How to call a VSTO AddIn method from a separate C# project?

Question

I have a C# Excel Add-in project "MyExcelAddIn" that has a public method Foo() to do something complex. For testing purposes, the add-in also defines a toolbar button which is wired to Foo() so I can test this and verify that clicking the button calls Foo() and does what I want it to do. This is fine.

Now I want to call this method from a C# Windows Forms project. In the Windows Forms project I can create an Excel instance and make it visible and verify that my VSTO add-in is running as I can see the button and it works. But I can't work out how to call Foo() programatically from the Windows Forms project. I've googled a bit and got as far as getting the "MyExcelAddIn" COMAddIn object, but can't work out how to call Foo().

It looks something like this:

// Create Excel and make it visible
Application excelApp = new Application();
excelApp.Visible = true;

// I know my VSTO add-in is running because I can see my test button
// Now get a reference to my VSTO add-in
Microsoft.Office.Core.COMAddIns comAddIns = _excelApp.COMAddIns;
object addinName = "MyExcelAddIn";
Microsoft.Office.Core.COMAddIn myAddin = comAddIns.Item(ref addinName);
// This works, but now what? How do I make a call on myAddin?
// Note that myAddin.Object is null...

So I want to know what I can do to call Foo() from my Windows Forms application. Note that I have full control over both the Windows Forms application and the add-in and I suspect I have to make changes to both of them (particularly the add-in) but I have no idea how to do this.

Note that this is a VS2008 C# application and I'm using Excel 2003.

score 5 · Answer 1 · answered May 14 '09 at 04:53

If you're building an application-level add-in, I believe this may be your answer: MSDN VSTO Article

It involves two steps: (From the article)

In your add-in, expose an object to other solutions.
In another solution, access the object exposed by your add-in, and call members of the object.

The other solution may be: (Again from the article)

Any solution that is running in a different process than your add-in (these types of solutions are also named out-of-process clients). These include applications that automate an Office application, such as a Windows Forms or console application, and add-ins that are loaded in a different process.

This should have been answer! – Dan Ling Nov 23 '10 at 14:14 — Dan Ling, Nov 23 '10 at 14:14

score 1 · Accepted Answer · answered Mar 14 '09 at 16:21

1

I'm using the SendMessage Win32 API to do this. My C# Add-in creates a "NativeWindow" with a uniqe window title that the WinForm app can locate.

answered Mar 14 '09 at 16:21

Dan Byström

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How to do this ? any tutorial? where can i get this SendMessage Win32 API ? – Sangram Nandkhile Sep 22 '11 at 07:47

score 0 · Answer 3 · answered Jul 01 '15 at 20:43

For anyone else who finds this here's what I did:

        object addInName = "AddinName";
        var excelApplication = (Microsoft.Office.Interop.Excel.Application)Marshal.GetActiveObject("Excel.Application");
        COMAddIn addIn = excelApplication.COMAddIns.Item(ref addInName);

        addIn.Object.AddinMethodName(params);

Also had to add a reference to Microsoft.Office.Core under COM and Excel.Interop under Assemblies.

score 0 · Answer 4 · answered Feb 13 '09 at 07:45

I assume that your method Foo somehow interacts with Excel. Otherwise you can just add a reference to the assembly containing the class with the Foo method and call it from there without instantiating Excel.

The only other way I can think is to get a reference to your CommandBarButton through the excelApp object. CommandBarButton has a method called Execute which is similar to clicking the button. Something like this:

        Excel.Application excelApp = new Excel.Application(); 
        CommandBarButton btn = excelApp.CommandBars.FindControl(...) as CommandBarButton;
        btn.Execute();

Thanks, that's a neat trick, but I was looking for a more general approach as beyond this simple test application we would have lots of methods, certainly some with parameters and so wouldn't want to create a hidden button for each of them (and how would parameters be handled). — Ben Robbins, Feb 13 '09 at 07:58

How to call a VSTO AddIn method from a separate C# project?

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