Add user defined function to Visual Studio Excel Add-in

Question

In visual studio I have an Excel 2010 Add-in project. How can I have that project create the following module:

Answer 1

A VSTO addin can't create UDF's, so you need to create a separate addin for the functions. Although this addin can be in the same DLL as the VSTO addin, you cannot communicate between the VSTO and the UDF's without special trickery.

I have a blog post about this. It gives you a complete example project that includes VSTO and UDF's.

Here is the basic structure of the UDF itself.

[Guid("3B81B6B7-3AF9-454F-AADF-FAF06E5A98F2")]
[InterfaceType(ComInterfaceType.InterfaceIsDual)]
[ComVisible(true)]
public interface IFunctions
{
    int MYINT();
}

[Guid("F58C591D-A22F-49AD-BC21-A086097DC26B")]
[ClassInterface(ClassInterfaceType.None)]
[ComVisible(true)]
public class Functions : IFunctions 
{
    public int MYINT()
    {
        return 42;
    }
}