[vb.net]XML File Parsing in VB.NET

Introduction

Parsing XML files has always been time consuming and sometimes tricky. .NET framework provides powerful new ways of parsing XML. The various techniques know to parse xml files with .NET framework are using XmlTextReader, XmlDocument, XmlSerializer, DataSet and XpathDocument. I will explore the XmlTextReader and XmlDocument approach here.

The Xml File

Figure 1 outlines the xml file that will be parsed.

<?xml version="1.0" encoding="UTF-8"?>
<family>
  <name gender="Male">
    <firstname>Tom</firstname>
    <lastname>Smith</lastname>
  </name>
  <name gender="Female">
    <firstname>Dale</firstname>
    <lastname>Smith</lastname>
  </name>
</family>

Parsing XML with XMLTextReader

Using XmlTextReader is appropriate when the structure of the XML file is relatively simple. Parsing with XmlTextReader gives you a pre .net feel as you sequentially walk through the file using Read() and get data using GetAttribute() andReadElementString() methods. Thus while using XmlTextReader it is up to the developer to keep track where he is in the Xml file and Read() correctly. Figure 2 below outlines parsing of xml file with XmlTextReader

 Imports System.IO
 Imports System.Xml
 Module ParsingUsingXmlTextReader
 Sub Main()
   Dim m_xmlr As XmlTextReader
   'Create the XML Reader
   m_xmlr = New XmlTextReader("C:\Personal\family.xml")
   'Disable whitespace so that you don't have to read over whitespaces
   m_xmlr.WhiteSpaceHandling = WhiteSpaceHandling.NONE
   'read the xml declaration and advance to family tag
   m_xmlr.Read()
   'read the family tag
   m_xmlr.Read()
   'Load the Loop
   While Not m_xmlr.EOF
     'Go to the name tag
     m_xmlr.Read()
     'if not start element exit while loop
     If Not m_xmlr.IsStartElement() Then
       Exit While
     End If
     'Get the Gender Attribute Value
     Dim genderAttribute = m_xmlr.GetAttribute("gender")
     'Read elements firstname and lastname
     m_xmlr.Read()
     'Get the firstName Element Value
     Dim firstNameValue = m_xmlr.ReadElementString("firstname")
     'Get the lastName Element Value
     Dim lastNameValue = m_xmlr.ReadElementString("lastname")
     'Write Result to the Console
     Console.WriteLine("Gender: " & genderAttribute _
       & " FirstName: " & firstNameValue & " LastName: " _
       & lastNameValue)
     Console.Write(vbCrLf)
   End While
   'close the reader
   m_xmlr.Close()
 End Sub
 End Module

Parsing XML with XmlDocument

The XmlDocument class is modeled based on Document Object Model. XmlDocument class is appropriate if you need to extract data in a non-sequential manner. Figure 3 below outlines parsing of xml file with XmlDocument

 Imports System.IO
 Imports System.Xml
 Module ParsingUsingXmlDocument
 Sub Main()
   Try
     Dim m_xmld As XmlDocument
     Dim m_nodelist As XmlNodeList
     Dim m_node As XmlNode
     'Create the XML Document
     m_xmld = New XmlDocument()
     'Load the Xml file
     m_xmld.Load("C:\CMS\Personal\family.xml")
     'Get the list of name nodes
     m_nodelist = m_xmld.SelectNodes("/family/name")
     'Loop through the nodes
     For Each m_node In m_nodelist
       'Get the Gender Attribute Value
       Dim genderAttribute = m_node.Attributes.GetNamedItem("gender").Value
       'Get the firstName Element Value
       Dim firstNameValue = m_node.ChildNodes.Item().InnerText
       'Get the lastName Element Value
       Dim lastNameValue = m_node.ChildNodes.Item().InnerText
       'Write Result to the Console
       Console.Write("Gender: " & genderAttribute _
         & " FirstName: " & firstNameValue & " LastName: " _
         & lastNameValue)
       Console.Write(vbCrLf)
     Next
   Catch errorVariable As Exception
     'Error trapping
     Console.Write(errorVariable.ToString())
   End Try
 End Sub
 End Module

You will see the following result for both

Gender: Male FirstName: Tom LastName: Smith

Gender: Female FirstName: Dale LastName: Smith

http://www.codeproject.com/Articles/4826/XML-File-Parsing-in-VB-NET