How Do I...Handle Namespaces in XPath Queries with XmlNamespaceManager?

This sample shows how to select namespace specific XML data from an XmlDocument. It demonstrates the use of the XmlNamespaceManager class. This class encapsulates a collection of namespaces and provides a variety of namespace management tasks, such as resolving, adding, and removing namespaces to a collection, and providing scope management for the namespaces.

First, the sample creates an XmlDocument and loads the orders.xml file into the XmlDocument. XmlDocument myXmlDocument = new XmlDocument(); myXmlDocument.Load(args); Dim myXmlDocument As XmlDocument = New XmlDocument() myXmlDocument.Load(args) XmlDocument* myXmlDocument = new XmlDocument(); myXmlDocument->Load(args);

To get all the item elements for the yourns1 namespace, the samples uses the following XPath expression: //yourns1:item. The sample also creates an XmlNamespaceManager that contains the prefixes and namespaces in the XML document.

The orders.xml document defines two prefixes: myns for http://tempuri.org/myUSorderprocessornamespace and yourns1 for http://tempuri.org/USvendor1namespace. The document also has the default namespace of http://tempuri.org/myUSordersnamespace which we will map to the "ns" namespace. The reason for needing a prefix for the default namespace in our XPath query is due to the fact that in XPath, there is no concept of a default namespace. Instead elements and attributes that have a namespace require a prefix for matching while unprefixed names in queries can only be used for elements or that do not have a namespace (i.e. are in the null namespace). exprString = String.Format("// {0}:item", "yourns1"); // Create an XmlNamespaceManager and add the namespaces for the document. XmlNamespaceManager nsmanager = new XmlNamespaceManager(myXmlDocument.NameTable); // Map namespaces to prefixes for querying purposes. nsmanager.AddNamespace("defaultns", "http://tempuri.org/myUSordersnamespace"); nsmanager.AddNamespace("myns", "http://tempuri.org/myUSorderprocessornamespace"); nsmanager.AddNamespace("yourns1", "http://tempuri.org/USvendor1namespace"); nsmanager.AddNamespace("yourns2", "http://tempuri.org/USvendor2namespace"); exprString = String.Format("//{0}:item", "yourns1") 'Create an XmlNamespaceManager and add the namespaces for the document. Dim nsmanager As XmlNamespaceManager = New XmlNamespaceManager(myXmlDocument.NameTable) 'Map namespaces to prefixes for querying purposes. nsmanager.AddNamespace("defaultns", "http://tempuri.org/myUSordersnamespace") nsmanager.AddNamespace("myns", "http://tempuri.org/myUSorderprocessornamespace") nsmanager.AddNamespace("yourns1", "http://tempuri.org/USvendor1namespace") nsmanager.AddNamespace("yourns2", "http://tempuri.org/USvendor2namespace") exprString = String::Format(S"//{0}:item", S"yourns1"); //Create an XmlNamespaceManager and add the namespaces for the document. XmlNamespaceManager* nsmanager = new XmlNamespaceManager(myXmlDocument->NameTable); //Map namespaces to prefixes for querying purposes. nsmanager->AddNamespace(S"defaultns", S"http://tempuri.org/myUSordersnamespace"); nsmanager->AddNamespace(S"myns", S"http://tempuri.org/myUSorderprocessornamespace"); nsmanager->AddNamespace(S"yourns1", S"http://tempuri.org/USvendor1namespace"); nsmanager->AddNamespace(S"yourns2", S"http://tempuri.org/USvendor2namespace");

This sample then calls the SelectNodes method on the XmlDocument. In this case, the SelectNodes method finds all item nodes with a yourns1 prefix that resolves to the namespace, http://tempuri.org/USvendor1namespace.

The SelectNodes method returns an XmlNodeList. The sample then display this node list. XmlNodeList nodelist = myXmlDocument.SelectNodes(exprString, nsmanager); foreach (XmlNode myXmlNode in nodelist) { DisplayTree(myXmlNode); } Dim nodelist As XmlNodeList = myXmlDocument.SelectNodes(exprString, nsmanager) Dim myXmlNode As XmlNode For Each myXmlNode In nodelist DisplayTree(myXmlNode) Next XmlNodeList* nodelist = myXmlDocument->SelectNodes(exprString, nsmanager); for (int i = 0; i < nodelist->Count; i++) { DisplayTree(nodelist->Item(i)); }