Microsoft KB Archive/313188

= How To Specify Fully Qualified Element Names in XPath Queries by Using Visual C# .NET =

Article ID: 313188

Article Last Modified on 1/13/2006

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APPLIES TO


 * Microsoft Visual C# .NET 2002 Standard Edition
 * Microsoft Visual C# .NET 2003 Standard Edition
 * Microsoft .NET Framework 1.0
 * Microsoft .NET Framework 1.1

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This article was previously published under Q313188



For a Microsoft Visual Basic .NET version of this article, see 308062.

This article refers to the following Microsoft .NET Framework Class Library namespaces:
 * System.Xml
 * System.Xml.XPath

IN THIS TASK

 * SUMMARY
 * Create the XML File
 * Create the Visual C# .NET Project
 * REFERENCES



SUMMARY
The step-by-step article shows you how to specify fully qualified element names in the  format to select nodes in an XmlDocument object.

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Create the XML File
 On the Windows Start menu, point to Run, type notepad.exe, and then click OK to open Notepad.  Copy and paste the following XML code into Notepad:    Just XML   Professional XML </bk:Book>  XML Step by Step</bk:Title> </bk:Book>  XML By Example</bk:Title> </bk:Book> </bk:Books> </li> On the File menu, click Save.</li> In the Save As dialog box, in the Save as type text box, click All Files. In the File name text box, type Books.xml, and then click OK.</li></ol>

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Create the Visual C# .NET Project
The following code sample uses the following objects and classes:
 * The XPathNavigator class: XPathNavigator is based on the XML Path Language (XPath) data model and provides the methods that are required to implement XPath queries over any data store.
 * The XPathExpression class: This class encapsulates a compiled XPath expression and is returned when you call Compile. The Select, Evaluate, and Matches methods use this class.
 * The XmlNamespaceManager class: XmlNamespaceManager resolves, adds, and removes namespaces to a collection. XmlNamespaceManager also provides scope management for these namespaces. Because Books.xml uses the &quot;bk&quot; namespace in the code to follow, you must use XmlNamespaceManager.
 * The XPathNodeIterator class: This object provides an iterator over a set of selected nodes.

To create and run the Visual C# .NET project, follow these steps: <ol> Create a new Windows Application project in Visual C# .NET. Form1 is added to the project by default.</li> Place a Button control and a TextBox control on Form1.</li> Set the MultiLine property of the TextBox control to True.</li> Click to expand the TextBox control so that you can view four or five lines of data.</li>  Add the following code to the top of the Code window: using System.Xml; using System.Xml.XPath; </li>  To load the Books.xml file into an XmlDocument object, add the following code to the Click event of the Button control: XmlDocument oxmldoc = new XmlDocument; oxmldoc.Load(@&quot;c:\Books.xml&quot;); </li> Make sure that the Books.xml path in the preceding code points to the correct path on your computer.</li>  Use the CreateNavigator method of the XmlDocument object to create the XPathNavigator object so that you can run the XPath query: XPathNavigator oXPathNav; oXPathNav = oxmldoc.CreateNavigator; </li>  Use the Compile method of XPathNavigator to create an XPathExpression class, and then pass the XPath query as the parameter: XPathExpression Expr; Expr = oXPathNav.Compile(&quot;//bk:Book[position>=2]&quot;); </li>  Use the the AddNamespace method to add the &quot;bk&quot; namespace to the XmlNamespaceManager object: XmlNamespaceManager oxmlNSManager = new XmlNamespaceManager(oXPathNav.NameTable); oxmlNSManager.AddNamespace(&quot;bk&quot;, &quot;http://myserver/myschemas/Books&quot;); </li> <li> Use the SetContext method of XPathExpression to set the XPathExpression context to the XmlNamespaceManager: Expr.SetContext(oxmlNSManager); </li> <li> To run the XPath query and return the selected nodes, pass the expression to the Select method of the XPathNodeIterator: XPathNodeIterator iterator = oXPathNav.Select(Expr); while (iterator.MoveNext) {   this.textBox1.Text = this.textBox1.Text + &quot;\r\n&quot;+ iterator.Current.Value ; }                   </li> <li> The code in Button1_Click event should appear as follows: XmlDocument oxmldoc = new XmlDocument; try { oxmldoc.Load(&quot;c:\\Books.xml&quot;);

XPathNavigator oXPathNav; oXPathNav = oxmldoc.CreateNavigator;

XPathExpression Expr; Expr = oXPathNav.Compile(&quot;//bk:Book[position>=2]&quot;);

XmlNamespaceManager oxmlNSManager = new XmlNamespaceManager(oXPathNav.NameTable); oxmlNSManager.AddNamespace(&quot;bk&quot;, &quot;http://myserver/myschemas/Books&quot;); Expr.SetContext(oxmlNSManager);

XPathNodeIterator iterator = oXPathNav.Select(Expr); while (iterator.MoveNext) {   this.textBox1.Text = this.textBox1.Text + &quot;\r\n&quot;+ iterator.Current.Value ; } oxmlNSManager = null; oXPathNav = null; oxmldoc = null; } catch (Exception exc) {       MessageBox.Show(exc.Message); }                   </li> <li>Build and run the project.</li> <li>Click Button1. Notice that a list of books whose position is greater than or equal to 2 appears in the textbox.</li></ol>

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