Table of Contents
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 the IT Mill Toolkit, and as it is included in
com.itmill.toolkit.ui.AbstractComponent
, all UI components
automatically support it.
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
GeneralEvent
s generated by
B
, but in
addition to this,
A
would also receive all
SpecializedEvent
s 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.
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