API REVIEW: Weak event handler

Sven Reimers sven.reimers at gmail.com
Wed Jun 13 05:29:56 PDT 2012

Alright. Makes perfect sense for me.



On Wed, Jun 13, 2012 at 2:27 PM, Lubomir Nerad <lubomir.nerad at oracle.com> wrote:
> Hi Sven,
> in NetBeans they chose a different approach. Each weak event listener they
> create needs to hold a reference to the "source" on which it has been
> registered. First this requirement prevents it from being used with multiple
> sources and then it is prone to errors because the API allows to use
> different source during weak event handler creation and its registration.
> The nice thing is that their weak listeners handle everything internally and
> so their containers don't need to be aware about their existence.
> If we wanted to use this approach for weak event handlers, we would require
> to provide and store more information for each event handler (source,
> eventType, isHandlerOrFilter) which would complicate weak event handler
> construction even further and increase possibilities for incorrect usage.
> In my proposal I create only a simple weak event handler wrapper, which does
> very little work. It can be registered in the same way as any other event
> handler (even on multiple sources). But it requires its containers to be
> aware of its existence and handle it specially. Most use cases won't require
> do distinguish between EventHandler and WeakEventHandler, we need to have
> additional API for it only to provide possibility for adding (by external
> developers) new event handler containers (advanced use cases) which can
> handler weak event handlers correctly.
> Thanks,
> Lubo
> On 6/12/2012 10:28 PM, Sven Reimers wrote:
>> Ok. Here is a link to the JavaDoc how NetBeans handles this for
>> PropertyChanges
>> http://bits.netbeans.org/dev/javadoc/org-openide-util/org/openide/util/WeakListeners.html
>> I still do not understand the necessity for creating a new interface,
>> it contains no additional information (API) - for the user it can only
>> be used as an EventListener (assuming there will be no API explicitly
>> requiring WeakEventListener)..
>> Regards
>> Sven
>> On Tue, Jun 12, 2012 at 10:01 PM, Richard Bair<richard.bair at oracle.com>
>>  wrote:
>>> Hi Lubo,
>>>> I also considered to define the WeakEventHandler as an interface which
>>>> extends EventHandler, but adds no additional methods. Then leave it to event
>>>> handler containers to reference such event handlers weakly. This has very
>>>> simple and direct usage, but also its own problems. We can discuss it
>>>> further if you find this solution preferred to the wrapper approach.
>>> Extending WeakReference and lacking the public constructor did make me a
>>> little weak in the knees :-). What were the problems with WeakEventHandler
>>> being an interface?
>>> Thanks!
>>> Richard

Sven Reimers

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