For example, if a user clicks a Close button, we probably want the window's close() function to be called. More generally, we want objects of any kind to be able to communicate with one another. In GUI programming, when we change one widget, we often want another widget to be notified. Signals and slots are made possible by Qt's meta-object system. The signals and slots mechanism is a central feature of Qt and probably the part that differs most from the features provided by other frameworks. Signals and slots are used for communication between objects.
