Richard Bolkey – Blog

<?xml version="1.0" encoding="UTF-8"?>
<ul xmlns:t="http://tapestry.apache.org/schema/tapestry_5_1_0.xsd">
 
    <!-- The custom delegate to the component to render based on the context of the current node. -->
    <t:nodedelegate to="currentNodeRenderer"/>
 
    <t:block>
        <!-- This block contains a set of components to delegate rendering to based on the current node. -->
        <div t:id="blackNode">
            <!-- Delegate to the child component to render.  This replaces the component's body. -->
            <t:nodedelegate to="currentNodeRenderer"/>
        </div>
 
        <div t:id="redNode">
            <t:nodeDelegate to="currentNodeRenderer"/>
        </div>
 
    </t:block>
 
</ul>

public class Tree {
 
    @Parameter(required = true)
    private Node node;
 
    @Component(id = "blackNode", parameters = {"node=currentNode", "childPosition=currentChildPosition"})
    private RenderBlackNode blackNode;
 
    @Component(id = "redNode", parameters = {"node=currentNode", "childPosition=currentChildPosition"})
    private RenderRedNode redNode;
 
    private Node currentNode;
 
    private Map<Node, Integer> childPositions;
 
    public Node getCurrentNode() {
        return currentNode;
    }
 
    public void setCurrentNode(final Node node) {
        // set the initial child position for the node to 0 if it has not been seen yet.
        if (!childPositions.containsKey(node)) {
            childPositions.put(node, 0);
        }
        this.currentNode = node;
    }
 
    public int getCurrentChildPosition() {
        return childPositions.get(this.currentNode);
    }
 
    public void setCurrentChildPosition(final int pos) {
        this.childPositions.put(currentNode, pos);
    }
 
    /**
     * Selects the Node component to render based on the currentNode type.
     *
     * @return the component to render the current node
     */
    public BaseRenderNode getCurrentNodeRenderer() {
        BaseRenderNode object = null;
        if (currentNode instanceof BlackNode) {
            object = blackNode;
        }
        else if (currentNode instanceof RedNode) {
            object = redNode;
        }
        return object;
    }
 
    void setupRender() {
        childPositions = CollectionFactory.newMap();
        setCurrentNode(node);
    }
}

<?xml version="1.0" encoding="UTF-8"?>
<div xmlns:t="http://tapestry.apache.org/schema/tapestry_5_1_0.xsd">
    <!-- The body is replaced with component(s) for the child nodes. -->
    <t:body/>
</div>

public class BaseRenderNode {
 
    @Parameter(required = true, cache = false)
    private Node node;
 
    @Parameter
    private int childPosition;
 
    @SetupRender
    boolean setup() {
        // prevents rending with the node parameter is null.
        return node != null;
    }
 
    @BeforeRenderBody
    boolean beforeChild() {
        // the node  has children, render the body to render a child
        final boolean render = node.getChildren().size() > 0;
 
        if (render) {
            // sets the container's currentNode to the node's child at the given index.
            node = node.getChildren().get(childPosition);
        }
        return render;
    }
 
    @AfterRenderBody
    boolean afterChild() {
        // increment the child position, afterRender on the child will have the container's currentNode set back to the node before the body was rendered.
        childPosition = childPosition + 1;
        // return true on last child index, finishing the iteration over the children, otherwise re-render the body (to render the next child)
        return node.getChildren().size() <= childPosition;
    }
 
    @AfterRender
    void after() {
        // set the currentNode to the parent after render (pop the stack)
        if (!node.isRoot())
            node = node.getParent();
    }
}