[jira] [Commented] (WICKET-3789) visitChildren and friends require inner classes. Replace with iterators

["Christoph Leiter (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/WICKET-3789?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13451900#comment-13451900 ] 

Christoph Leiter commented on WICKET-3789:
------------------------------------------

What happened to ComponentHierarchyIterator<T>? As it is now it doesn't support a generic type and its Iterator always returns Component.
                
> visitChildren and friends require inner classes. Replace with iterators
> -----------------------------------------------------------------------
>
>                 Key: WICKET-3789
>                 URL: https://issues.apache.org/jira/browse/WICKET-3789
>             Project: Wicket
>          Issue Type: Improvement
>            Reporter: Juergen Donnerstag
>            Assignee: Juergen Donnerstag
>         Attachments: wicket-3789.patch
>
>
> I never really liked that we need inner classes (implementations of IVisitor) for traversing the component hierarchy. When needed, it comes easily to me that I need MarkupContainer.visitChildren(), but I always need to look up how to use it and friends.  Debugging is also more complicated than it has to (breakpoint inside the visit function: either another breakpoint behind visitChildren or "press the continue-until-end-of-method" key several times until you are back). For these reasons I gave Iterators another try. I've attached a patch for others to review and provide feedback. I've also added test cases (ComponentIteratorTest) and I changed quite some visitChildren occassions in core. Maven compiles and successfully executes all tests.
> I put the new classes in org.apache.wicket.util.iterator
> ComponentIterator - An enhanced iterator with filters. Also supports chaining iterators. Builder API for class filters, isvisible filters, isenabled filters etc. Supports Java for each.
> ComponentHierarchyIterator - enhances ComponentIterator to provide hierarchy traversal. Adds traversal filters to separate traversal control from what next() returns. Same Builder API. Supports Java for each.
> IteratorFilter - Simple abstract class to implement the filter conditions. The Builder API makes use of it to add filters to the iterator. 
> Some examples:
> ComponentHierarchyIterator iter = new ComponentHierarchyIterator(page);
> while (iter.hasNext())
> {
> 	Component component = iter.next();
> }
> for (Component component : new ComponentHierarchyIterator(page))
> {
> }
> new ComponentHierarchyIterator(page)
>      .filterLeavesOnly()
>      .filterByVisibility()
>      .filterByClass(Form.class)
> iter.skipRemainingSiblings();  // skip all remaining component of the same parent
> iter.dontGoDeeper()  // provided the current component is a container and potentially has children, they are ignored
> onEndOfSiblings() is a callback function if you want to be informed about the iterator leaving a level

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