Qt multithreading and let the second thread update the main (UI) thread

[anda_skoa]

Can you give an example of how without using signal mapper I can transport a parameter, say, an object belonging to a custom class?

What is it with you and the signal mapper? There is no indication of any need for a signal mapper.
Declare a signal with the respective type as its argument type.

Which object do I need to move to thread? My Query Action class?

Well, the object that you want to run in the other thread.
Probably the instance of your QueryFinder class.

Cheers,
_