Re: [riena-dev] ListenerList vs ArrayList

[Stefan Liebig <Stefan.Liebig@xxxxxxxxxxxx>]

Several points:
- I think we are free to change (better extend) the behavior of our 
ListenerList to suit our needs
- the original ListenerList already was policy driven, so why not widen 
the policy if we need it?
- and again: what is the use case for adding a listener multiple times, 
and is this an indicator for some design flaw, unclear responsibilities, 
bla, bla, .. (don´t get me wrong, I am just asking)

Stefan

Christian Campo wrote:
> I think we should agree on something (either duplicates or not). Now 
> you, Elias, removed the ListenerList to allow duplicates while
> Thorsten just on monday replaced an ArrayList with the ListenerList.
>
> There should be a unique policy throughout Riena. I am sure what the 
> policy is in Eclipse. I thought the ListenerList that we use is just
> a copy of the class of Riena with an API that supports Generics. So 
> the "offiicial" class in Eclipse that should be used for Listeners 
> does not
> allow duplicates (or better it ignores them).
>
> If you ignore what could happen is that if you add the same listener 
> twice and then remove one, no listener is registered (since there is 
> no counter). So
> can a programmer know that a listener he wants to register (this 
> particular instance) is already registered ? If he can, then he is 
> doing something wrong
> registering it the second time. Its a little that we dont throw an 
> exception for duplicates then, but that is the way the Eclipse class 
> behaves.
>
> IMHO I think since the ListenerList exists we should use it for each 
> and every case where a Listener is required. Since the original 
> implementation from
> Eclipse ignores duplicates (and hence does not allow them), we could 
> think about throwing some kind of runtime exception and document that 
> duplicate
> listeners are not allowed.
>
> What do you guys think ?
>
> christian
>
>
> Am 27.08.2008 um 07:31 schrieb Stefan Liebig:
>
> > We could also extend ListenerList to allow duplicates. There is 
> > already an enum Mode that could be
> > extended for that.
> > However, does it make sense for a listener to be notified multiple 
> > times for the same event?
> >
> > Stefan
> >
> > Volanakis, Elias wrote:
> > > Just FYI, in the Tree/Table/List-Ridget I changed the container for the
> > > double click listeners to ArrayList (recently changed to ListenerList).
> > > The reason for using an ArrayList is that adding duplicate listeners is
> > > explicitly permitted there.
> > >
> > > This fixes the recent test failures in #testAddDoubleClickListener.
> > > Feel free to discuss if you disagree. The alternative is to adjust the
> > > tests / javadoc to disallow duplicate listeners.
> > >
> > > Thanks,
> > > Elias.
> > >
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