Events are a well known concept in graphical user interface (GUI) models, although they can be used in many contexts. The purpose of events is to notify an application about changes in the components used by the application. In a GUI environment, for example, an event might be the click on a button. Your application might be registered to this button and thus be able to execute certain code when this button is clicked.
The OpenOffice.org event model is similar to the JavaBeans event model. Events in OpenOffice.org are, for example, the creation or activation of a document, as well as the change of the current selection within a view. Applications interested in these events can register handlers (listener interfaces) that are called when the event occurs. Usually these listeners are registered at the object container where the event occurs or to the object itself. These listener interfaces are named
Event listeners are subclasses of com.sun.star.lang.XEventListener that receives one event by itself, the deletion of the object to which the listener is registered. On this event, the listener has to unregister from the object, otherwise it would keep it alive with its interface reference counter.
|Important! Implement the method disposing() to unregister at the object you are listening to and release all other references to this object.|
Many event listeners can handle several events. If the events are generic, usually a single callback method is used. Otherwise, multiple callback methods are used. These methods are called with at least one argument: com.sun.star.lang.EventObject. This argument specifies the source of the event, therefore, making it possible to register a single event listener to multiple objects and still know where an event is coming from. Advanced listeners might get an extended version of this event descriptor struct.
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