c# enumerable class - compatible with VBA

Question

Can anyone instruct me on how to code a C# enumerable class such that the \"for each\" construct in Excel VBA works properly? I tried this out with a test class called Peop

Answer 1

I came across this thread in Feb 2020 whilst experiencing the same problem with a class I wrote as a wrapper for a C# Dictionary.

The get enumerator method in the class is

    public IEnumerator GetEnumerator()
    {
        foreach (KeyValuePair<dynamic, dynamic> myPair in MyKvp)
        {
            yield return new dynamic[] { myPair.Key, myPair.Value };
        }
    }

I found that the DispId(-4) was successful when I added the attribute to the signature in the Interface.

Before (in interface)

IEnumerator GetEnumerator();

Which prodeced an object does not know this methos error in VBA

After (in interface)

[DispId(-4)]
IEnumerator GetEnumerator();

This update allowed me to iterate using a For Each loop in VBA.

Answer 2

Try adding [DispId(-4)] to your GetEnumerator() method. This flags it to be the DISPID_NEWENUM member. In order for VBA to work with a collection using For Each, it needs to implement _newEnum via COM.

This can be done by implementing an Enumerator and attributing it with the proper DispId. This is typically done via implementing a custom interface with this specified, though there are other mechanisms available.