Cannot capture Key_Up

[wysota]

Everything is set to default.

I'm assuming the MainWindow and centralwidget() configuration do something to intercept the Up/Down Keys.

Default focus policy of QWidget (and QMainWindow as well) is NoFocus.

Your widget simply doesn't have focus so it won't receive key events. If you want something to happen on a specific key combination you can register a shortcut for that combination - this is done via QShortcut (of course you still won't receive a keyPressEvent in your widget).