如何进行定义特性（Attribute），并且在程序中如何检索定义的特性，可以根据用户定义的不同特性进行不同的操作。

using System;
using System.Collections;
using System.Runtime.InteropServices;
using System.Diagnostics;
using System.Reflection;

namespace Test
{
public class Myclass
{
public static void Main()
{
HelpAttribute HelpAttr;

string assemblyName;
Process p = Process.GetCurrentProcess();
assemblyName = p.ProcessName + ".exe";
Assembly a = Assembly.LoadFrom(assemblyName);

Type b = a.GetType("Test.Class1");
foreach (Attribute attr in b.GetCustomAttributes(true))
{
HelpAttr = attr as HelpAttribute;
if (null != HelpAttr)
{
Console.WriteLine("Description of {0}:/n{1},Version={2}",
assemblyName,HelpAttr.Description,HelpAttr.Version);
}
}

Type c = a.GetType("Test.Class2");

foreach (Attribute attr in c.GetCustomAttributes(true))
{
HelpAttr = attr as HelpAttribute;
if (null != HelpAttr)
{
Console.WriteLine("Description of {0}:/n{1},Version={2}",
assemblyName,HelpAttr.Description,HelpAttr.Version);
}
}

Type d = a.GetType("Test.Class3");

foreach (Attribute attr in d.GetCustomAttributes(true))
{
HelpAttr = attr as HelpAttribute;
if (null != HelpAttr)
{
Console.WriteLine("Description of {0}:/n{1},Version={2}",
assemblyName,HelpAttr.Description,HelpAttr.Version);
}
}
}
}

[Help("This is Class1")]
public class Class1
{
}

[Help("This is Class2", Version = "1.0")]
public class Class2
{
}

[Help("This is Class3", Version = "2.0",
Description = "This is do-nothing class")]
public class Class3
{
}

[AttributeUsage(AttributeTargets.Class, AllowMultiple = true,
Inherited = true)]
public class HelpAttribute : Attribute
{
public HelpAttribute(String Description_in)
{
this.description = Description_in;
this.version = "No Version is defined for this class";
}

protected string description;
public string Description
{
get
{
return this.description;
}
set
{
this.description = value;
}
}

protected string version;
public string Version
{
get
{
return this.version;
}
set
{
this.version = value;
}
}
}
}

结果为：
Description of ConsoleApplication7.exe:
This is Class1,Version=No Version is defined for this class
Description of ConsoleApplication7.exe:
This is Class2,Version=1.0
Description of ConsoleApplication7.exe:
This is do-nothing class,Version=2.0