Enum without FlagsAttribute.
    enum SingleHue : short
    {
        Black = 0,
        Red = 1,
        Green = 2,
        Blue = 4
    };

    // Define an Enum with FlagsAttribute.
    [FlagsAttribute]
    enum MultiHue : short
    {
        Black = 0,
        Red = 1,
        Green = 2,
        Blue = 4
    };

    static void Main( )
    {
        Console.WriteLine(
            "This example of the FlagsAttribute attribute \n" +
            "generates the following output." );
        Console.WriteLine(
            "\nAll possible combinations of values of an \n" +
            "Enum without FlagsAttribute:\n" );
       
        // Display all possible combinations of values.
        for( int val = 0; val <= 8; val++ )
            Console.WriteLine( "{0,3} - {1}",  val, ( (SingleHue)val ).ToString( ) );

        Console.WriteLine(  "\nAll possible combinations of values of an \n" + "Enum with FlagsAttribute:\n" );
       
        // Display all possible combinations of values.
        // Also display an invalid value.
        for( int val = 0; val <= 8; val++ )
            Console.WriteLine ( "{0,3} - {1}",  val, ( (MultiHue)val ).ToString( ) );
    }
}

/*
This example of the FlagsAttribute attribute
generates the following output.

All possible combinations of values of an
Enum without FlagsAttribute:

  0 - Black
  1 - Red
  2 - Green
  3 - 3
  4 - Blue
  5 - 5
  6 - 6
  7 - 7
  8 - 8

All possible combinations of values of an
Enum with FlagsAttribute:

  0 - Black
  1 - Red
  2 - Green
  3 - Red, Green
  4 - Blue
  5 - Red, Blue
  6 - Green, Blue
  7 - Red, Green, Blue
  8 - 8
*/
5、枚举作为函数参数。经常和switch结合起来使用。下面举例
        public static double GetPrice(Fabric fab)
        {
            switch (fab)
            {
                case Fabric.Cotton: return (3.55);
                case Fabric.Silk: return (5.65);
                case Fabric.Wool: return (4.05);
                case Fabric.Rayon: return (3.20);
                case Fabric.Other: return (2.50);
                default: return (0.0);
            }
        }

6、上面三点一个完整的例子

        //1、enum的定义
        public enum Fabric : short
        {
            Cotton = 1,
            Silk = 2,
            Wool = 3,
            Rayon = 8,
            Other = 128
        }

        //将枚举作为参数传递
        public static double GetPrice(Fabric fab)
        {
            switch (fab)
            {
                case Fabric.Cotton: return (3.55);
                case Fabric.Silk : return (5.65);
                case Fabric.Wool: return (4.05);
                case Fabric.Rayon: return (3.20);
                case Fabric.Other: return (2.50);
                default: return (0.0);
            }
        }

        public static void Main()
        {
            Fabric fab = Fabric.Cotton;
            int fabNum = (int)fab;
            string fabType = fab.ToString();
            string fabVal = fab.ToString ("D");
            double cost = GetPrice(fab);
            Console.WriteLine("fabNum = {0}\nfabType = {1}\nfabVal = {2}\n", fabNum, fabType, fabVal);
            Console.WriteLine("cost = {0}", cost);
        }

7、Enum类的使用

Enum.IsDefinde、Enum.Parse两种方法经常一起使用，来确定一个值或符号是否是一个枚举的成员，然后创建一个实例。Enum.GetName打印出一个成员的值；Enum.GetNames打印出所有成员的值。其中注意typeof的使用。这一点很重要。

        public enum MyFamily
        {
            YANGZHIPING = 1,
            GUANGUIQIN = 2,
            YANGHAORAN = 4,
            LIWEI = 8,
            GUANGUIZHI = 16,
            LISIWEN = 32,
            LISIHUA = 64,
        }

            string s = "YANGHAORAN";
            if (Enum.IsDefined(typeof(MyFamily), s))
            {
                MyFamily f = (MyFamily)Enum.Parse(typeof(MyFamily), s);
                GetMyFamily(f);
                Console.WriteLine("The name is:" + Enum. GetName(typeof(MyFamily), 2));
                string[] sa = Enum.GetNames(typeof(MyFamily));
                foreach (string ss in sa)
                {
                    Console.WriteLine(ss);

8. 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;
    }
}

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