Event Interception with Castle DynamicProxy

Question

Hi,

In googling I can't seem to find an example of intercepting event on a proxied type and it doesn't seem to be working for me. Is there a way I can do this (ie. use an IInterceptor when an event is invoked)?

Thanks.

Answer 1

I doubt it. Castle Dynamic Proxy works by intercepting the calls made on the proxy. Events are not made on the proxy. They're callbacks handled by the .NET framework.

Answer 2

I ended up using the ComponentCreated event, then adding a dynamic event handler with a DynamicMethod to accomplish what I wanted:

private static readonly MethodInfo internalPublishEventMethod =
    typeof(EventPublisher).GetMethod("PublishEvent", BindingFlags.Static | BindingFlags.NonPublic);

private void Container_ComponentCreated(global::Castle.Core.ComponentModel model, object instance)
{
    if (instance != null)
    {
        Type type = instance.GetType();

        var eventPublisherAttribute = type.GetAttribute<EventPublisherAttribute>();

        if (eventPublisherAttribute != null)
        {
            foreach (EventInfo ei in type.GetEvents())
            {
                if (eventPublisherAttribute.PublishAllEvents || ei.GetCustomAttributes(typeof(PublishedEventAttribute), false).Length > 0)
                {
                    // emit an event handler

                    MethodInfo invoke = ei.EventHandlerType.GetMethod("Invoke");
                    Type[] parameters = invoke.GetParameters().Select(p => p.ParameterType).ToArray();

                    var method = new DynamicMethod(string.Empty, null, parameters, instance.GetType(),
                                                   true);
                    ILGenerator generator = method.GetILGenerator();
                    // sender
                    generator.Emit(OpCodes.Ldarg_0);
                    // args
                    generator.Emit(OpCodes.Ldarg_1);
                    // topic
                    generator.Emit(OpCodes.Ldstr, ei.Name);
                    generator.Emit(OpCodes.Call, internalPublishEventMethod);
                    generator.Emit(OpCodes.Ret);

                    Delegate d = method.CreateDelegate(ei.EventHandlerType);
                    ei.AddEventHandler(instance, d);
                }
            }
        }
    }
}

private static void PublishEvent(object sender, EventArgs e, string topic)
{
    if (e != null)
    {
    // do stuff
    }
}