WeakXXListener - when not to use?

[Jeanette Winzenburg]

good points, going into thinking :)

Maybe we can come up with a pattern (and its anti-pattern) about how  
to use them correctly, now that we are looking more closely (and are  
in the process of learning - me at least :) If we could collect the  
does and donts somewhere, it would be easier for contributors to do  
the-right-thing and watch out for the-wrong-thing.

Thanks!

Zitat von Kevin Rushforth <kevin.rushforth at oracle.com>:

> 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 doing something that is no longer valid (or computationally  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 ..
>>>
>>>
>>>
>>>