Sharing Add-in between Office Apps

Question

I have written an Office shared Add-in with C# and .NET 2.0. It uses the same COM Shim for all office apps. Currently, every instance creates its own instance of my class -- they have no knowledge of the fact that the add-in is running on another application.

Is it possible to make it so that, say, when the Word add-in launches it can detect that the Excel add-in is already running? Can they communicate between each other?

Let's say my dll is called Addin.dll. When, for example, Word opens, it runs the code in Addin.dll that implements the IExtensibility interface, and creates a class, let's call it WordAddin. When Excel opens, it also runs the code in Addin.dll, and it creates an instance of ExcelAddin. Now, suppose that Word is running and WordAddin exists. When Excel is opened, Addin.dll is loaded into a different AppDomain. It has no knowledge that WordAddin exists. I want ExcelAddin to have know WordAddin exists, and be able to communicate with it, perhaps through a parent class that creates both.

Anyone know how to do this?

Answer 1

You could do this using a Microsoft Message Queue (MSMQ): Use Microsoft Message Queuing in C# for inter-process communication

This code project article shows how to detect a running instance and how to copy command line parameters between them:

Single-Instance C# Application - for .NET 2.0

Not quite what you are asking but might be of interest: Detecting a running instance of a program and passing it information

Answer 2

I have in fact done exactly what you're asking about. I went for old fashioned windows messages. Nothing fancy - so it will just work! :-)

Let your addin create a "window" using the NativeWindow class and give it a predetermned, unique name. Then search for another instance of such a window using GetWindow and GetWindowText when your addin launches. Communicate using SendMessage or PostMessage. Easy as that.

Answer 3

That's very interesting Dan, but that sounds like a pretty big hack (not that there's anything wrong with that). What were some of the other options you considered? Ideally, I'd like to have one instance of a master class that is initialized when the first add-in loads and have that master class contain a list of the addin classes.

Answer 4

I ended up using named pipes to communicate between processes