C# Enumeration 使用

1、關於enum的定義

enum Fabric{Cotton = 1,Silk = 2,Wool = 4,Rayon = 8,Other = 128}

2、符號名和常數值的互相轉換              Fabric fab = Fabric.Cotton;
            int fabNum = (int)fab;//轉換為常數值。必須使用強制轉換。            Fabric fabString = (Fabric)1;//常數值轉換成符號名。如果使用ToString()，則是（（Fabric）1）.ToString()，注意必須有括弧。             string fabType = fab.ToString();//顯示符號名
            string fabVal = fab.ToString ("D");//顯示常數值  3、獲得所有符號名的方法（具體參見Enum類）          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、將枚舉作為位標誌來處理

根據下面的兩個例子，粗略地說，一方面，設定標誌[Flags]或者[FlagsAttribute]，則表明要將符號名列舉出來；另一方面，可以通過強制轉換，將數字轉換為 符號名。說不準確。看下面的例子體會吧。注意：

          例一：          Fabric fab = Fabric.Cotton | Fabric.Rayon | Fabric.Silk;
          Console.WriteLine("MyFabric = {0}", fab);//輸出：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、枚舉作為函數參數。經常和switch結合起來使用。下面舉例

        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、上面三點一個完整的例子

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

        //將枚舉作為參數傳遞
        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類的使用

Enum.IsDefinde、Enum.Parse兩種方法經常一起使用，來確定一個值或符號是否是一個枚舉的成員，然後建立一個執行個體。Enum.GetName列印出一個成員的值；Enum.GetNames列印出所有成員的值。其中注意typeof的使用。這一點很重要。

        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;
    }
}