class Poco::XML::TreeWalker

Overview

TreeWalker objects are used to navigate a document tree or subtree using the view of the document defined by their whatToShow flags and filter (if any). More…

#include <TreeWalker.h>

class TreeWalker
{
public:
    // construction

    TreeWalker(
        Node* root,
        unsigned long whatToShow,
        NodeFilter* pFilter = 0
        );

    TreeWalker(const TreeWalker& walker);

    // methods

    TreeWalker&
    operator=(const TreeWalker& walker);

    Node*
    root() const;

    unsigned long
    whatToShow() const;

    NodeFilter*
    filter() const;

    bool
    expandEntityReferences() const;

    Node*
    currentNode() const;

    Node*
    getCurrentNode() const;

    void
    setCurrentNode(Node* pNode);

    Node*
    parentNode();

    Node*
    firstChild();

    Node*
    lastChild();

    Node*
    previousSibling();

    Node*
    nextSibling();

    Node*
    previousNode();

    Node*
    nextNode();

protected:
    // methods

    int
    accept(Node* pNode) const;

    Node*
    next(Node* pNode) const;

    Node*
    previous(Node* pNode) const;
};

Detailed Documentation

TreeWalker objects are used to navigate a document tree or subtree using the view of the document defined by their whatToShow flags and filter (if any).

Any function which performs navigation using a TreeWalker will automatically support any view defined by a TreeWalker.

Omitting nodes from the logical view of a subtree can result in a structure that is substantially different from the same subtree in the complete, unfiltered document. Nodes that are siblings in the TreeWalker view may be children of different, widely separated nodes in the original view. For instance, consider a NodeFilter that skips all nodes except for Text nodes and the root node of a document. In the logical view that results, all text nodes will be siblings and appear as direct children of the root node, no matter how deeply nested the structure of the original document.

A TreeWalker can be directly instantiated using one of its constructors - the DocumentTraversal interface is not needed and therefore not implemented. Unlike most other DOM classes, TreeWalker supports value semantics.

If the TreeWalker ‘s current node is removed from the document, the result of calling any of the movement methods is undefined. This behavior does not conform to the DOM Level 2 Traversal specification.

Construction

TreeWalker(
    Node* root,
    unsigned long whatToShow,
    NodeFilter* pFilter = 0
    )

Creates a TreeWalker over the subtree rooted at the specified node.

TreeWalker(const TreeWalker& walker)

Creates a TreeWalker by copying another TreeWalker.

Methods

TreeWalker&
operator=(const TreeWalker& walker)

Assignment operator.

Node*
root() const

The root node of the TreeWalker, as specified when it was created.

unsigned long
whatToShow() const

This attribute determines which node types are presented via the TreeWalker.

The available set of constants is defined in the NodeFilter interface. Nodes not accepted by whatToShow will be skipped, but their children may still be considered. Note that this skip takes precedence over the filter, if any.

NodeFilter*
filter() const

The NodeFilter used to screen nodes.

bool
expandEntityReferences() const

The value of this flag determines whether the children of entity reference nodes are visible to the iterator.

If false, they and their descendants will be rejected. Note that this rejection takes precedence over whatToShow and the filter. Also note that this is currently the only situation where NodeIterators may reject a complete subtree rather than skipping individual nodes.

To produce a view of the document that has entity references expanded and does not expose the entity reference node itself, use the whatToShow flags to hide the entity reference node and set expandEntityReferences to true when creating the iterator. To produce a view of the document that has entity reference nodes but no entity expansion, use the whatToShow flags to show the entity reference node and set expandEntityReferences to false.

This implementation does not support entity reference expansion and thus always returns false.

Node*
currentNode() const

The node at which the TreeWalker is currently positioned.

Alterations to the DOM tree may cause the current node to no longer be accepted by the TreeWalker ‘s associated filter. currentNode may also be explicitly set to any node, whether or not it is within the subtree specified by the root node or would be accepted by the filter and whatToShow flags. Further traversal occurs relative to currentNode even if it is not part of the current view, by applying the filters in the requested direction; if no traversal is possible, currentNode is not changed.

Node*
getCurrentNode() const

See currentNode().

void
setCurrentNode(Node* pNode)

Sets the current node.

Node*
parentNode()

Moves to and returns the closest visible ancestor node of the current node.

If the search for parentNode attempts to step upward from the TreeWalker ‘s root node, or if it fails to find a visible ancestor node, this method retains the current position and returns null.

Node*
firstChild()

Moves the TreeWalker to the first visible child of the current node, and returns the new node.

If the current node has no visible children, returns null, and retains the current node.

Node*
lastChild()

Moves the TreeWalker to the last visible child of the current node, and returns the new node.

If the current node has no visible children, returns null, and retains the current node.

Node*
previousSibling()

Moves the TreeWalker to the previous sibling of the current node, and returns the new node.

If the current node has no visible previous sibling, returns null, and retains the current node.

Node*
nextSibling()

Moves the TreeWalker to the next sibling of the current node, and returns the new node.

If the current node has no visible next sibling, returns null, and retains the current node.

Node*
previousNode()

Moves the TreeWalker to the previous visible node in document order relative to the current node, and returns the new node.

If the current node has no previous node, or if the search for previousNode attempts to step upward from the TreeWalker ‘s root node, returns null, and retains the current node.

Node*
nextNode()

Moves the TreeWalker to the next visible node in document order relative to the current node, and returns the new node.

If the current node has no next node, or if the search for nextNode attempts to step upward from the TreeWalker ‘s root node, returns null, and retains the current node.