eu.webtoolkit.jwt
Class Signal

java.lang.Object
  eu.webtoolkit.jwt.AbstractSignal
      eu.webtoolkit.jwt.Signal

public class Signal
extends AbstractSignal

A signal that propagates events to listeners.

A signal implements the Observer pattern, allowing one or more listeners to listen for events generated on the signal.

For a usage example take a look the documentation of Signal2.

Nested Class Summary

static interface

Signal.Listener The listener interface.

Nested classes/interfaces inherited from class eu.webtoolkit.jwt.AbstractSignal

AbstractSignal.Connection

Constructor Summary

Signal()
Creates a new signal.

Signal(WObject sender)

Method Summary

AbstractSignal.Connection	addListener(WObject listenerOwner, Signal.Listener listener) Adds a listener for this signal.
void	removeListener(Signal.Listener listener) Removes a listener.
void	trigger() Triggers the signal.

Methods inherited from class eu.webtoolkit.jwt.AbstractSignal

getListenerCount, getListeners, isBlocked, isConnected, setBlocked

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Signal

public Signal()

Creates a new signal.

Signal

public Signal(WObject sender)

Method Detail

addListener

public AbstractSignal.Connection addListener(WObject listenerOwner,
                                             Signal.Listener listener)

Description copied from class: AbstractSignal

Adds a listener for this signal.

Each listener will be notified when the signal is triggered.

An owner object may be passed when the listener is implemented using an (anonymous) inner class. In that case the owner object should be the enclosing object of the listener object, and this is used to bind the lifetime of the listener. To avoid the owner object from not being garbage collected when it is no longer used, only the owner object will add a reference to the listener, while the signal will use a weak reference.

This avoids the most common reason for memory leaks in Java implementations of the Observer pattern: the owner object will not get garbage collected because of the (anonymous) listener object having a reference to it, even if the receiver object is no longer referenced from anywhere. When the owner object is not null, the listener is stored using a strong reference in the owner object, and using a weak reference in the signal.

Specified by:

addListener in class AbstractSignal

Parameters:

listenerOwner - if not null, the enclosing object for a listener implemented using an inner class

listener - the listener

Returns:

a connection object that may be used to control the connection

removeListener

public void removeListener(Signal.Listener listener)

Description copied from class: AbstractSignal

Removes a listener.

Specified by:

removeListener in class AbstractSignal

Parameters:

listener - a listener that was previously added.

trigger

public void trigger()

Triggers the signal.

The Signal.Listener.trigger() method of all listeners added to this signal is invoked, unless the signal is blocked (see AbstractSignal.setBlocked(boolean).