Question

I am having trouble with XMLTextWriter.WriteStartElement throwing an exception:

System.InvalidOperationException

when trying to write the second element in my XML document.
This error comes back as “The Writer is closed”. I have not closed it, so I am guessing it has fallen out of scope??
I have created a class to write an XML file using XMLTextWriter as an object within my class. Below is the relevant code. I have found one other post on codeguru that was never answered with the exact same issue. Any ideas for workarounds or otherwise would be appreciated.

Function CreateXML()... 
Try
            _listDocument = New XmlTextWriter(_xmlDI.FullName & "\\" & currentFilename, Nothing)
            CreateHeader()
            AddTimeDateNode()
            CreateXML = True
        Catch xmlErr As XmlException
            MsgBox("Unable to create temporary file(" & currentFilename & ") that is used to change your whitelist or blacklist. " & _
                   "More technical information: " & xmlErr.Message, MsgBoxStyle.Critical, "Can't Continue")
        End Try 
    End Function

Function AddListMember(ByVal listType As String, ByVal listItem As String, ByVal action As String) As Boolean
    _listDocument.WriteStartElement(listItem)  <-- CODE THROWS EXCEPTION HERE!
    _listDocument.WriteAttributeString("listType", listType)
    _listDocument.WriteAttributeString("action", action)
    _listDocument.WriteString(listItem)
    _listDocument.WriteEndElement()
    _listDocument.WriteWhitespace(Chr(13) & Chr(10) & "\t")
    Return True 
End Function

'Sets the XML header
Private Function CreateHeader() As Boolean
    _listDocument.WriteStartDocument(False)
    _listDocument.WriteWhitespace(Chr(13) & Chr(10))
    Return True
End Function

'Add Time Date node
Private Function AddTimeDateNode() As Boolean
    _listDocument.WriteStartElement("DateTimeAdded")
    _listDocument.WriteString(DateTime.Now.ToString)
    _listDocument.WriteEndElement()
    _listDocument.WriteWhitespace(Chr(13) & Chr(10))
    Return True
End Function

I am calling these functions after instantiating a dimension from ListXML (the name of my class) with the following code:

Dim xmloutput As New ListXML

xmloutput.CreateXML()
xmloutput.AddListMember(xmloutput.ReturnWhiteList, currentItem.SenderEmailAddress, xmloutput.ReturnAddAction)

Answer 1

As far as I can tell, it looks like you’re trying to create more than one root element – one for DateTimeAdded and one for your list member.

If you call WriteStartElement in CreateXml() you’d end up with valid XML. You’ll need to end that element before you end the document of course.

(And yes, the codeguru post looks like it’s trying to do the same thing.)

Basically, this is a valid XML document:

<RootElement>
  <FirstElement>
    Content
  </FirstElement>
  <SecondElement>
    Content
  </SecondElement>
</RootElement>

But this is not:

<FirstElement>
  Content
</FirstElement>
<SecondElement>
  Content
</SecondElement>

You were trying to do the latter, hence the problem.