Attributes in C#

拮取自(This article is modified from) https://secure.codeproject.com/KB/cs/attributes.aspx?display=Print

using System;
using System.Reflection;
using System.Diagnostics;

class A
{
    [AttributeUsage(AttributeTargets.All, AllowMultiple = true, Inherited = false)]
    
    //attaching Help attribute to entire assembly
    [assembly: Help("This Assembly demonstrates custom attributes creation and their run-time query.")]
    //our custom attribute class
    public class HelpAttribute : Attribute
    {
        public HelpAttribute(String Description_in)
        {
            this.description = Description_in;
        }
        protected String description;
        public String Description
        {
            get
            {
                return this.description;
            }
        }
    }
    //attaching Help attribute to our AnyClass
    [Help("This is a do-nothing Class.")]
    [Help("This is a do-nothing Class2")]
    public class AnyClass
    {
        //attaching Help attribute to our AnyMethod

        [Help("This is a do-nothing Method.")]
        public void AnyMethod() {}
        //attaching Help attribute to our AnyInt Field
        [Help("This is any Integer.")]
        public int AnyInt;
    }

    class QueryApp
    {
        public static void Main()
        {

            Type type = typeof(AnyClass);
            HelpAttribute HelpAttr;

            //Querying Class Attributes
            foreach (Attribute attr in type.GetCustomAttributes(true))
            {
                HelpAttr = attr as HelpAttribute;
                if (null != HelpAttr)
                    Console.WriteLine("Description of AnyClass:\n{0}", HelpAttr.Description);
            }

            //Querying Class-Method Attributes  
            foreach (MethodInfo method in type.GetMethods())
            {
                foreach (Attribute attr in method.GetCustomAttributes(true))
                {
                    HelpAttr = attr as HelpAttribute;
                    if (null != HelpAttr)
                        Console.WriteLine("Description of {0}:\n{1}",method.Name, HelpAttr.Description);
                }
            }
            
            //Querying Class-Field (only public) Attributes
            foreach (FieldInfo field in type.GetFields())
            {
                foreach (Attribute attr in field.GetCustomAttributes(true))
                {
                    HelpAttr = attr as HelpAttribute;
                    if (null != HelpAttr)
                        Console.WriteLine("Description of {0}:\n{1}", field.Name, HelpAttr.Description);
                }
            }
        }
    }
}

 

印出結果：

Description of AnyClass:
This is a do-nothing Class2
Description of AnyClass:
This is a do-nothing Class.
Description of AnyMethod:
This is a do-nothing Method.
Description of AnyInt:
This is any Integer.