Comment 1 DJ Houghton 2002-05-07 18:34:43 EDT

Listeners are added/changed/removed from the list based on identity. Are you 
sure that your listener is being removed/replaced? A good place to step into 
in debug mode would be ResourceChangeListenerList.add().

Here is a little test that I wrote which work ok. Is there something obvious 
which I am overlooking?

public void testMulti() {

	class Listener1 implements IResourceChangeListener {
		public boolean done = false;
		public void resourceChanged(IResourceChangeEvent event) {
			assertEquals("1.0", IResourceChangeEvent.POST_CHANGE, 
event.getType());
			done = true;
		}
	}

	class Listener2 extends Listener1 implements IResourceChangeListener {
		public void resourceChanged(IResourceChangeEvent event) {
			assertEquals("2.0", 
IResourceChangeEvent.POST_AUTO_BUILD, event.getType());
			done = true;
		}
	}

	Listener1 listener1 = new Listener1();
	Listener2 listener2 = new Listener2();

	getWorkspace().addResourceChangeListener(listener1, 
IResourceChangeEvent.POST_CHANGE);
	getWorkspace().addResourceChangeListener(listener2, 
IResourceChangeEvent.POST_AUTO_BUILD);

	try {
		project1.touch(getMonitor());
	} catch (CoreException e) {
		handleCoreException(e);
	}

	assertTrue("3.0", listener1.done);
	assertTrue("3.1", listener2.done);
	getWorkspace().removeResourceChangeListener(listener1);
	getWorkspace().removeResourceChangeListener(listener2);
}

Comment 2 Judah Diament 2002-05-08 09:20:50 EDT

your re-creation is a off on key points, but rather than address your example, 
let me point you to the exact place in the Eclipse code that is causing the 
problem.

I just ran through one execution of my code in the debugger, and here is exactly 
what is happening: my class, an instace of ProjectNavigatorContentProvider whose 
ID = 87 on this run of the code, added itself with eventMask = 16 (i.e. 
POST_AUTO_BUILD). My class sub-classses 
org.eclipse.ui.model.WorkbenchContentProvider. Now, here is a snippet of code 
that appears in WorkbenchContentProvider (I cut out most of the method - just 
showing the relevant part):

public void inputChanged(Viewer viewer, Object oldInput, Object newInput) {
		if (newWorkspace != null) {
			newWorkspace.addResourceChangeListener(this, 
IResourceChangeEvent.POST_CHANGE);
		}
	}
}
So, inside its inputChanged method, WorkbenchContentProvider registers itself 
with eventmask = 1. Since my sub-class, ProjectNavigatorContentProvider, doesn't 
have its own inputChanged method, the method in the super class is executed, and 
the debugger shows my instace, with ID = 87, registering itself with eventMask = 
1 (i.e. POST_CHANGE), and I am no longer registered for POST_AUTO_BUILD 
(eventMask = 16).

In short, the behavior of the code inside 
org.eclipse.core.internal.events.ResourceChangeListenerList.add(IResourceChangeL
istener, int) is to replace the old mask of the given listener with the new one, 
so despite the fact that in my constructor I am registering with eventMask = 16, 
every time inputChanged is called, 1 *replaces* 16 instead of 1 being *added to* 
16. 

Is that clearer?

Comment 3 John Arthorne 2002-05-08 10:51:41 EDT

Look at the javadoc for IWorkspace.addResourceChangeListener, here is a snippet 
from the first paragraph:

 * After completion of this method, the given listener will be 
 * registered for exactly the specified events.  If they were 
 * previously registered for other events, they will be deregistered.  

So we're behaving as spec'ed.  I suggest you override the inputChanged method 
from the superclass so that it doesn't override your previous listener 
registration.

Comment 4 Judah Diament 2002-05-08 10:56:37 EDT

John - I alrady made the change - my method is quite simple:
/**
 * @see IContentProvider#inputChanged(Viewer, Object, Object)
*/ 
public void inputChanged(Viewer arg0, Object arg1, Object arg2)
{
   super.inputChanged(arg0, arg1, arg2);
   ResourcesPlugin.getWorkspace().addResourceChangeListener(this, 
      IResourceChangeEvent.POST_AUTO_BUILD);
}

the real queston is - is that spec the most logical choice, or would adding the 
new eventMask to the old one be better? I agree that the knee-jerk reaction is 
that the spec is good, but when you consider the super/sub class example, one 
wonders if it would make more sense to add the new to the old instead of 
deleting the old....

Comment 5 DJ Houghton 2002-05-08 11:15:05 EDT

The problems in changing things are:
- when you want to change the events that you are listening for you would have 
to de-register your listener and then re-register
- changing the API is difficult at this point in time because there are a lot 
of people out there depending on the behaviour as documented

Comment 6 Judah Diament 2002-05-08 11:56:54 EDT

OK - just a thought for consideration in version 3, I guess. Minimally, you 
could add a new call - some like "changeListener" instead of "addListener" - 
which would allow people to update the eventMask instead of blowing it away.

Comment 7 DJ Houghton 2002-05-08 13:50:34 EDT

Closing for now. 
Will consider adding new API for merging resource change listener events post 
2.0.

Comment 8 DJ Houghton 2002-09-10 12:27:31 EDT

Renamed from:
super-class IResourceChangeListener registration kills sub-class registration

Reopening for consideration.

Comment 9 John Arthorne 2004-08-26 12:09:45 EDT

Closing bugs we don't plan to fix.