Debugging VB6 project that calls a .Net(C#) dll

Question

I have been stump in this problem for a few hours now. I hope someone has had a similar problem to this.

We have developed a prototype .Net(C#) dll using VS2010, and would like to be able to call this dll in a both C# applications and VB6 application.

My question is:

Is it possible to debug a VB6 application that is calling a .Net dll? I get an error message "Automation Error The system cannot find the file specified"

The error message suggests that there is something missing for my VB6 app to find the .Net dll.

I am aware that if the VB6 application has been compiled, and the .exe has been created, the VB6 will successfully call the .Net dll functionality when using the .exe

However it is important that we can debug through our VB6 application. Unfortunately debugging does not allow you to step over the line of code instantiating the .Net DLL's class object. I can't seem to do this.

NOTE: I have looked around forums and MSDN documentation and I mostly find solution for calling a VB6 dll in .NET; which is unfortunately the opposite of what we need to do.

NOTE: I have already registered the compiled .Net(C#) assembly, and referenced it in the VB6 project.

I have however found these two pages, which seemed to be what we need, but its a solution for calling a .NET(c#) dll generated using VS2005. This doesnt seem to work when the .NET(C#) dll was generated using VS2010.

site1 site2

If someone could give any suggestions or direct me somewhere I can get one, that would be great.

Thanks

SOLUTION Thanks to @HansPassant, I have found the solution. To debug a VB6 project that contains a C# .NET assembly, you need to register the .NET dll through both "regasm" and "gacutil", then make sure to close and reopen the VB6 application before you start debugging.

Answer 1

This is not a problem, VB6 uses its own debugger that doesn't get in the way of any other debugger, including the managed one for C# code.

You start from your C# class library project, ensure it is selected as the start project. Project + Properties, Debug tab. Select the "Start external program" option and enter the path to the VB6 IDE. Typically c:\program files\microsoft visual studio\vb98\vb6.exe. Set a breakpoint on the method you want to debug.

Press F5 and the VB6 ide will start running. Load or create your vb6 project. Note how you can add the path to the .vbp project in the previous step so it will automatically load your project.

Start debugging your vb6 project as usual. As soon as it starts using your [ComVisible] C# class then your C# assembly gets loaded. And the breakpoint will hit when your vb6 code calls the method. Switch back and forth as needed. Note that you cannot single-step from vb6 to C# code, you have to set breakpoints to get the debugger to stop.