I want to save the focused window's title, i made this part but i dont know is there any QEvent which catches all (non-application) focusChanged event? Like switching from Chrome to Qt Creator. I made an alternative solution that checks in every second if the topmost window title has changed but this is so rude. I need cross-platform solution if possible.
EDIT
I am using QT 5.9.0
Quick answer: Qt only has focus events for it's own windows and widgets. See http://doc.qt.io/qt-5/qfocusevent.html#details for start point. There is no event for focus in other applications.
Details: For multi-platform solution is needed to have more general point of view. On some (X window) systems where keyboard focus is in window under mouse. But that window becomes topmost only after click. On Mobile platforms there is only one active application. And application is not allowed seeing when other applications are activated. So in my understanding there is no full multi-platform solution.
Windows only extensions are in the Qt Windows Extras. http://doc.qt.io/qt-5/qtwinextras-overview.html. But there is nothing focus change related unfortunately.