so how is it different if they can still override something that needs
to be checked all the time?
-igor
On Tue, Nov 30, 2010 at 8:02 AM, Pedro Santos <pedros...@gmail.com> wrote:
> I understand the concern about possible isVisible implementations like
>
> isVisible(return currentlyTime < 10:00:00;) //imagine this component being
> rendered at 09:59:59
> isVisible(return dao.list().size() > 0);// performance issues
>
> But maybe we can have the best from both approaches. This is an copy/paste
> from java.awt.Component:
>
> public boolean isVisible() {
> return isVisible_NoClientCode();
> }
> final boolean isVisible_NoClientCode() {
> return visible;
> }
>
> There are some points in the awt framework were the isVisible method is not
> used in benefit of isVisible_NoClientCode
> I'm in favor of create an final isVisible/Enabled version and change the
> Wicket core to use it. Also maintain the hotspot to users provide their
> isVisible/Enable implementations that will serve to feed the core component
> state.
>
> On Mon, Nov 29, 2010 at 4:56 PM, Igor Vaynberg <igor.vaynb...@gmail.com>wrote:
>
>> ive run into plenty of weird problems with overrides, but maybe
>> because this was in a high concurrency app where data changed
>> frequently. the problems arise from the fact that the value returned
>> from isvisible() can change while we are doing traversals, etc.
>>
>> eg we run a traversal for all visible components and put them in a
>> list. later we iterate over the list and try to render these
>> components. the render function also checks their visibility and if
>> they are no longer visible it throws an exception.
>>
>> if isvisible() override depends on some external factor like the
>> database there is a small window where the value can change and now
>> you can have a weird exception: such as "tried to invoke a listener on
>> a component that is not visible or not enabled". these are very
>> intermittent and damn near impossible to reproduce.
>>
>> another problem is performance. isvisible() is called multiple times
>> during the request and if it depends on the database it can be a
>> performance problem. in fact a couple of users have complained about
>> this on the list in the past. at least now we have an easy solution
>> for them - use onconfigure().
>>
>> so as of right now the developers have two choices: override
>> isvisible() and potentially suffer the consequences. or, override
>> onconfigure() and set visibility there in a more deterministic
>> fashion.
>>
>> -igor
>>
>>
>>
>> On Mon, Nov 29, 2010 at 10:21 AM, Eelco Hillenius
>> <eelco.hillen...@gmail.com> wrote:
>> > To expand, unless I'm missing something (new?), things are really only
>> > problematic when both the mutable value and the override are mixed. In
>> > a way, I think that using the override is 'more pure', as it's a
>> > simple function that is executed when needed, whereas mutable state
>> > can be harder to deal with when trying to figure out how it got to be
>> > in that state. So, sorry Igor, but we disagree on this one.
>> >
>> > Eelco
>> >
>> >
>> > On Mon, Nov 29, 2010 at 10:13 AM, Eelco Hillenius
>> > <eelco.hillen...@gmail.com> wrote:
>> >> Niether is evil. It has potential pitfalls, which you should just be
>> >> aware of. We use such overrides all over the place and never have
>> >> problems with them either. :-) Avoiding it is safer, but also more
>> >> verbose (in 1.3.x at least).
>> >>
>> >> Eelco
>> >>
>> >> On Mon, Nov 29, 2010 at 9:49 AM, Igor Vaynberg <igor.vaynb...@gmail.com>
>> wrote:
>> >>> On Mon, Nov 29, 2010 at 9:35 AM, Sven Meier <s...@meiers.net> wrote:
>> >>>> Hi Douglas,
>> >>>>
>> >>>> WICKET-3171 describes a problematic case, where visibility of a
>> >>>> component changes while its form is being processed.
>> >>>> In our projects we're overriding isVisible() where appropriate and
>> never
>> >>>> encountered a similar problem.
>> >>>>
>> >>>> I'd say WICKET-3171 is the rare 5% usecase. What's next, is overriding
>> >>>> isEnabled() going to be declared evil too? ;)
>> >>>
>> >>> yes
>> >>>
>> >>> -igor
>> >>>
>> >>>>
>> >>>> Sven
>> >>>>
>> >>>> On Mon, 2010-11-29 at 11:22 -0600, Douglas Ferguson wrote:
>> >>>>
>> >>>>> Can you explain why? We have done this all over the place.
>> >>>>>
>> >>>>> D/
>> >>>>>
>> >>>>> On Nov 29, 2010, at 10:00 AM, Martin Grigorov wrote:
>> >>>>>
>> >>>>> > The recommended way since a few 1.4 releases is to override
>> onConfigure()
>> >>>>> > and call setVisible(true|false) depending on your conditions.
>> >>>>> >
>> >>>>> > On Mon, Nov 29, 2010 at 4:49 PM, Douglas Ferguson <
>> >>>>> > doug...@douglasferguson.us> wrote:
>> >>>>> >
>> >>>>> >> Igor posted a comment to this bug saying that overriding
>> isVisible() is
>> >>>>> >> "evil"
>> >>>>> >>
>> >>>>> >> https://issues.apache.org/jira/browse/WICKET-3171
>> >>>>> >>
>> >>>>> >> I was surprised by this and am curious to hear more.
>> >>>>> >>
>> >>>>> >> D/
>> >>>>>
>> >>>>
>> >>>>
>> >>>>
>> >>>
>> >>
>> >
>>
>
>
>
> --
> Pedro Henrique Oliveira dos Santos
>
