xml file parsing in vb

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Rate:Pratik Desai, 21 Aug 2003

XMLFile Parsing in VB.NET

Exploring various methods to parse an XMLfile in a .NET environment

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IntroductionParsing XMLfiles has always been time consuming and sometimes tricky. .NET framework provides powerful

new ways of parsing XML. The various techniques know to parse xmlfiles with .NET framework are

using XmlTextReader,XmlDocument, XmlSerializer, DataSet and XpathDocument. I will explore

theXmlTextReader and XmlDocument approach here.

The XmlFile

Figure 1 outlines the xmlfile that will be parsed.

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Tom Smith Dale Smith

Figure1: Xmlfile

Parsing XMLwith XMLTextReader

Using XmlTextReader is appropriate when the structure of the XMLfile is relatively simple. Parsing

with XmlTextReader gives you a pre .net feel as you sequentially walk through the file using Read() and

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get data usingGetAttribute() andReadElementString() methods. Thus while

usingXmlTextReader it is up to the developer to keep track where he is in the Xmlfile

and Read() correctly. Figure 2 below outlines parsing of xmlfile withXmlTextReader

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Imports System.IOImports System.XmlModule ParsingUsingXmlTextReaderSub Main()

Dim m_xmlr AsXmlTextReader 'Create the XMLReader m_xmlr = NewXmlTextReader("C:\Personal\family.xml") 'Disable whitespace so that you don't have to read over whitespaces

m_xmlr.WhiteSpaceHandling = WhiteSpaceHandling.NONE 'read thexml declaration and advance to family tag m_xmlr.Read() 'read the family tag m_xmlr.Read() 'Load the Loop WhileNot m_xmlr.EOF 'Go to the name tag

m_xmlr.Read()

'if not start element exit while loop IfNot m_xmlr.IsStartElement() Then ExitWhile EndIf '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) EndWhile 'close the reader m_xmlr.Close()EndSubEndModule

Figure 2: XmlParsing with XmlTextReader

Parsing XMLwith XmlDocumentThe XmlDocument class is modeled based on Document Object Model.XmlDocument class is appropriate if

you need to extract data in a nonsequential manner. Figure 3 below outlines parsing of xmlfile

with XmlDocument

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Imports System.IOImports System.XmlModule ParsingUsingXmlDocumentSub Main()


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Try Dim m_xmld AsXmlDocument Dim m_nodelist AsXmlNodeList Dim m_node AsXmlNode 'Create the XML Document m_xmld = NewXmlDocument() 'Load the Xml file m_xmld.Load("C:\CMS\Personal\family.xml")

'Get the list of name nodesm_nodelist = m_xmld.SelectNodes("/family/name")

'Loop through the nodes ForEach 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(0).InnerText 'Get the lastName Element Value

Dim lastNameValue = m_node.ChildNodes.Item(1).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())

EndTryEndSubEndModule

Figure 3: XmlParsing with XmlDocument

Compilation and Result

Make sure you have vbc.exein your path. From the command prompt go

toC:\Personal>. Compile ParsingUsingXmlTextReader.vbandParsingUsingXmlDocument.vb.

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C:\Personal>vbc /out:ParsingUsingXmlTextReadervb.exe ParsingUsingXmlTextReader.vbC:\Personal>vbc /out:ParsingUsingXmlDocumentvb.exe ParsingUsingXmlDocument.vb

When you run the individual program

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C:\Personal>ParsingUsingXmlTextReadervb.exe

OR

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C:\Personal>ParsingUsingXmlDocumentvb.exe

You will see the following result for both

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Gender: Male FirstName: Tom LastName: Smith


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Gender: Female FirstName: Dale LastName: Smith

Conclusion

There are different ways to parse XMLfiles and the best method depends on your situation and the

programming style preferred.

License

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xml file parsing in vb

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