How to use separate threads for pushbuttons in QT (like SwingWorker in Java)

[anda_skoa]

if I put connect before start of thread (I need click button twice so it incorrect in principle as it was without nested concnet())

You need to connect before start or risk missing the signal.
Usually we want our programs to work reliably, but if you can live with your program sometimes not working then keep it the way you are connecting now.

Anyway as in other way. there is bad_alloc, despite I put Lister::listed2 on heap memory: bad_alloc is when I put in the end
delete Lister::listed2; I need probably uqual it to Null.

Whatever listed2 is, it is likely already using heap allocation internally, so that wouldn't change anything anyway,

Maybe you are running out of memory.

Cheers,
_