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https://issues.apache.org/jira/browse/WICKET-5677?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14100576#comment-14100576
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Carl-Eric Menzel commented on WICKET-5677:
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Updated with Martin's suggestions, turning it into an onReAdd that is called
when onInitialize is *not* used.
> Components should have onAdd to complement onRemove
> ---------------------------------------------------
>
> Key: WICKET-5677
> URL: https://issues.apache.org/jira/browse/WICKET-5677
> Project: Wicket
> Issue Type: Improvement
> Components: wicket
> Affects Versions: 6.16.0, 7.0.0-M2
> Reporter: Carl-Eric Menzel
> Assignee: Carl-Eric Menzel
>
> When a component is removed from the tree, onRemove is called on it and all
> its children, so they can do cleanup. When a component is added to the page,
> there is no similar call that could do initializations.
> Note: onInitialize sounds similar, but is actually rather different:
> onInitialize is called exactly once, the very first time the component is
> added to the page's component tree. It is basically a delayed constructor to
> allow superclasses to depend on (abstract) methods implemented by subclasses
> while giving the subclass's constructor a chance to run.
> onInitialize is not called again if a component is removed from the hierarchy
> and then added again. This happens, for example, in wizards, and in pages
> that replace panels to show different views.
> A good example is FencedFeedbackPanel, with the issue reported in
> WICKET-5265: in onRemove, the FFP clears the fence marker in its fence
> component. Stepping forward in a wizard where a step contains such an FFP
> causes onRemove to be called. Going backwards then re-adds the step panel and
> its FFP, but the fence is now broken, because the FFP has no way of knowing
> that it was re-added.
> I tried working around it using onConfigure and onBeforeRender. But due to
> the way Wicket traverses the component tree, it is not always guaranteed that
> this will be called soon enough, i.e. before an outer FFP has already
> "stolen" the feedback messages that should have been protected by the fence.
> I therefore propose adding a method onAddToPage that is called:
> - whenever a component or one of its parents is added to the page component
> tree, i.e. when it gets a connection to the page.
> - never more than once per add
> - never before the parent components are initialized.
> If a component is added to a container before the container is added to the
> page, this method should NOT be called - only when there is a path to the
> page.
> I have an implementation of this that is tested and fixes the problem in
> WICKET-5265. I'll push it to a branch as soon as I can. It's currently based
> on wicket-6.x but is easily portable to 7. It's not an API break, since only
> non-abstract methods are added.
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