Shall I use a thread?
No.
Does anybody can help with this issue?
I think "grabing" keyboard input is the only thing Qt can do for you, see: http://qt-project.org/doc/qt-5/qwidg...l#grabKeyboard
Hence Qt can't help you if you want to write a key logger. If you want to log keys, have a look at the source code of other key logger applications.