AOP入门

一 AOP

Aspect-Oriented Programming（面向方面编程，AOP），如果我们基于面向对象的思想开发软件，一切皆是对象，而对于对象内部则无能为力。AOP利用一种称为“横切”的技术，剖解开封装的对象内部，并将那些影响了多个类的行为封装到一个可重用模块，并将其名为“Aspect”，即方面。所谓 “方面”，简单地说，就是将那些与业务无关，却为业务模块所共同调用的逻辑或责任，例如事务处理、日志管理、权限控制等，封装起来，便于减少系统的重复代码，降低模块间的耦合度，并有利于未来的可操作性和可维护性。

二 AOP framework

http://sourceforge.net/projects/aopnet/

http://www.postsharp.org/

http://www.aspectc.org/

三基于postsharp的实例

1）参考：http://www.sharpcrafters.com/postsharp/documentation/getting-started

2）QuickTraceAttribute.cs

using System;
using System.Collections.Generic;
using System.Text;
using PostSharp.Aspects;

namespace Trace
{
    [Serializable]
    public sealed class QuickTraceAttribute : OnMethodBoundaryAspect
    {
        private string enteringMessage, leavingMessage;

        public override void CompileTimeInitialize(System.Reflection.MethodBase method, AspectInfo aspectInfo)
        {
            string methodName = method.DeclaringType.FullName + "." + method.Name;
            this.enteringMessage = "Entering " + methodName;
            this.leavingMessage = "Leaving " + methodName;
        }

        public override void OnEntry(MethodExecutionArgs args)
        {
            System.Diagnostics.Trace.WriteLine( this.enteringMessage);
            System.Diagnostics.Trace.Indent();
        }

        public override void OnExit(MethodExecutionArgs args)
        {
            System.Diagnostics.Trace.Unindent();
            System.Diagnostics.Trace.WriteLine( this.leavingMessage );
        }

        public override void OnException(MethodExecutionArgs args)
        {
            System.Diagnostics.Trace.Unindent();
            System.Diagnostics.Trace.WriteLine(this.leavingMessage + " with exception: " +
                args.Exception.Message + Environment.NewLine + args.Exception.ToString());
        }
    }
}

3）Program.cs

using System;
using System.Collections.Generic;
using System.Text;
using System.Threading;

// apply quick trace attribute to all methods from 'mscorlib' and 'system.threading.*'
[assembly: Trace.QuickTrace(AttributeTargetAssemblies = "mscorlib", AttributeTargetTypes = "System.Threading.*")]

namespace Trace
{
    class Program
    {
        static void Main(string[] args)
        {
            System.Diagnostics.Trace.Listeners.Add( new System.Diagnostics.TextWriterTraceListener( Console.Out ) );

            Method1();
        }

        [QuickTrace]
        static void Method1()
        {
            Method2();
        }

        [QuickTrace]
        static void Method2()
        {
            Method3();
        }

        [QuickTrace]
        static void Method3()
        {
            Thread.Sleep( 10 );
        }
    }
}

4）结果