[jira] Commented: (WICKET-3229) Removing Child in IVisitor affects traversal

["Igor Vaynberg (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/WICKET-3229?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12966951#action_12966951 ] 

Igor Vaynberg commented on WICKET-3229:
---------------------------------------

i think i would rather throw concurrentmodificationexception on add/remove. but honestly, this comes up so rarely that i think a javadoc note is enough.

> Removing Child in IVisitor affects traversal
> --------------------------------------------
>
>                 Key: WICKET-3229
>                 URL: https://issues.apache.org/jira/browse/WICKET-3229
>             Project: Wicket
>          Issue Type: Bug
>          Components: wicket
>    Affects Versions: 1.4.12
>            Reporter: Jacob Brookover
>            Priority: Minor
>         Attachments: WICKET-3229.patch
>
>   Original Estimate: 0.5h
>  Remaining Estimate: 0.5h
>
> Created a Panel that provides it's own dynamically created markup stream, scans that stream for wicket:ids, and adds different components based on the id.  Recently, I've been wanting to redraw this panel via AJAX, changing the markup and adding and removing child components accordingly.
> I tried to remove multiple stale components (e.g. a component that was generated from the previous markup but doesn't exist in the new markup) using an IVisitor..
> visitChildren(new IVisitor<Component>() {
>   public Object component(Component component) {
>     if (/* component is stale */)
>       component.remove();
>     return CONTINUE_TRAVERSAL_BUT_DONT_GO_DEEPER;
> }
> The IVisitor just does a simple run through an array and removing the component adjusted the size/count of the array, messing up the traversal and preventing other components from being removed.
> Potential Solutions:
> 1.  Throw an exception if the hierarchy is modified in an IVisitor.
> 2.  Use another means of traversing the children that allows addition/removal and still ensures visiting all the children.

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