Question

I am currently in deep need of logging for an existing application, and can’t afford to add the level of logging I expect directly into the code. As a workaround, I’d be happy to have a certain amount of logging done each time an event is fired.

I am considering a solution where I could, at runtime, parse the whole application to wrap all event-to-handler bindings with event-to-wrapper-to-handler; and, ideally, unwrap them at runtime too. In Pseudo-code, this would be:

IDictionary<Event, Action<object, EventArgs>) originalBindings = ...;

public void SetWrapBindings()
{
   var allBindingsToReplace = Assembly.GetAssembly().GETALLEVENTS()
      .Where(eventInfo => eventInfo.GetOtherMethods().Any());

   foreach(var binding in allBindingsToReplace)
   {
     binding.event -= binding.handler;
     binding.event += HandlerWrapper;
     originalBindings.Add(binding.event, binding.handler);
   }

}

public static void HandlerWrapper(object o, EventArgs e)
{
    // Do some logging
    try
    {
       var handler = originalBindings.TryGetValue(/* something */);
       handler.Invoke(o, e);
    }
    // Do more logging
}

In this bunch of pseudo-code there are lots of steps I was not able to write, possibly because I didn’t find the correct API use, but maybe also because some operation in that is theoretically impossible (in which case I’d love to know why). These are:

• Iterating over all events of the application (this would probably be easy)
• Identifying a good key for my IDictionary
• At each step, get the relevant information from the context

Of course, binding one extra handler to each existing event (pre/post-executing a routine without really wrapping the handler) would help, but executing the real handler inside a try-catch is a big nice to have.

Any partial answer is still greatly appreciated

Answer 1

If you’re looking for non-invasive system-wide logging, you’d be better off using an aspect-oriented programming framework like PostSharp. This page provides a decent jumping off point for what you’re looking for.

Edit: To add to this, look at implementing an EventInterceptionAspect if you really do just want to know when any event is raised. Again, the PostSharp blog is a good source of info, and this article shows an implementation of this aspect that does simple stdout logging of adding, removing, and invoking.