Parsing XML file in VB.NET using DOM

• Download source code - 15.2 KB

Introduction

There are many versions of XML parsers/readers on the Internet and on CodeProject (including my own in C/C++). This one was written several years ago in VB 6.0 and is based on DOM (Document Object Model). I almost forgot about it until I recently decided to upgrade (or to see if it is possible without much hassle) VB 6.0 projects to VB 2008 (VB 2010 does not recognize VB 6.0 project’s files). I already had a very time consuming experience upgrading a project with many drawing and database related functions and arrays, because it requires you to manually rewrite the old code.
XML parser does not have any drawing functions or VB6-arrays and was upgraded to VB.NET automatically, though generating warnings related mostly to default property of the object. I removed these lines from code but for anyone interested, I left the _UpgradeReport.htm in the project.

Using the Code

XML file provided with the code sample is stocks.xml file from MSXML 4.0 SDK:

Though VB 6.0 and VB.NET are different languages, they still have very much in common and for the fairness of this experimental upgrade, I didn’t change and didn’t correct anything in the code. Thus, for example, you can see old style error handling instead of Try-Catch blocks.

'---1.Load an xml document into a DOM instance----------------
  oXMLDom.async = False
  oXMLDom.validateOnParse = False
  oXMLDom.resolveExternals = False
  oXMLDom.preserveWhiteSpace = True
  fileName = txtFileName.Text

  If oXMLDom.load(My.Application.Info.DirectoryPath & "\" & fileName) = False Then

   ErrorMessage = "Error message: failed to load XML data from file." _
            & vbCrLf & "Check the file name."

   Response = MsgBox(ErrorMessage, StyleWarning)
   'MsgBox "Error: failed to load XML data from file. Check the file name."
  End If

  '-----2.Get the root node and print its name---------------------
  'get root element:
  root = oXMLDom.documentElement
  'output the name of root node

  strout = "Root node: " & root.nodeName & vbCrLf & vbCrLf

  txtOutput.Text = strout
  '----------------
  'Create an IXMLDOMNodeList object by using the xml document's
  'getElementsByTagName method, and examine the content of each node.

  '------3.Output the elements with values, parent nodes and attributes---------------
  'output "Items" nodes:
  objNodeList = oXMLDom.getElementsByTagName(" ")
  'strout = "The node list has " & objNodeList.length & " items." & vbCrLf
  Dim Attrib As Object
  '"objNodeList" index starts from 0:
  For i = 1 To (objNodeList.length)

   'Output only elements:

   If objNodeList.item(i - 1).nodeType = MSXML2.tagDOMNodeType.NODE_ELEMENT Then
    n = n + 1 'element node's counter

    '"item" index starts from 0
       strout = strout & vbCrLf & CStr(n) & vbCrLf & "Type: " _
    & objNodeList.item(i - 1).nodeTypeString & vbCrLf & "Node: " _
           & objNodeList.item(i - 1).nodeName & vbCrLf & "Text: " _
    & objNodeList.item(i).text & vbCrLf & "Parent node: " _
           & objNodeList.item(i - 1).parentNode.nodeName & vbCrLf _
    & "Child nodes: " & objNodeList.item(i - 1).childNodes.length _
           & vbCrLf & vbCrLf

    For Each Attrib In objNodeList.item(i - 1).attributes

     strout = strout & "Attribute type: " & Attrib.nodeTypeString & _
    vbCrLf & "Attribute name: " _
         & Attrib.Name & vbCrLf & "Value: " & Attrib.nodeValue & vbCrLf
    Next Attrib

   End If
  Next  

This is the output of the parsing:

Note that to run the executable, you have to place the generated Interop.MSXML2.dll file in .exe file's directory.

References

• MSXML 4.0 SDK
• W3C, DOM

History

• 08.2009 - Built in Visual Basic 6.0
• 12.06.2011 - Recompiled in Visual Basic 2008