Proper way to manually set the layout of a window

[anda_skoa]

Or I can make all widgets in layout members of MainWindow class and access them directly.

That's the way to do it.
Member variables exist for the purpose of having access to data from all methods of an object.

However, I feel that neither of these is the right way.

Why? This is how object oriented language are designed to work.

Is there a way to pass the widgets to ui?

ui is a pointer to an object of a generated class.
You can of course derive from that class, add your additional members to that and then create an instance of it.

Or you use a second container object of a custom class.

Cheers,
_