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

[anda_skoa]

But in this case, the slot must receive an object of type QueryResult.

Yes, I should have written updateView(const QueryResult&), but I thought it would be pretty obvious that the signal would need to transport the data as its argument.

Qt greatly limits how signals and slots can use parameters

In what way?

and the one way I can see, is to use a Signal Mapper

Why on earth would you need a signal mapper?

But even with Signal Mapper, I don't know how to properly use it to say, emit a signal from one object with a QString as param, and capture and use the sent QString in a slot in another object.

You would not use a signal mapper when you can use a trivial signal/slot connection between two objects.

I browsed net heavily, I could not find a complete working example of it.

Heavly for how many seconds?
The first Google hit on signal/slots is the Qt documentation on that topic (which should be the primary source even without search engine help) and it does naturally have an example that transports a value through the connection.

Which class here should inherit from QThread?

The suggestion was to use moveToThread() of the worker object which does not require subclassing QThread.

Cheers,
_

[Cupidvogel]

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

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

[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,
_