There is no official API. You are free to copy-paste the code from the link I posted to your project.
On Wed, Jan 22, 2014 at 1:59 PM, Randahl Fink Isaksen <rand...@rockit.dk>wrote: > Hi Tomas > > Great idea! I can see how the InvalidationSubscriber idea would work – but > it is just a concept right? There is no official API for this, right? > > Randahl > > > > > > On 22 Jan 2014, at 13:34, Tomas Mikula <tomas.mik...@gmail.com> wrote: > > Hi Randahl, > > I'm curious about an example where you would take advantage of the > behavior where multiple addListener(listener) calls add the listener just > once. > > Anyway, here [1] are helper classes InvalidationSubscriber and > ChangeSubscriber that allow you to do that: > > InvalidationSubscriber subscriber = new InvalidationSubscriber(observable, > listener); > > subscriber.subscribe(); // registers the listener > subscriber.subscribe(); // no-op > > Cheers, > Tomas > > [1] https://gist.github.com/TomasMikula/8557825 > > On Wed, Jan 22, 2014 at 11:23 AM, Randahl Fink Isaksen > <rand...@rockit.dk>wrote: > >> Hi Martin >> >> While I agree your proposed solution would work, I still don’t understand >> why JavaFX should keep on supporting duplicates in listener collections. >> Can anyone come up with just 1 example of an application that might be >> depending on having two listeners on the same Observable? E.g. this kind of >> code: >> >> myObservable.addListener(myChangeListener); //add it >> myObservable.addListener(myChangeListener); //add it again >> >> In what kind of situation would this sort of code make any sense? >> >> If we all feel confident that the presence of duplicates listeners is >> always an error, I warmly recommend changing the API to be duplicate free. >> >> Yours >> >> Randahl >> >> >> >> >> On 22 Jan 2014, at 11:07, Martin Sladecek <martin.slade...@oracle.com> >> wrote: >> >> > Hi all, >> > I would like to start discussion about an addition to API in >> Observable, ObservableValue and all Observable collections. >> > There were multiple requests for a way how to avoid duplicates in >> listeners lists. The way RT-25613 solves this is that it introduces public >> boolean hasListener(ListenerType listener) which would return true if the >> provided listener is already registered. >> > >> > This has one significant drawback that all of Observable* are actually >> interfaces. Means we can only add hasListener as a defender method. The >> problem is with the default implementation. We cannot return anything >> meaningful, so we have to throw an UnsupportedOperationException. The >> problem is that this might blow up unexpectedly when some "older" >> Observable implementation is used. Also, it might be easy to miss when >> implementing the interface, since the IDE might not force you to implement >> it. >> > >> > So as an alternative solution, I propose adding something like: >> > >> > ensureListener(ListenerType listener) >> > >> > which would make sure the listener is on the list and if a listener is >> already present, the number of times listener is registered on the >> Observable will NOT grow after this call. >> > >> > The default implementation (for Observable) would look like this: >> > >> > public default void ensureListener(InvalidationListener listener) { >> > removeListener(listener); >> > addListener(listener); >> > } >> > >> > subclasses might do something more effective. The same would apply to >> ObservableValue and ChangeListener and Observable[List|Set|Map] and >> [List|Set|Map]ChangeListener. >> > >> > What do you think? >> > >> > JIRA link: https://javafx-jira.kenai.com/browse/RT-25613 >> > >> > -Martin >> >> > >
