AOP的簡單示例

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Runtime.Remoting;
using System.Runtime.Remoting.Contexts;
using System.Runtime.Remoting.Proxies;
using System.Runtime.Remoting.Messaging;
using System.Runtime.Remoting.Services;
using System.Runtime.Remoting.Activation;


namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }


        private void button1_Click(object sender, EventArgs e)
        {
            BusinessHandler handler = new BusinessHandler();
            handler.DoSomething();
        }
    }
}


//業務層的類和方法，讓它繼承自上下文繫結類的基類
[MyInterceptor]
public class BusinessHandler : ContextBoundObject
{
    [MyInterceptorMethod]
    public void DoSomething()
    {
        MessageBox.Show("執行了方法本身！");
    }
}


//貼在方法上的標籤
[AttributeUsage(AttributeTargets.Method, AllowMultiple = false)]
public sealed class MyInterceptorMethodAttribute : Attribute { }


//貼在類上的標籤
[AttributeUsage(AttributeTargets.Class, AllowMultiple = false)]
public sealed class MyInterceptorAttribute : ContextAttribute, IContributeObjectSink
{
    public MyInterceptorAttribute()
        : base("MyInterceptor")
    { }


    //實現IContributeObjectSink介面當中的訊息接收器介面
    public IMessageSink GetObjectSink(MarshalByRefObject obj, IMessageSink next)
    {
        return new MyAopHandler(next);
    }
}


//AOP方法處理類，實現了IMessageSink介面，以便返回給IContributeObjectSink介面的GetObjectSink方法
public sealed class MyAopHandler : IMessageSink
{
    //下一個接收器
    private IMessageSink nextSink;
    public IMessageSink NextSink
    {
        get { return nextSink; }
    }
    public MyAopHandler(IMessageSink nextSink)
    {
        this.nextSink = nextSink;
    }


    //同步處理方法
    public IMessage SyncProcessMessage(IMessage msg)
    {
        IMessage retMsg = null;
        
        //方法呼叫訊息介面
        IMethodCallMessage call = msg as IMethodCallMessage;


        //如果被呼叫的方法沒打MyInterceptorMethodAttribute標籤
        if (call == null || (Attribute.GetCustomAttribute(call.MethodBase, typeof(MyInterceptorMethodAttribute))) == null)
        {
            retMsg = nextSink.SyncProcessMessage(msg);
        }
        //如果打了MyInterceptorMethodAttribute標籤
        else
        {
            MessageBox.Show("執行之前");
            retMsg = nextSink.SyncProcessMessage(msg);
            MessageBox.Show("執行之後");
        }


        return retMsg;
    }


    //非同步處理方法（不需要）
    public IMessageCtrl AsyncProcessMessage(IMessage msg, IMessageSink replySink)
    {
        return null;
    }
}