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

 1 Imports System.IO
 2 Imports System.Xml
 3 Module ParsingUsingXmlTextReader
 4 Sub Main()
 5   Dim m_xmlr As XmlTextReader
 6   'Create the XML Reader
 7   m_xmlr = New XmlTextReader("C:\Personal\family.xml")
 8   'Disable whitespace so that you don't have to read over whitespaces
 9   m_xmlr.WhiteSpaceHandling = WhiteSpaceHandling.NONE
10   'read the xml declaration and advance to family tag
11   m_xmlr.Read()
12   'read the family tag
13   m_xmlr.Read()
14   'Load the Loop
15   While Not m_xmlr.EOF
16     'Go to the name tag
17     m_xmlr.Read()
18     'if not start element exit while loop
19     If Not m_xmlr.IsStartElement() Then
20       Exit While
21     End If
22     'Get the Gender Attribute Value
23     Dim genderAttribute = m_xmlr.GetAttribute("gender")
24     'Read elements firstname and lastname
25     m_xmlr.Read()
26     'Get the firstName Element Value
27     Dim firstNameValue = m_xmlr.ReadElementString("firstname")
28     'Get the lastName Element Value
29     Dim lastNameValue = m_xmlr.ReadElementString("lastname")
30     'Write Result to the Console
31     Console.WriteLine("Gender: " & genderAttribute _
32       & " FirstName: " & firstNameValue & " LastName: " _
33       & lastNameValue)
34     Console.Write(vbCrLf)
35   End While
36   'close the reader
37   m_xmlr.Close()
38 End Sub
39 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

 1 Imports System.IO
 2 Imports System.Xml
 3 Module ParsingUsingXmlDocument
 4 Sub Main()
 5   Try
 6     Dim m_xmld As XmlDocument
 7     Dim m_nodelist As XmlNodeList
 8     Dim m_node As XmlNode
 9     'Create the XML Document
10     m_xmld = New XmlDocument()
11     'Load the Xml file
12     m_xmld.Load("C:\CMS\Personal\family.xml")
13     'Get the list of name nodes 
14     m_nodelist = m_xmld.SelectNodes("/family/name")
15     'Loop through the nodes
16     For Each m_node In m_nodelist
17       'Get the Gender Attribute Value
18       Dim genderAttribute = m_node.Attributes.GetNamedItem("gender").Value
19       'Get the firstName Element Value
20       Dim firstNameValue = m_node.ChildNodes.Item(0).InnerText
21       'Get the lastName Element Value
22       Dim lastNameValue = m_node.ChildNodes.Item(1).InnerText
23       'Write Result to the Console
24       Console.Write("Gender: " & genderAttribute _
25         & " FirstName: " & firstNameValue & " LastName: " _
26         & lastNameValue)
27       Console.Write(vbCrLf)
28     Next
29   Catch errorVariable As Exception
30     'Error trapping
31     Console.Write(errorVariable.ToString())
32   End Try
33 End Sub
34 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