[WICKET-3789] visitChildren and friends require inner classes. Replace with iterators

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Won't Fix
• Assignee: Juegen Donnerstag
• Reporter: Juegen Donnerstag
• Created: 13/Jun/11 14:07
• Updated: 18/Dec/13 13:34
• Resolved: 18/Dec/13 13:34

Description

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

Issue Links

• is related to: WICKET-5284 Too deep recursion in AbstractHierarchyIterator