The old code failed to reliably detect new QScreens and connect their signals to its own slots. For example, if the QApplication added a new screen at the beginning of the screen list (which happens if the new screen is primary), the signal-connecting loop would actually instead add the now second screen to QDesktopWidget's list *again*, and connect its signals, but not connect any signal to the new, first screen. Furthermore, QDesktopWidget would miss geometry changes because QWidget (and hence QDesktopScreenWidget) automatically shrinks when the screen it is on gets smaller. To fix all of this, QDesktopScreenWidget now keeps its own record of the screen and its geometry, and it always scans over the entire screen list without relying on any ordering guarantees on behalf of QApplication. Change-Id: I2ee8361adf643849f43b7dd9a95966920fd13528 Task-number: QTBUG-52101 Reviewed-by: Błażej Szczygieł <spaz16@wp.pl> Reviewed-by: Marc Mutz <marc.mutz@kdab.com>