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/ >>>>> >>>> >>>> >>>> >>> >> >
