Rails spinoffs - Mar 2008 - Replace existing handlers for the same element+event pair or not?

Hi there,

 I need some help to undestand what is goin on with this event handler
and if I need or not the feature of replace existing hadlers when
observing an event.

  From Prototype docs in Element.observe():
 "...It does not replace existing handlers for that same element+event
pair. It adds to the list of handlers for that pair. Using observe
will never incapacitate earlier calls. ..."

  That is a good thing but...

 I have a component (read div element with some sub elements) which
observes onKeyDown when is loaded. The element initializer registers
as handler to call a just previously installed function (of that very
element).

  As reaction of a key down event the handler executes an updater on
the element (executes an updater on itself). As the updated div has
the same #id, I was expecting the observation to remain valid after
the updater do its job but, when user press a second time a key on it,
it isn''t reacting with the handler (is not calling again that
updater).

  So I''ve interpreted that observations are not valid after and
updater execution so I''ve used the onComplete handler of the updater
to make a re-initialization of that DOM element after the updates.
That way, it registers the event observation again for the same element
+event pair with the same handler.

  Doing that the result was I have an always incremental quantity of
updater requests reacting to the key down (shoot in the foot).

  A kind of lazy solution will be to have a way to query an element if
it is already observing an event with some provided handler and make
an observation only if it is not observing that already. That way
onComplete can be used to always initialize and register the
observations without worry of previous observations of that event
+handler pair.

  A more elegant solution is to observe just once like I did in first
place but I''m unable to figure out why isn''t working after the
fisrt
updater.

 Updaters brings a  new element instance and deletes the original
object? if so (and besides the incremental thing) why using onComplete
to initialize again the element after the updater was making 2 updater
requests instead of one after the first updater?

  Any clue?

  thanks,

Sebastian



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You could try observing an object higher up the chain that you don''t  
replace. If you are observing a keydown event, that''s global to the  
window, right?

Walter

On Mar 22, 2008, at 3:33 PM, Sebastian Sastre wrote:
>
> Hi there,
>
> [snip]
>   As reaction of a key down event the handler executes an updater on
> the element (executes an updater on itself). As the updated div has
> the same #id, I was expecting the observation to remain valid after
> the updater do its job but, when user press a second time a key on it,
> it isn''t reacting with the handler (is not calling again that
> updater).
>
>   So I''ve interpreted that observations are not valid after and
> updater execution so I''ve used the onComplete handler of the
updater
> to make a re-initialization of that DOM element after the updates.
> That way, it registers the event observation again for the same  
> element
> +event pair with the same handler.
>
>
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Hi Walter,

  making aside the problem of misplaced responsabilities in parent
components, I''ve tested what you propose. For the record: the result
was exactly the same.

  So after that I was searching a way to extend prototype''s objects so
I can observe an event only if not previously observed (making another
observation method with this feature). In the middle of that (failed)
process I''ve realized that making with every updater a #stopObserving
and #observe again, the event should be hooked only once. And it did
it.

  I don''t know what is going on there but for now I''ve solved
my
problem.

  My guess is about some trouble between the updated instance and the
observed event for it.

  thanks anyway,

Sebastian



On Mar 22, 4:57 pm, Walter Lee Davis
<wa...-HQgmohHLjDZWk0Htik3J/w@public.gmane.org>
wrote:
> You could try observing an object higher up the chain that you
don''t  
> replace. If you are observing a keydown event, that''s global to
the  
> window, right?
>
> Walter
>
> On Mar 22, 2008, at 3:33 PM, Sebastian Sastre wrote:
>
>
>
> > Hi there,
>
> > [snip]
> >   As reaction of a key down event the handler executes an updater on
> > the element (executes an updater on itself). As the updated div has
> > the same #id, I was expecting the observation to remain valid after
> > the updater do its job but, when user press a second time a key on it,
> > it isn''t reacting with the handler (is not calling again that
> > updater).
>
> >   So I''ve interpreted that observations are not valid after
and
> > updater execution so I''ve used the onComplete handler of the
updater
> > to make a re-initialization of that DOM element after the updates.
> > That way, it registers the event observation again for the same  
> > element
> > +event pair with the same handler.
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