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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