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From "Michael Wooten (JIRA)" <j...@apache.org>
Subject [jira] Created: (LANG-580) Add Event Support Utilities
Date Mon, 04 Jan 2010 17:05:54 GMT
Add Event Support Utilities
---------------------------

                 Key: LANG-580
                 URL: https://issues.apache.org/jira/browse/LANG-580
             Project: Commons Lang
          Issue Type: New Feature
          Components: General
    Affects Versions: 3.0
         Environment: Java SE 5.0+
            Reporter: Michael Wooten
            Priority: Minor
             Fix For: 3.0


I would like to propose some support be added to Lang for basic event handling. This would
be based on the way that PropertyChangeSupport can be used to add and remove listeners and
post events. 

Add interface EventSupport<L extends EventListener> 

addListener(L listener)
The signature for the method that can add a listener of some subtype of EventListener

removeListener(L listener)
The signature for the method that can remove a listener of some subtype of EventListener

Add class AbstractEventSupport implements EventSupport<L>, Iterable<L>

AbstractEventSupport(Object eventSource)
Constructs a new AbstractEventSupport object and associates it with the object that will be
used as the source of all events (much like PropertyChangeSupport).

addListener(L)
An implementation that adds a listener to an internal collection.

removeListener(L)
An implementation that removes a listener from an internal collection.

iterator()
Returns an iterator over the attached listeners.

getSource()
Returns a reference to the source object of all events.

The best way to describe this would be to demonstrate an example of how it can be used.

public class ButtonPressedEventSupport extends AbstractEventSupport<ButtonPressedListener>
{

    public ButtonPressedEventSupport(Object source) { super(source); }

    public void fireButtonPressed(Button button) {
        ButtonPressedEvent bpe = new ButtonPressedEvent(getSource(), button);
        for (ButtonPressedListener listener : this)
        {
            listener.buttonPressed(bpe);
        }
    }
}

public class MyWindow implements EventSupport<ButtonPressedListener> {
     private final ButtonPressedEventSupport buttonPressedEventSupport;

     public MyWindow { buttonPressedEventSupport = new ButtonPressedEventSupport(this); }

     public void addListener(ButtonPressedListener listener) { buttonPressedEventSupport.addListener(listener);
} 

     public void removeListener(ButtonPressedListener listener) { buttonPressedEventSupport.removeListener(listener);
} 

     ...

    private void onDetectButtonPressed(Button button) {
        buttonPressedEventSupport.fireButtonPressed(button);
    }
}

I haven't compiled the above code. It's just an example of how these classes could be used
so that you're not constantly rewriting the code and interfaces for adding and removing listeners,
and it provides a fairly easy method of creating methods to fire events.

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