Package com.vaadin.event

Provides classes and interfaces for the inheritable event model. The model supports inheritable events and a flexible way of registering and unregistering event listeners. It's a fundamental building block of Vaadin, and as it is included in AbstractComponent, all UI components automatically support it.

Package Specification

The core of the event model is the inheritable event class hierarchy, and the EventRouter which provide a simple, ubiquitous mechanism to transport events to all interested parties.

The power of the event inheritance arises from the possibility of receiving not only the events of the registered type, but also the ones which are inherited from it. For example, let's assume that there are the events GeneralEvent and SpecializedEvent so that the latter inherits the former. Furthermore we have an object A which registers to receive GeneralEvent type events from the object B. A would of course receive all GeneralEvents generated by B, but in addition to this, A would also receive all SpecializedEvents generated by B. However, if B generates some other events that do not have GeneralEvent as an ancestor, A would not receive them unless it registers to listen for them, too.

The interface to attaching and detaching listeners to and from an object works with methods. One specifies the event that should trigger the listener, the trigger method that should be called when a suitable event occurs and the object owning the method. From these a new listener is constructed and added to the event router of the specified component.

The interface is defined in MethodEventSource, and a straightforward implementation of it is defined in EventRouter which also includes a method to actually fire the events.

All fired events are passed to all registered listeners, which are of type ListenerMethod. The listener then checks if the event type matches with the specified event type and calls the specified trigger method if it does.