# Poco::XML

# class TreeWalker

Library: XML
Package: DOM
Header: Poco/DOM/TreeWalker.h

## Description

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.

## Member Summary

Member Functions: accept, currentNode, expandEntityReferences, filter, firstChild, getCurrentNode, lastChild, next, nextNode, nextSibling, operator =, parentNode, previous, previousNode, previousSibling, root, setCurrentNode, whatToShow

## Constructors

### TreeWalker

TreeWalker(
const TreeWalker & walker
);

Creates a TreeWalker by copying another TreeWalker.

### TreeWalker

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

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

## Destructor

### ~TreeWalker

~TreeWalker();

Destroys the TreeWalker.

## Member Functions

### currentNode

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.

### expandEntityReferences

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.

### filter

NodeFilter * filter() const;

The NodeFilter used to screen nodes.

### firstChild

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.

### getCurrentNode

Node * getCurrentNode() const;

See currentNode().

### lastChild

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.

### nextNode

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.

### nextSibling

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.

### operator =

TreeWalker & operator = (
const TreeWalker & walker
);

Assignment operator.

### parentNode

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.

### previousNode

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.

### previousSibling

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.

### root

Node * root() const;

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

### setCurrentNode

void setCurrentNode(
Node * pNode
);

Sets the current node.

### whatToShow

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.

### accept

int accept(
Node * pNode
) const;

### next

Node * next(
Node * pNode
) const;

### previous

Node * previous(
Node * pNode
) const;