there are other places that should be checked though. for example
before we invoke a listener on the component we should check again to
make sure that visibility hasnt changed. eg if visibility depends on
some property of the user clicking the link that changed between
render and clicking the link.
-igor
On Tue, Nov 30, 2010 at 8:30 AM, Pedro Santos <pedros...@gmail.com> wrote:
> An implementation idea:
>
> Component {
> public final void configure()
> {
> if (!getFlag(FLAG_CONFIGURED))
> {
> setVisible_NoClientCode(isVisible()); //we only check the user
> isVisible in here
> onConfigure();
> setFlag(FLAG_CONFIGURED, true);
> }
> }
> }
>
> On Tue, Nov 30, 2010 at 2:16 PM, Igor Vaynberg <igor.vaynb...@gmail.com>wrote:
>
>> 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
>> >
>>
>
>
>
> --
> Pedro Henrique Oliveira dos Santos
>
