onEvent

OnEvent is a commonly used naming convention in event-driven programming for a method that handles a particular event. The exact meaning and signature of onEvent vary by framework, but the core idea is a callback that is invoked by an event dispatcher when the corresponding event occurs.

In many frameworks, an object subscribes to events by registering with an event source or event bus, and defines one or more handler methods. A method named onEvent may be called automatically when the event is delivered, optionally taking the event payload as a parameter. Some frameworks require explicit registration, others use annotations or naming conventions to discover handlers.

Common use cases include user interface events (button presses, mouse movements), I/O and network events, and completion or error notifications from asynchronous tasks.

Design considerations: the method name onEvent is not universal; the actual signature depends on the framework. It may be invoked on a particular thread, requiring synchronization. Depending on the architecture, handlers may be unregistered to avoid leaks, and event ordering and delivery guarantees differ.

See also: event-driven programming, event bus, observer pattern.