特性

很好的例子，一看就懂

 

//Copyright (C) Microsoft Corporation.  All rights reserved.

// AttributesTutorial.cs
// This example shows the use of class and method attributes.

using System;
using System.Reflection;
using System.Collections;

// The IsTested class is a user-defined custom attribute class.
// It can be applied to any declaration including
//  - types (struct, class, enum, delegate)
//  - members (methods, fields, events, properties, indexers)
// It is used with no arguments.
public class IsTestedAttribute : Attribute
{
    public override string ToString()
    {
        return "Is Tested";
    }
}

// The AuthorAttribute class is a user-defined attribute class.
// It can be applied to classes and struct declarations only.
// It takes one unnamed string argument (the author's name).
// It has one optional named argument Version, which is of type int.
[AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct)]
public class AuthorAttribute : Attribute
{
    // This constructor specifies the unnamed arguments to the attribute class.
    public AuthorAttribute(string name)
    {
        this.name = name;
        this.version = 0;
    }

    // This property is readonly (it has no set accessor)
    // so it cannot be used as a named argument to this attribute.
    public string Name 
    {
        get 
        {
            return name;
        }
    }

    // This property is read-write (it has a set accessor)
    // so it can be used as a named argument when using this
    // class as an attribute class.
    public int Version
    {
        get 
        {
            return version;
        }
        set 
        {
            version = value;
        }
    }

    public override string ToString()
    {
        string value = "Author : " + Name;
        if (version != 0)
        {
            value += " Version : " + Version.ToString();
        }
        return value;
    }

    private string name;
    private int version;
}

// Here you attach the AuthorAttribute user-defined custom attribute to 
// the Account class. The unnamed string argument is passed to the 
// AuthorAttribute class's constructor when creating the attributes.
[Author("Joe Programmer")]
class Account
{
    // Attach the IsTestedAttribute custom attribute to this method.
    [IsTested]
    public void AddOrder(Order orderToAdd)
    {
        orders.Add(orderToAdd);
    }

    private ArrayList orders = new ArrayList();
}

// Attach the AuthorAttribute and IsTestedAttribute custom attributes 
// to this class.
// Note the use of the 'Version' named argument to the AuthorAttribute.
[Author("Jane Programmer", Version = 2), IsTested()]
class Order
{
    // add stuff here ...
}

class MainClass
{
   private static bool IsMemberTested(MemberInfo member)
   {
        foreach (object attribute in member.GetCustomAttributes(true))
        {
            if (attribute is IsTestedAttribute)
            {
               return true;
            }
        }
      return false;
   }

    private static void DumpAttributes(MemberInfo member)
    {
        Console.WriteLine("Attributes for : " + member.Name);
        foreach (object attribute in member.GetCustomAttributes(true))
        {
            Console.WriteLine(attribute);
        }
    }

    public static void Main()
    {
        // display attributes for Account class
        DumpAttributes(typeof(Account));

        // display list of tested members
        foreach (MethodInfo method in (typeof(Account)).GetMethods())
        {
            if (IsMemberTested(method))
            {
               Console.WriteLine("Member {0} is tested!", method.Name);
            }
            else
            {
               Console.WriteLine("Member {0} is NOT tested!", method.Name);
            }
        }
        Console.WriteLine();

        // display attributes for Order class
        DumpAttributes(typeof(Order));

        // display attributes for methods on the Order class
        foreach (MethodInfo method in (typeof(Order)).GetMethods())
        {
           if (IsMemberTested(method))
           {
               Console.WriteLine("Member {0} is tested!", method.Name);
           }
           else
           {
               Console.WriteLine("Member {0} is NOT tested!", method.Name);
           }
        }
        Console.WriteLine();
    }
}