WeakXXListener - when not to use?

[Kevin Rushforth]

Yes, that's another good point about weak listeners, although in 
practice it might not be much of a problem unless the listener is doing 
something that is no longer valid (or computationally expensive, but 
that is less likely).

Another problem is that using weak listeners can let you avoid thinking 
about the life cycle of the object and the listener. In cases where 
there is a good point to explicitly free the listener, it is often 
better to do so.

In most of the cases of skins, it's probably OK to remove the listener 
as long as there is no functional problem with the listener disappearing 
some unknowable amount of time after the object in question goes away.

> if not doing that "doSomethingUseful" would cause a - more - terrible
> misbehavior than a memory leak, would that mean that the
> listening/update implementation in that specific case would have to be
> re-thought? F.i. in the case of the ButtonSkin listening to control's
> scene is changing global state which might be broken if it's not
> reverted to not having a default/cancel registered? (what a horrible
> sentence, sry ;)

Yes, something like that is what I meant. And the rethinking might lead 
to a need for an explicit removal of the listener at the "right time", 
or adding additional cleanup logic when the skin goes away.

-- Kevin


On 3/26/2020 4:58 AM, Nir Lisker wrote:
> BTW, Tomas Mikula wrote about this on
> http://tomasmikula.github.io/blog/2015/02/10/the-trouble-with-weak-listeners.html
> .
> There is a comment at the end that is worth a read too.
>
>
> On Thu, Mar 26, 2020 at 1:53 PM Jeanette Winzenburg <fastegal at swingempire.de>
> wrote:
>
>> Zitat von Kevin Rushforth <kevin.rushforth at oracle.com>:
>>
>> Thanks for your input!
>>
>> Glad we didn't miss the "minimum bar" height - with the java doc being
>> really clear on that :)
>>
>> What I still don't quite get is the concern about "too early" and "not
>> cleaning up" - maybe I misunderstand the point entirely
>>
>>> As for whether the above is sufficient, it depends on what the
>>> listener does (what its purpose is).In this simple example, it seems
>>> unlikely that removing the listener when the instance of SomeClass
>>> goes out of scope will cause any problems. It's worth looking at
>>> what "doSomethingUseful" does to see if unregisters anything that
>>> ought to be unregistered (and now maybe won't be if the listener
>>> goes away early).
>>>
>> if not doing that "doSomethingUseful" would cause a - more - terrible
>> misbehavior than a memory leak, would that mean that the
>> listening/update implementation in that specific case would have to be
>> re-thought? F.i. in the case of the ButtonSkin listening to control's
>> scene is changing global state which might be broken if it's not
>> reverted to not having a default/cancel registered? (what a horrible
>> sentence, sry ;)
>>
>> Hmm ..
>>
>>
>>
>>