An event is a way for a class to provide notifications to listeners when a particular thing happens.
An event is a way to notify listeners when a particular thing occurs. In the object-oriented paradigm, an event is a way for a class to provide notifications to clients of that class when some interesting thing happens to an object. The most familiar use for events is in graphical user interfaces; typically, the classes that represent controls in the interface. These classes have events that are notified when the user does something to the control (for example, click a button).
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See also: signals-slots