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Examples

Reading an XML file

' Input parameter file contains the path to the file to read.
' Output parameter doc is an XmlDoc variable that receives the
' parsed XML document that is generated.
 
Public Sub XmlReadFile(ByVal file As String, ByRef doc As XmlDoc)
    Dim exc As Exception
    doc = XmlDoc.LoadFile(file)
    If (doc.ErrorCode <> 0) Then
        Console.Writeline("Input error " & CStr(doc.ErrorCode) _
                           &  ", " & doc.Message)
        exc = New Exception
        exc.ErrorCode = doc.ErrorCode
        Throw exc
    End If
End Sub 

Writing an XML file

' Input parameter file contains the path to the file to write.
' Input parameter doc is an XmlDoc object that contains the
' document tree that is converted.
 
Public Sub XmlWriteFile(ByVal file As String, ByVal doc As XmlDoc)
    Dim exc As Exception
    Try
        doc.SaveFile(file)
    Catch exc
        If doc.ErrorCode <> 0 Then
            Console.Writeline("Output error " & _
                               CStr(doc.ErrorCode) & _
                               ", " & doc.Message)
        End If
        Throw exc
    End Try
End Sub

Accessing data in an XML document tree

Assume we have an XML document tree that was generated from the following XML text:

<?xml version="1.0"?>
<procedureControl cellId="TestCell">
  <command>start</command>
  <procedure jobId="090507001" name="INS">
    <type>protocol</type>
    <testSet>INS_#_090507001</testSet>
    <index>0</index>
  </procedure>
</procedureControl> 

The program below analyzes and displays part of the data contained in the tree.

Public Sub XmlParse(ByVal doc As XmlDoc)
    Dim root As XmlNode
    Dim command As XmlNode
    Dim procedure As XmlNode
    Dim attr As XmlNode
    Dim ss As String
    root = doc.DocumentElement
    command = root.GetElementNode("command")
    procedure = root.GetElementNode("procedure")
    ss = root.GetAttribute("cellId")
    Console.Writeline("cellId = " & ss)
    ss = command.Value
    Console.Writeline("command = " & ss)
    ss = procedure.GetAttribute("jobId")
    Console.Writeline("jobId = " & ss)
    ss = procedure.GetElement("type")
    Console.Writeline("type = " & ss)
    ss = procedure.GetElement("testSet")
    Console.Writeline("typeSet = " & ss)
End Sub

The output produced is:

cellId = TestCell
command = start
jobId = 090507001
type = protocol
typeSet = INS_#_090507001

Searching for an element in the document

If you do not know the structure of a document, you can search for an element by recursively searching through the tree until you find a match. This method is much slower than looking for an element where you expect to find it.

Public Sub XmlSearchTree(ByVal node As XmlNode, _
                         ByVal name As String, _
                         ByRef found As XmlNode)
    Dim child As XmlNode
    found = Nothing
    If node.Name = name Then
        If node.Type = "element" Then
            Console.Writeline("Found " & name)
            found = node
            Return
        End If
    End If
    child = node.FirstChild
    While Not child Is Nothing
        XmlSearchTree(child, name, found) 'recursive call
        If Not found Is Nothing Then
            Return
        End If
        child = child.NextSibling
    End While
End Sub

Creating an XML document from a GPL program

The following program demonstrates how to create the XML document tree that corresponds to the XML text shown above in the third example. If this document is output using the XmlWriteFile program, the resulting XML text will be identical in content to the example except for indentation and line breaks.

Public Sub XmlCreate(ByRef doc As XmlDoc)
    Dim root As XmlNode
    Dim elem As XmlNode
    doc = New XmlDoc("procedureControl")
    root = doc.DocumentElement
    root.AddAttribute("cellId", "TestCell")
    root.AddElement("command", "start")
    elem = root.AddElementNode("procedure")
    elem.AddAttribute("jobId", "090507001")
    elem.AddAttribute("name", "INS")
    elem.AddElement("type", "protocol")
    elem.AddElement("testSet", "INS_#_090507001")
    elem.AddElement("index", "0")
End Sub