Question

我要做的是能够拦截对象的方法和属性的调用，以解决交叉问题。我正在使用基于代理的AOP ContextBoundObject。

然而，这不适用于递归方法调用，对目标的第一次调用将被代理拦截并成功调用，允许我在此处进行交叉切换。但是，第一种方法中的后续方法调用将保留在目标类中，并且代理不会截获，就像没有编组一样！

有什么方法可以让它发挥作用吗？（我试图避免像PostSharp，Unity或Spring.Net这样的第三方库）

class Program
{
    static void Main(string[] args)
    {
        var t = new SimpleObject();
        t.TestMethod1();
    }
}


[Intercept]
class SimpleObject : ContextBoundObject
{
    public string TestMethod1()
    {
        return TestMethod2();
    }

    public string TestMethod2()
    {
        return "test";
    }
}

[AttributeUsage(AttributeTargets.Class)]
public class InterceptAttribute : ContextAttribute, IContributeObjectSink
{
    public InterceptAttribute()
        : base("Intercept")
    { }

    public override bool IsContextOK(Context ctx, IConstructionCallMessage ctorMsg)
    {
        return false;
    }

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


public class InterceptSink : IMessageSink
{
    public IMessageSink NextSink { get; private set; }

    public InterceptSink(IMessageSink nextSink)
    {
        this.NextSink = nextSink;
    }

    public IMessage SyncProcessMessage(IMessage msg)
    {
        IMethodCallMessage mcm = (msg as IMethodCallMessage);

        // { cross-cut here }

        IMessage rtnMsg = this.NextSink.SyncProcessMessage(msg);
        IMethodReturnMessage mrm = (rtnMsg as IMethodReturnMessage);

        // { cross-cut here }

        return mrm;
    }

    public IMessageCtrl AsyncProcessMessage(IMessage msg, IMessageSink replySink)
    {
        return null;
    }
}

Answer 1

C＃设计师从未赞成过AOP，没有简单的方法来拦截方法调用而不使用Proxies和Marshaling，它们有各自的缺点！如果有人想拦截方法/属性调用（例如交叉问题），我发现RealProxy可以提供一些帮助。

RealProxy来自MSDN：

在任何类型的远程边界中使用对象的客户端是实际上为对象使用透明代理。透明的代理提供了实际对象所在的错觉客户的空间。它通过将对其发出的呼叫转发给它来实现这一点使用远程基础设施的真实对象。

注意：使用RealProxy代理的类型必须是接口或从MarshalByRefObject继承。

以下是使用Factory方法在运行时创建对象代理的RealProxy的一些实现：

public abstract class RuntimeProxy
{
    public static readonly object Default = new object();

    public static Target Create<Target>(Target instance, RuntimeProxyInterceptor interceptor) where Target : class
    {
        return (Target)new InternalProxy<Target>(instance, interceptor).GetTransparentProxy();
    }

    public static Target Create<Target>(Target instance, Func<RuntimeProxyInvoker, object> factory) where Target : class
    {
        return (Target)new InternalProxy<Target>(instance, new InternalRuntimeProxyInterceptor(factory)).GetTransparentProxy();
    }


    class InternalProxy<Target> : RealProxy where Target : class
    {
        readonly object Instance;
        readonly RuntimeProxyInterceptor Interceptor;

        public InternalProxy(Target instance, RuntimeProxyInterceptor interceptor)
            : base(typeof(Target))
        {
            Instance = instance;
            Interceptor = interceptor;
        }

        public override IMessage Invoke(IMessage msg)
        {
            var methodCall = (IMethodCallMessage)msg;
            var method = (MethodInfo)methodCall.MethodBase;

            try
            {
                var result = Interceptor.Invoke(new InternalRuntimeProxyInterceptorInvoker(Instance, method, methodCall.InArgs));

                if (result == RuntimeProxy.Default)
                    result = method.ReturnType.IsPrimitive ? Activator.CreateInstance(method.ReturnType) : null;

                return new ReturnMessage(result, null, 0, methodCall.LogicalCallContext, methodCall);
            }
            catch (Exception ex)
            {
                if (ex is TargetInvocationException && ex.InnerException != null)
                    return new ReturnMessage(ex.InnerException, msg as IMethodCallMessage);

                return new ReturnMessage(ex, msg as IMethodCallMessage);
            }
        }
    }

    class InternalRuntimeProxyInterceptor : RuntimeProxyInterceptor
    {
        readonly Func<RuntimeProxyInvoker, object> Factory;

        public InternalRuntimeProxyInterceptor(Func<RuntimeProxyInvoker, object> factory)
        {
            this.Factory = factory;
        }

        public override object Invoke(RuntimeProxyInvoker invoker)
        {
            return Factory(invoker);
        }
    }

    class InternalRuntimeProxyInterceptorInvoker : RuntimeProxyInvoker
    {
        public InternalRuntimeProxyInterceptorInvoker(object target, MethodInfo method, object[] args)
            : base(target, method, args)
        { }
    }
}

public abstract class RuntimeProxyInterceptor
{
    public virtual object Invoke(RuntimeProxyInvoker invoker)
    {
        return invoker.Invoke();
    }
}

public abstract class RuntimeProxyInvoker
{
    public readonly object Target;
    public readonly MethodInfo Method;
    public readonly ReadOnlyCollection<object> Arguments;

    public RuntimeProxyInvoker(object target, MethodInfo method, object[] args)
    {
        this.Target = target;
        this.Method = method;
        this.Arguments = new ReadOnlyCollection<object>(args);
    }

    public object Invoke()
    {
        return Invoke(this.Target);
    }

    public object Invoke(object target)
    {
        if (target == null)
            throw new ArgumentNullException("target");

        try
        {
            return this.Method.Invoke(target, this.Arguments.ToArray());
        }
        catch (TargetInvocationException ex)
        {
            throw ex.InnerException;
        }
    }
}

您可以使用RuntimeProxy作为工厂来创建对象的代理并拦截所有方法/属性调用并调用实际方法。

以下是一个示例：

class SomeClass : MarshalByRefObject
{
    public int Mul(int a, int b)
    {
        return a * b;
    }

    public void SetValue(int val)
    {
        this.Val = val;
    }

    public int Val { get; set; }
}

使用RuntimeProxy类为SomeClass类的实例创建代理并拦截调用：

var test = new SomeClass();
var proxy = RuntimeProxy.Create(test, t =>
{
    // cross-cut here

    return t.Invoke();          // invoke the actual call
});

var res = proxy.Mul(3, 4);      // method with return value
proxy.SetValue(2);              // void method, setting some property
var val = proxy.Val;            // property access

如果您不想从MarshalByRefObject类继承，可以使用接口类型。

使用Proxies在C＃中调用拦截方法

1 个答案: