foxtrot.utils

Class EventListenerProxy

java.lang.Object

foxtrot.utils.EventListenerProxy

All Implemented Interfaces:

java.lang.reflect.InvocationHandler

public class EventListenerProxy
extends java.lang.Object
implements java.lang.reflect.InvocationHandler

This class wraps an EventListener subclass (and thus any AWT/Swing event listener such as ActionListeners, MouseListeners and so on) making sure that if a wrapped listener is executing, another wrapped listener (even of different type) it is not executed.
For example, if a user clicks very quickly on a button, it may trigger the execution of the associated listener more than once. When the listener contains Foxtrot code, the second click event is dequeued by Foxtrot and processed again, invoking the listener again. Using this class to wrap the listener avoids this problem: the second event will be dequeued and processed by Foxtrot as before, but the wrapped listener will not be called.
Example Usage:

 final JButton apply = new JButton("Apply");
 apply.addActionListener((ActionListener)EventListenerProxy.create(ActionListener.class, new ActionListener()
 {
    public void actionPerformed(ActionEvent e)
    {
       apply.setEnabled(false);
       Worker.post(new Job()
       {
          public Object run()
          {
             // Lenghty apply code
          }
       });
    }
 }));

 JButton cancel = new JButton("Cancel");
 cancel.addActionListener((ActionListener)EventListenerProxy.create(ActionListener.class, new ActionListener()
 {
    public void actionPerformed(ActionEvent e)
    {
       // For example, dispose a dialog
    }
 }));
 

Without using EventListenerProxy, when a user clicks on the apply button and immediately after on the cancel button, it happens that apply's button listener is executed; in there, usage of Foxtrot's Worker will dequeue and execute the event associated to the cancel button click, that will - for example - dispose the dialog before the apply operation is finished.
When using EventListenerProxy instead, the second event - the cancel button click - will not be executed: the event will be processed without invoking the wrapped listener.
The overhead in the code is to change plain listeners:

 button.addActionListener(new ActionListener() {...});
 

to this:

 button.addActionListener((ActionListener)EventListenerProxy.create(ActionListener.class, new ActionListener() {...}));
 

Version:

$Revision: 1.3 $

Field Summary

Fields

Modifier and Type	Field and Description
private java.util.EventListener	listener
private static boolean	working This flag signals the fact that the wrapped listener is in execution.

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	EventListenerProxy(java.util.EventListener listener) Creates an instance that wraps the given listener

Method Summary

Methods

Modifier and Type	Method and Description
static java.util.EventListener	create(java.lang.Class listenerInterface, java.util.EventListener listener) Creates a proxy for the given listener.
java.lang.Object	invoke(java.lang.Object proxy, java.lang.reflect.Method method, java.lang.Object[] args)

Methods inherited from class java.lang.Object

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

Field Detail

working

private static boolean working

This flag signals the fact that the wrapped listener is in execution. It is static since event listeners are never processed in parallel, but one after the other in the Event Dispatch Thread. Only after one listener finishes another one can execute.

listener

private java.util.EventListener listener

Constructor Detail

EventListenerProxy

protected EventListenerProxy(java.util.EventListener listener)

Creates an instance that wraps the given listener

Method Detail

create

public static java.util.EventListener create(java.lang.Class listenerInterface,
                             java.util.EventListener listener)

Creates a proxy for the given listener.
The listener must implement the given listener interface

Parameters:

listenerInterface - The interface used to create the proxy

listener - The listener to proxy

Returns:

A proxy for the given listener

Throws:

java.lang.NullPointerException - When the interface or the listener is null

java.lang.IllegalArgumentException - When the listener does not implement the interface

invoke

public java.lang.Object invoke(java.lang.Object proxy,
                      java.lang.reflect.Method method,
                      java.lang.Object[] args)
                        throws java.lang.Throwable

Specified by:

invoke in interface java.lang.reflect.InvocationHandler

Throws:

java.lang.Throwable