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https://issues.apache.org/jira/browse/WICKET-6663?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16832318#comment-16832318
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Hans Schäfer commented on WICKET-6663:
--------------------------------------
Hi,
a detailed description of the implementation that broke follows:
I have a component "search"-Panel that hast two sub-components: a search-field
and a search-result-Panel. The search-field has an AjaxBehavior on "keyup" with
throttling (800ms). So the Ajax-Processing of this AjaxBehaviour is triggered
when the user stops entering the search term. In this case the search takes
place and the search-result-Panel updates its search-results. If there are no
search-results, the panel is invisible.
Seems to be straight-forward to be implemented inside this one AjaxBehaviour,
but there is a hard constraint: The backend that I have to use for searches is
slow. Sometimes it takes several seconds until it answers. This lead to a
blocking search-field in the straight-forward first implementation.
So I decoupled the steps that had to be done:
# Update the search-term on the server-side
# Do the search against the slow backend
# Update the search-result.
I realized this by introducing additional elements:
# A IRequestMapper/IRequestHandler-Pair for processing the search: This pair
is *not* processing a component-tree: it just receives the search-term, and
calls a Spring-Service that does the search against the slow backend. The
service caches the search result (using spring caching).
# A simple AjaxBehavior, that makes the Search-Result-Panel invisible, if
there are no search results. It makes the Search-Result-Panel visible if there
are search results. And it rerenders the Search-Result-Panel if onEvent is
called.
The AjaxBehavior for event "keyup" on the search-field now does the following:
Update the search-term on the server-side. Then return a Java-script that does
the following: call the IRequestHandler (1) for processing the search term
asynchronously. When this request returns successfully, fire the Ajax-Event on
the AjaxBehavior (2), that rerenders the Search-Result-Panel. This rerendering
ist fast, because the Search-Result-Panel gets the Search-Results form the
cache (uses the same Spring-Service).
Short summary: My visible sarch-field generates a script, that executes an Url
for a component that is potentially invisible.
Best regards
Hans
> Don't prevent requests on component placeholders (revert WICKET-6575)
> ---------------------------------------------------------------------
>
> Key: WICKET-6663
> URL: https://issues.apache.org/jira/browse/WICKET-6663
> Project: Wicket
> Issue Type: Bug
> Components: wicket-core
> Affects Versions: 8.1.0
> Reporter: Hans Schäfer
> Priority: Major
>
> Hello!
> WICKET-6575 introduced a bug in my application.
> I explicitly make an Ajax-Call to an invisible component. In my case: this
> component displays search results as soon as they are available. The call is
> triggered by a script created by another (visible) component.
> The method "canCallListener" already models the behavior of
> components/behaviors regarding invocations. If you make Ajax-Calls to
> invisible components you can hook in here (the default-Implementation causes
> an exception if component is invisible) and make processing possible. This
> was a consistent server-side API until Wicket-6575.
> Please remove the changes of Wicket-6575.
> Thanks
> Hans
>
>
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