The event you are looking for is QEvent::ApplicationDeactivate
: "The application has been suspended, and is unavailable to the user".
You can install an event filter on your QApplication
instance to catch this event. See the documentation for QObject::installEventFilter(QObject*)
for more details how this works.
Since Qt 5.2 the QEvent::ApplicationDeactivate
event is deprecated. The correct way to identify when an application is deactivated in Qt 5.2 (or later) is to use the QGuiApplication::applicationStateChanged(Qt::ApplicationState state)
signal.