Unable to debug project within solution when it is not the startup project

Question

I have an application that has a startup project (ProjectA) that runs another executable in another Project (ProjectB). When I start the solution with ProjectA as the startup project, I am unable to debug ProjectB. It is unable to load the PDB file even though it is in the directory where its searching.

However, when I start the application and ProjectB is the startup project, I am able to debug it. I assume this is because it is referencing the executable instead of the dll.

Why is this so? How do I get around this so that I can have ProjectA be the startup project and still debug ProjectB?

Answer 1

As I understand it, your Project A has started the Project B .exe. Something along these lines:

Public Class ProjectAForm
    Private Sub ButtonRunProjectB_Click(sender As Object, e As EventArgs) Handles ButtonRunProjectB.Click
        Process.Start("D:\Github\stackoverflow\multi-project-debugging\project-b\bin\Debug\netcoreapp3.1\project-b.exe")
    End Sub
End Class

You want to debug Project B in this context, but your debugger is attached only to Project A and not to Project B:

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Manual

The interactive way to go about it is with DEBUG\Attach to Process...

Now you will hit your breakpoints.

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Programmatic

Doing this automatically is tricky but possible. Refer to this answer:

Can I programmatically attach a running .NET 6 process to a running instance of Visual Studio debugger?

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Suggestion

If Project A doesn't reference Project B directly (that is, they're completely independent inside a common solution where Project A is the startup) I find that it saves a lot of confusion to have Project B build automatically (if needed) whenever Project A runs. Manually setting project-a to depend on project-b achieves this outcome.