I use Qt4.3.3 on Windows Vista. If I re-implement QCoreApplication::notify in my application class in the trivial way which just passes every event back to QCoreApplication::notify then an infinite loop occurs as soon as the event loop is entered. Using the Visual Studio debugger I could only figure out that lots of timer events would occur again and again.

Background: My application presents a QSplitter view and I need to know when one of the QSplitter children is activated in the sense that one of its nested children receives the keyboard focus. I had hoped to solve this by using notify to catch all mouse press events anywhere in the QSplitter children.

QWorkspace/QMdiArea supposedly must solve this same problem, to keep track of the currently "active" sub-window, but I couldn't find out so far how they achieve this.