C# 的AOP实现

闲来无事，做了一个AOP示例，此示例只能捕获方法调用事件，无法动态阻止方法调用的执行。因为取消后构造返回值成了难题，返回null貌似会报错。如果不需要这个功能，其实还是很完美的。

缺点是没有以接口方式实现，使用类必须继承ContextBoundObject。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Runtime.Remoting.Proxies;
using System.Runtime.Remoting.Contexts;
using System.Runtime.Remoting.Activation;
using System.Runtime.Remoting.Messaging;

namespace Csharp实现AOP方法拦截
{
#region AOP Helper

public class MyApoAspect : IMessageSink
{
private IMessageSink _NextSink = null;
private IMyAopMethodFilter _MethodFilter;

internal MyApoAspect(IMessageSink msgSink, IMyAopMethodFilter methodFilter)
{
_NextSink = msgSink;
_MethodFilter = methodFilter;
}

public IMessageCtrl AsyncProcessMessage(IMessage msg, IMessageSink replySink)
{
IMessage message = this.SyncProcessMessage(msg);
replySink.SyncProcessMessage(message);
return null;

}

public IMessageSink  NextSink
{
get { return _NextSink; }
}

public IMessage SyncProcessMessage(IMessage msg)
{
var cancel = false;
_MethodFilter.PreAopMethodFilter(msg,ref cancel);
if (cancel)
{
//此处不知如何返回
return null;
}
IMessage returnMethod = _NextSink.SyncProcessMessage(msg);
_MethodFilter.PostAopMethodFilter(msg);
return returnMethod;
}
}

public class MyAopProperty: IContextProperty, IContributeObjectSink
{
private IMyAopMethodFilter _MethodFilter;

public MyAopProperty(IMyAopMethodFilter methodFilter)
{
_MethodFilter = methodFilter;
}

public void  Freeze(Context newContext) { }

public bool  IsNewContextOK(Context newCtx)
{
return true;
}

public string  Name
{
get
{
return "MyAopProperty";
}
}

public IMessageSink  GetObjectSink(MarshalByRefObject obj, IMessageSink nextSink)
{
return new MyApoAspect(nextSink, _MethodFilter);
}
}

[AttributeUsage(AttributeTargets.Class)]
public class MyAopAttribute : ContextAttribute, IMyAopMethodFilter
{
private IMyAopMethodFilter _MethodFilter;

public MyAopAttribute()
: base("MyAopAttribute")
{
_MethodFilter = this;
}

public override void GetPropertiesForNewContext(IConstructionCallMessage ccm)
{
ccm.ContextProperties.Add(new MyAopProperty(_MethodFilter));
}

protected virtual void OnPreAopMethodFilter(IMessage msg, ref bool Cancel)
{
throw new NotImplementedException();
}

protected virtual void OnPostAopMethodFilter(IMessage msg)
{
throw new NotImplementedException();
}

public void PreAopMethodFilter(IMessage msg ,ref bool Cancel)
{
this.OnPreAopMethodFilter(msg,ref Cancel);
}

public void PostAopMethodFilter(IMessage msg)
{
this.OnPostAopMethodFilter(msg);
}
}

public interface IMyAopMethodFilter
{
void PreAopMethodFilter(IMessage msg, ref bool Cancel);
void PostAopMethodFilter(IMessage msg);
}

#endregion

#region AOP Demo

public class Class1AopAttribute : MyAopAttribute
{
protected override void OnPreAopMethodFilter(IMessage msg, ref bool Cancel)
{
IMethodMessage call = msg as IMethodMessage;
Type type = Type.GetType(call.TypeName);
string callStr = type.Name + "." + call.MethodName;
var args = call.Args;
Console.WriteLine("在执行前拦截到" + callStr);
}

protected override void OnPostAopMethodFilter(IMessage msg)
{
IMethodMessage call = msg as IMethodMessage;
Type type = Type.GetType(call.TypeName);
string callStr = type.Name + "." + call.MethodName;
var args = call.Args;
Console.WriteLine("在执行后拦截到" + callStr);
}
}

[Class1AopAttribute()]
public class Class1:ContextBoundObject
{
public int A { get; set; }

public int B(ref int p)
{
p++;
return p + 1;
}
}

class Program
{
static void Main(string[] args)
{
Class1 c1 = new Class1();
c1.A = 2;

int p = 0;
c1.B(ref p);

Console.ReadLine();
}
}

#endregion
}