Extendable / customisable UI using Designer

I don't know if it makes sense..

Is it possible for a UI to 'inherit' from another UI? (By UI, I mean the generated UI class for a .ui designer form)

Basically, I have to create multiple dialogs, which have some common content, and some separate content as well.
Normally, I want to keep the common content in a 'base class', and inherit the other dialogs from the common dialog.

Is this possible using Qt Designer and form files?

you can use QUiLoader to load ui files at runtime, don't know if that is what you are looking for

Depending on your layouting needs, maybe but the base components into widgets and then use these in your dialogs?

Most simple way is to use the "promote widget" feature on a place holder widget.

Cheers,
_