An event, in general, is some change in state in discrete time that is induced by external or internal actions. An event action in Qt is an object that is inherited from the abstract QEvent class, which is a notification of something significant that has happened. Events become more useful in creating custom widgets on our own. An event can happen either within an application or as a result of an outside activity that the application needs to know about. When an event occurs, Qt creates an event object and notifies the instance of a QObject class or one of its subclasses through the event() function. Events can be generated from both inside and outside the application. For instance, the QKeyEvent and QMouseEvent objects represent some kind of keyboard and mouse interaction, and they come from the window manager. The QTimerEvent objects are sent to QObject when one of its timers fires, and they usually come from the operating system. The QChildEvent objects are sent to QObject...