Listen for events in another application

Question

Suppose I have two applications written in C#. The first is a third party application that raises an event called "OnEmailSent".

The second is a custom app that I've written that I would like to somehow subscribe to the "OnEmailSent" even of the first application.

Is there any way that I could somehow attach the second application to an instance of the first application to listen for "OnEmailSent" event?

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So for further clarification, my specific scenario is that we have a custom third party application written in c# that raises an "OnEmailSent" event. We can see the event exists using reflector.

What we want to do is have some other actions take place when this component sends an email.

The most efficient way we can think of would be to be able to use some form of IPC as anders has suggested and listen for the OnEmailSent event being raised by the third party component.

Because the component is written in C# we are toying with the idea of writing another C# application that can attach itself to the executing process and when it detect the OnEmailSent event has been raise it will execute it's own event handling code.

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I might be missing something, but from what I understand of how remoting works is that there would need to be a server defining some sort of contract that the client can subscribe to.

I was more thinking about a scenario where someone has written a standalone application like outlook for example, that exposes events that I would like to subscribe to from another application.

I guess the scenario I'm thinking of is the .net debugger and how it can attach to executing assemblies to inspect the code whilst it's running.

Answer 1

In order for two applications (separate processes) to exchange events, they must agree on how these events are communicated. There are many different ways of doing this, and exactly which method to use may depend on architecture and context. The general term for this kind of information exchange between processes is Inter-process Communication (IPC). There exists many standard ways of doing IPC, the most common being files, pipes, (network) sockets, remote procedure calls (RPC) and shared memory. On Windows it's also common to use window messages.

I am not sure how this works for .NET/C# applications on Windows, but in native Win32 applications you can hook on to the message loop of external processes and "spy" on the messages they are sending. If your program generates a message event when the desired function is called, this could be a way to detect it.

If you are implementing both applications yourself you can chose to use any IPC method you prefer. Network sockets and higher-level socket-based protocols like HTTP, XML-RPC and SOAP are very popular these days, as they allow you do run the applications on different physical machines as well (given that they are connected via a network).