Call TlbExp to make a type library that is embedded in the .xll

[Sergey-Vlasov]

For .NET 6, dscom need to be installed on the development machine:
https://github.com/dspace-group/dscom

And for .NET 6, a COM interface should be explicitly declared, not using ClassInterfaceType.AutoDual.

[govert]

And for .NET 6, a COM interface should be explicitly declared, not using ClassInterfaceType.AutoDual.
Do you think AutoDispatch still works?

[Sergey-Vlasov]

Do you think AutoDispatch still works?

How can I test for it?

For development, I tested with NET6DnaComServer project and NET6Book.xlsm.

The book includes a function call and two macros:

    Sub TestLateBound()
        Dim dnaComServer As Object
        Dim hello As String
        Dim result As Double
    
        Set dnaComServer = CreateObject("DnaComServer.ComLibrary")
        hello = dnaComServer.ComLibraryHello()
        result = dnaComServer.Add(1, 2)
    
        Debug.Print hello, result
    End Sub
    
    Sub TestEarlyBound()
        Dim dnaComServer As NET6DnaComServer.ComLibrary
        Dim hello As String
        Dim result As Double
    
        Set dnaComServer = New NET6DnaComServer.ComLibrary
        hello = dnaComServer.ComLibraryHello()
        result = dnaComServer.Add(1, 2)
    
        Debug.Print hello, result, "E"
    End Sub

The function and both macros worked.

[govert]

Yes I think that code can only work if the IDispatch interface is implemented.
I think it will fail if you put ClassItnerfaceType.None.

I also think that AutoDual still works the same way under .NET 6 as under Framework - it's just that the dscom tool chose not to support it (which I think is fine, for the problematic reasons they point to.)

[Sergey-Vlasov]

I also think that AutoDual still works the same way under .NET 6 as under Framework - it's just that the dscom tool chose not to support it (which I think is fine, for the problematic reasons they point to.)

It is not only dscom. In .NET 6 build, I got
warning CS0618: 'ClassInterfaceType.AutoDual' is obsolete: 'Support for IDispatch may be unavailable in future releases.'

And there is CA1408: Do not use AutoDual ClassInterfaceType
https://docs.microsoft.com/en-us/visualstudio/code-quality/ca1408?view=vs-2022&tabs=csharp

[Sergey-Vlasov]

Yes I think that code can only work if the IDispatch interface is implemented. I think it will fail if you put ClassItnerfaceType.None.

In NET6DnaComServer/AddIn.cs:

    [ComVisible(true)]
    [ClassInterface(ClassInterfaceType.None)]
    public class ComLibrary : IComLibraryInterface

[govert]

I'm actually super confused. See my answer here: https://groups.google.com/g/exceldna/c/onRDZLJwoBY
I had discovered the issue when making the CTP work under .NET 6. This was the crucial information: dotnet/winforms#4370 (comment)
For the UserControl (the context in both the CTP and the WinForms issue above) it does not work to mark the derived class as AutoDispatch. You have to implement an interface and mark it as the ComDefaultInterface. Apparently this is needed for the IDispatch to be created. The way I'm reading it, the IDispatch is no longer made using reflection (so is made at compile time in the interface case, so still works?) But then what about your example above? Perhaps something to do with the base class. The UserControl class is no longer marked as ComVisible in .NET 5/6. So having a base class that is not ComVisible (so was not compiled knowing that it would need to support IDispatch might break the AutoDispatch by requiring the reflection-based implementation which is no longer supported.

Anyway, it's worth taking note of these quirks, especially about the CTP controls. I forgot about the problem and fix I found in February, just that I had tried it under .NET 6 and did get it to work.

[govert]

I think your example:

    [ComVisible(true)]
    [ClassInterface(ClassInterfaceType.None)]
    public class ComLibrary : IComLibraryInterface

work because of the interface, where the default is then to generate an IDispatch.