How to specify fully qualified element names in XPath queries by using Visual C++ .NET or Visual C++ 2005 (815677)

SUMMARY

The step-by-step article describes how to specify fully-qualified element names in the NamespacePrefix:ElementName format to select nodes in an XmlDocument object.

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Create the XML file

1. Paste the following XML code in Notepad, or a text editor of your choice:

   <?xml version="1.0"?>
      <bk:Books xmlns:bk='http://myserver/myschemas/Books'>
        <bk:Book>
            <bk:Title>Just XML</bk:Title>
        </bk:Book>
        <bk:Book>
            <bk:Title>Professional XML</bk:Title>
        </bk:Book>
        <bk:Book>
            <bk:Title>XML Step by Step</bk:Title>
        </bk:Book>
        <bk:Book>
            <bk:Title>XML By Example</bk:Title>
        </bk:Book>
      </bk:Books>

2. On the File menu, click Save.
3. In the Save As dialog box, click All Files in the Save as type box. In the File name text box, type Books.xml, and then click OK.

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Create the Visual C++ .NET or Visual C++ 2005 project

The following code sample uses the following objects and classes:

• XPathNavigator class: This class is based on the XML Path Language (XPath) data model and provides the methods that you must have to implement XPath queries over any data store.
• XPathExpression class: This class encapsulates a compiled XPath expression and is returned when you call the XPathNavigator.Compile method. The Select, Evaluate, and Matches methods use this class.
• XmlNamespaceManager class: This class resolves, adds, and removes namespaces to a collection. XmlNamespaceManager also provides scope management for these namespaces. Because Books.xml uses the bk namespace in the code to follow, you must use XmlNamespaceManager.
• XPathNodeIterator class: This class provides an iterator over a set of selected nodes.

To create and run the Visual C++ .NET or Visual C++ 2005 project, follow these steps:

1. Create a new Windows Forms Application project in Visual C++ .NET or in Visual C++ 2005. By default, a form that is named Form1 is added to the project.
2. Add a Button control and a TextBox control to Form1.
3. Set the MultiLine property of the TextBox control to True, and then set the Text property of the TextBox control to null.
4. Adjust the size of the TextBox to hold four or five lines of data.
5. On the View menu, click Code to open the Code window. Add the following code to the top of the Code window:

   using namespace System::Xml;
   using namespace System::Xml::XPath;

6. To load the Books.xml file in an XmlDocument object, add the following code to the Click event of the Button control:

   XmlDocument* oxmldoc = new XmlDocument();
   oxmldoc->Load("c:\\Books.xml");

   Note Make sure that the Books.xml path in this code points to the correct path on your computer.
7. 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();

8. 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("//bk:Book[position()>=2]");

9. Use the AddNamespace method to add the bk namespace to the XmlNamespaceManager object:

   XmlNamespaceManager* oxmlNSManager= new XmlNamespaceManager(oXPathNav.NameTable);
   oxmlNSManager->AddNamespace("bk", "http://myserver/myschemas/Books");

10. Use the SetContext method of XPathExpression to set the XPathExpression context to the XmlNamespaceManager:

    Expr->SetContext(oxmlNSManager);

11. To run the XPath query and to return the selected nodes, pass the expression to the Select method of the XPathNodeIterator:

    this->textBox1->Text = System::String::Concat(System::String::Concat(this->textBox1->Text,"\r\n"),iterator->Current->Value);

12. The code in the Button1_Click event should appear as follows:

    try{
    	 XmlDocument* oxmldoc = new XmlDocument();
    	 oxmldoc->Load("c:\\Books.xml");
                     
    	 XPathNavigator* oXPathNav;
    	 oXPathNav = oxmldoc->CreateNavigator();
                     
    	 XPathExpression* Expr;
    	 Expr = oXPathNav->Compile("//bk:Book[position()>=2]");
    	 
    	 XmlNamespaceManager* oxmlNSManager= new XmlNamespaceManager(oXPathNav->NameTable);
    	 oxmlNSManager->AddNamespace("bk", "http://myserver/myschemas/Books");
                         
    	 Expr->SetContext(oxmlNSManager);
                     
    	 XPathNodeIterator* iterator = oXPathNav->Select(Expr);
    	 while (iterator->MoveNext())				
    	 {
    		 this->textBox1->Text = System::String::Concat(System::String::Concat(this->textBox1->Text,"\r\n"),iterator->Current->Value);
    	 }
    	 oxmldoc = NULL;
    	 oXPathNav = NULL;
    	 oxmlNSManager = NULL;					 
    }
    catch (Exception* exc)
    {
    	 MessageBox::Show(exc->Message);
    }

    Note You must add the common language runtime support compiler option (/clr:oldSyntax) in Visual C++ 2005 to successfully compile the previous code sample. To add the common language runtime support compiler option in Visual C++ 2005, follow these steps:
    1. Click Project, and then click <ProjectName> Properties.
       
       Note <ProjectName> is a placeholder for the name of the project.
    2. Expand Configuration Properties, and then click General.
    3. Click to select Common Language Runtime Support, Old Syntax (/clr:oldSyntax) in the Common Language Runtime support project setting in the right pane, click Apply, and then click OK.
    For more information about the common language runtime support compiler option, visit the following Microsoft Web site:

    /clr (Common Language Runtime Compilation)
    http://msdn2.microsoft.com/en-us/library/k8d11d4s.aspx

    These steps apply to the whole article.
13. Press CTRL+SHIFT+S to save all the projects.
14. Press CTRL+SHIFT+B to build the solution.
15. Press CTRL+F5 to run the project.
16. Click Button1. Notice that a list of books whose position is greater than or equal to 2 appears in the text box.

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