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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