I see two disadvantages: order and exception handling for the detach methods.
The order /could/ be checked using pmd or aop, but that is something
we can't enforce, from a framework point of view a no-go IMO.
Now you rely on your users to properly ensure that all detach methods
are called, and especially the super().
Can't we come up with a better, automagic way of ensuring detach is
called, that is independent of the call hierarchy?
If it is only searching for IDetachable and calling detach on it, why
not walk the object graph and find all non-transient fields that
implement IDetachable and call detach?
Martijn
On 11/9/06, Igor Vaynberg <[EMAIL PROTECTED]> wrote:
after having implemented the annotations and thought about this some more, i
think i ended up patching the problem instead of fixing it.
there are a couple of problems with annotations that i now see:
a) we are not removing the overridible listeners from the api, so
annotations are just an alternative approach.
b) annotations have poor api visibility - unless you know about them its
very likely you are not going to find them
the reason why we have things like
Component.internalAttach()+Component.internalOnAttach()+Component.onAttach()
is that for methods like these the call to super() is very important.
in init methods like onattach() it must be the first thing that is called.
int cleanup methods like ondetach() it must be the last thing to be called.
i think a more proper fix to the problem would be to properly document these
and leave it to the users to implement properly. that way we can get rid of
the annotations and get back some api clarity by remoing
Component.internalAttach() and Component.internalOnAttach() and moving that
code into component.onattach().
now this is problematic because it is easy to forget to call super, and
there is a lot of existing code out there that doesnt. i think what we can
do is either create an aspect to check for the calls to super that is loaded
only during devel mode, or create an inspector for a static analysis tool
like pmd or findbugs to look for the error.
i think this will be a better solution then relying on annotations.
in the end the user has to know the consquences when overriding a method. us
trying to do as much as possible for the user only takes it part way - to
the Component level. But what if you extend Component and need to override
onAttach()? and then then another user subclasses this component? then the
problem of calling super is still there, we just deferred it for our
framework internal classes.
what do you think?
-igor
On 10/27/06, Igor Vaynberg <[EMAIL PROTECTED]> wrote:
>
> we have a couple of great candidate callbacks to be implemented with
> annotations instead of template methods. namely onattach/detach,
> onbegin/endrender
>
> what makes them great candidates is this
>
> 1) when implementing one you must always call super()
> this is not _always_ true. when extending a core component you dont need
> to because we have our own internalattach() we can use and onattach() is
> just an empty template.
>
> but when extending a non-core component you must call super() because you
> never know if that component uses it or not and it is very very unlikely
> that it is a behavior you want to override
>
> 2) implementors of onattach(), if they are good, will make it final and
> provide another breakout template to ensure their onattach code cannot be
> messed with. this leads you to have
>
> public final void onAttach(){ dosomething(); onAttach2(); } public void
> onAttach2() {}
>
> this is the general java pattern that i find very ugly personally, take a
> look at our Component.internalAttach() impl :)
>
> so what i propose is that we provide some annotations
> @OnAttach @OnDetach @OnBeforeRender @OnAfterRender
>
> users can annotate any number of methods with these and have them called.
>
> im sure there are other places that can benefit from this, but for now we
> can cleanup the mess that is internalAttach(), internalOnAttach()
> onAttach(), etc
>
> of course this is wicket 2.0 only
>
> -Igor
>
>
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