Applied XML Programming for Microsoft .NET.pdf - Csbdu.in

End ClassByVal type As XmlNodeType)After the two classes have been compiled into an assembly, a client SAX applicationcan simply reference and instantiate the parser and the content handler class. Theworld's simplest content handler class is shown here:Public Class MyContentHandlerInherits SaxContentHandlerPublic Overrides Sub Process(_ByVal name As String, _ByVal value As String, _ByVal type As XmlNodeType)If type = XmlNodeType.Element ThenMsgBox(name)End IfEnd SubEnd ClassThe SAX application initializes the parser as follows:Dim saxParser As New SaxParser()Dim myHandler As New MyContentHandler()saxParser.ContentHandler = myHandlersaxParser.Parse(file)Of course, the parser discussed here is fairly minimal, but the design guidelines areconcrete and effective. As an aside, consider the fact that in the client application, thecontent handler class and the form are different classes, which makes updating theuser interface from the content handler class a bit complicated.NoteThe full source code discussed here is provided in this book'ssample files. The application is named SaxParser.Parsing XML FragmentsThe XmlTextReader class provides the basic set of functionalities to process any XMLdata coming from a disk file, a stream, or a URL. This kind of reader works sequentially,reading one node after the next, and does not deliberately provide any ad hoc searchfunction to parse only a particular subtree.In the .NET Framework, to process only fragments of XML data, excerpted from avariety of sources, you can take one of two routes. You can initialize the text readerwith the XML string that represents the fragment, or you can use another, morespecific, reader class—the XmlNodeReader class.The XmlNodeReader class works on the subtree rooted in the XmlNode object passedto the class constructor. A living instance of an XmlNode object is not something youcan obtain through a text reader, however. Only the .NET XML DOM parser can createand return an XmlNode object. We'll examine the details of the XmlNodeReader classin Chapter 5, along with the .NET XML DOM parser.41