Navigation
XPathNavigator also supports a robust set of navigational methods that are more comprehensive than those of XmlDocument and XmlReader. This next list shows that we can move backward and forward to any node of any type of the document with ease.
- MoveTo
- MoveToAttribute
- MoveToFirst
- MoveToFirstAttribute
- MoveToFirstChild
- MoveToFirstNamespace
- MoveToID
- MoveToNamespace
- MoveToNext
- MoveToNextAttribute
- MoveToNextNamespace
- MoveToParent
- MoveToPrevious
- MoveToRoot
We bring back our venerable purchase order document from previous articles to demonstrate the XPathNavigator API. I added a few extra items to the order document shown in Listing 1 to provide a better demonstration of XPathNavigator's capabilities.
Listing 1: PO.xml Purchase Order
<?xml version="1.0" encoding="utf-8" ?> <po:PurchaseOrder xmlns:po="http://michalk.com/ XmlDOM/PO.xsd" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"> <Number>1001</Number> <OrderDate>8/12/01</OrderDate> <BillToAddress> <Street>101 Main Street</Street> <City>Charlotte</City> <State>NC</State> <ZipCode>28273</ZipCode> </BillToAddress> <ShipToAddress> <Street>101 Main Street</Street> <City>Charlotte</City> <State>NC</State> <ZipCode>28273</ZipCode> </ShipToAddress> <LineItem Name="Computer Desk" Description="Wood desk for computer" SKU="12345A123" Price="499.99" Qty="1" /> <LineItem Name="Monitor" Description="Computer Monitor 19-Inch" SKU="19A123" Price="299.99" Qty="1" /> <LineItem Name="Computer" Description="Pentium 4 Computer" SKU="411111" Price="999.99" Qty="1" /> <LineItem Name="Mouse" Description="Computer Mouse" SKU="233B1" Price="49.99" Qty="1" /> </po:PurchaseOrder>
Our first sample program in Listing 2 navigates through all the elements, attribute and text nodes of the documents displaying pertinent information about them. It starts out by loading the PO.xml file from disk into an XPathDocument and executes MoveToRoot to move the cursor to the root node of the document. From there it passes XPathNavigator to the recursive WalkNode static method of our demo class. This method displays the current node that the XPathNavigator cursor points to and walks through all the attributes to display them. It also recursively calls WalkNode for each child node to continue the process recursively. Attributes are accessed with the MoveToNextAttribute method calls. Child nodes are accessed using the MoveToFirstChild method first to position the first child and MoveToNext to cycle through the rest of the siblings. The MoveToParent call is used to jump back up to the parent of the attribute or child node. The output from the console is shown in Listing 3.
Listing 2: XPathNavigator Navigation Demo Code
using System; using System.Xml; using System.Xml.XPath; namespace XmlDotNet { public class XPathNavDemo { public static void Main() { // load the PO XPathDocument doc = new XPathDocument("PO.xml"); // retrieve the navigator XPathNavigator nav = doc.CreateNavigator(); // move navigator cursor to root node of document nav.MoveToRoot(); // recursively walk the nodes of the root node WalkNode(nav, 0); } public static void WalkNode(XPathNavigator nav, int depth) { // display the node information in a pretty format DisplayNode(nav, depth); // process child attribute nodes if (nav.HasAttributes) { // loop through all the attributes of the // current node // and display them while(nav.MoveToNextAttribute()) DisplayNode(nav, depth+1); // move back to the parent element node of the // attribute nodes nav.MoveToParent(); } // process child element nodes if (nav.HasChildren) { // move to the first child of the // current node nav.MoveToFirstChild(); // recursively display the first child node // and its subnodes WalkNode(nav, depth+1); // loop through the rest of the siblings // recursively while (nav.MoveToNext()) WalkNode(nav, depth+1); // move back to the original parent node nav.MoveToParent(); } } // push the text over to the right to make printing pretty public static void PrintDepth(int depth) { for (int i=0; i < depth; i++) Console.Write(" "); } // display node information public static void DisplayNode(XPathNavigator nav, int depth) { // push the text over to the right to make // printing pretty PrintDepth(depth); // display a node value for only text and // attribute nodes string val = ""; if (nav.NodeType == XPathNodeType.Attribute || nav.NodeType == XPathNodeType.Text) { val = nav.Value; } Console.WriteLine("Name:{0} Type:{1} Value:{2}", nav.Name, nav.NodeType, val); } } }
Listing 3: XPathNavigator Navigation Demo Results
Name: Type:Root Value: Name:po:PurchaseOrder Type:Element Value: Name:Number Type:Element Value: Name: Type:Text Value:1001 Name:OrderDate Type:Element Value: Name: Type:Text Value:8/12/01 Name:BillToAddress Type:Element Value: Name:Street Type:Element Value: Name: Type:Text Value:101 Main Street Name:City Type:Element Value: Name: Type:Text Value:Charlotte Name:State Type:Element Value: Name: Type:Text Value:NC Name:ZipCode Type:Element Value: Name: Type:Text Value:28273 Name:ShipToAddress Type:Element Value: Name:Street Type:Element Value: Name: Type:Text Value:101 Main Street Name:City Type:Element Value: Name: Type:Text Value:Charlotte Name:State Type:Element Value: Name: Type:Text Value:NC Name:ZipCode Type:Element Value: Name: Type:Text Value:28273 Name:LineItem Type:Element Value: Name:Name Type:Attribute Value:Computer Desk Name:Description Type:Attribute Value:Wood desk for computer Name:SKU Type:Attribute Value:12345A123 Name:Price Type:Attribute Value:499.99 Name:Qty Type:Attribute Value:1 Name:LineItem Type:Element Value: Name:Name Type:Attribute Value:Monitor Name:Description Type:Attribute Value:Computer Monitor 19-Inch Name:SKU Type:Attribute Value:19A123 Name:Price Type:Attribute Value:299.99 Name:Qty Type:Attribute Value:1 Name:LineItem Type:Element Value: Name:Name Type:Attribute Value:Computer Name:Description Type:Attribute Value:Pentium 4 Computer Name:SKU Type:Attribute Value:411111 Name:Price Type:Attribute Value:999.99 Name:Qty Type:Attribute Value:1 Name:LineItem Type:Element Value: Name:Name Type:Attribute Value:Mouse Name:Description Type:Attribute Value:Computer Mouse Name:SKU Type:Attribute Value:233B1 Name:Price Type:Attribute Value:49.99 Name:Qty Type:Attribute Value:1