Firstform cannot be blank

I cannot set firstform in project properties as blank.It always set to top form after i save the project.
I use sub main() to navigate forms in project, since firstform is always being set to top form, then, that form _onshow event always be executed when the app running.

Any idea?

AppStudio requires that you have a firstform. You could add a form called frmBlank and have that be your first.