A software event represents an occurrence that a program can observe and handle, such as a key press, timer expiry or completed operation. It may carry data identifying what happened, where and to which object. An event handler performs the relevant response; an event loop commonly dispatches pending events to their destinations.
In Qt, an event object is delivered to a target object whose event method dispatches to a type-specific handler. Mouse, keyboard, resize and timer events carry different information.[ref] A queued event can be handled after the original occurrence, so event time and handling time differ. Reentrant or asynchronous handlers must also account for changes in application state between those moments.
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