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Select Single Node in VB.Net problems

Posted on 2007-03-29
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618 Views
Last Modified: 2008-01-09
Hi,

I'm having problems removing nodes from an XML file in vb.net 2003.  I took my existing functioning VB6 code and altered this to reference the correct objects etc.  However i just keep getting an error;

System.NullReferenceException: Object reference not set to an instance of an object.  I am using the wrong object for oRefNode  & oNode?

This is driving me mad an any ideas would be gratefully appreciated.
Thanks,
G

CODE BELOW
---------------------------------------------------------------------------------------------------

Dim mdocNewXmlDoc2 As XmlDocument
Dim oRefNode As XmlNode
Dim oNode As XmlNode

mdocNewXmlDoc2 = New XmlDocument
        mdocNewXmlDoc2.Load("C:\Projects\CIS\xmlOut.xml")
        oRefNode = mdocNewXmlDoc2.SelectSingleNode("/GovTalkMessage/Body/IRenvelope/IRheader")
        oNode = mdocNewXmlDoc2.SelectSingleNode("/GovTalkMessage/Body/IRenvelope/IRheader/IRmark")
      Try
            If Not oNode.InnerText = vbNull Then
                oRefNode.RemoveChild(oNode)
            End If
      Catch esc As SystemException
            MsgBox("A system error ocurred" & vbNewLine & esc.ToString(), MsgBoxStyle.Critical)
            Console.WriteLine("************************************************")
            Console.WriteLine(esc.ToString())
     End Try
0
Comment
Question by:1114godders
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12 Comments
 
LVL 18

Expert Comment

by:DarrenD
ID: 18816184
The only thing that I do differently is

Dim oNodeRoot, oNode As XmlNode

' Load the root node with the entire document.
oNodeRoot = oXMLDOMDoc.DocumentElement

' Retrieve the required node using xPath.
oNode = oNodeRoot.SelectSingleNode("/Blah.Blah/BlehElement")

Darren
0
 
LVL 18

Expert Comment

by:DarrenD
ID: 18816189
Never mind the . in the path.  Once your path is correct.
0
 

Author Comment

by:1114godders
ID: 18816628
Darren,

many thanks for that, however i am still getting an "System.NullReferenceException: Object reference not set to an instance of an object" on the RemoveChild function, i know i'm not far away from getiting this to work, but it feels like much further at the moment.

And the objectoNode is still null after;
oNode = oRefNode.SelectSingleNode("/GovTalkMessage/Body/IRenvelope/IRheader/IRmark")

mdocNewXmlDoc2 = New XmlDocument
mdocNewXmlDoc2.Load("C:\Projects\CIS\xmlOut.xml")
oRefNode = mdocNewXmlDoc2.DocumentElement
oNode = oRefNode.SelectSingleNode("/GovTalkMessage/Body/IRenvelope/IRheader/IRmark")
        Try
            oRefNode.RemoveChild(oNode)
        Catch esc As SystemException
            MsgBox("A system error ocurred" & vbNewLine & esc.ToString(), MsgBoxStyle.Critical)
            Console.WriteLine(esc.ToString())
        End Try
0
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LVL 18

Expert Comment

by:DarrenD
ID: 18816707
Can you put up you XML file??
0
 

Author Comment

by:1114godders
ID: 18816732
Sure,
<?xml version="1.0" encoding="UTF-8"?>
<GovTalkMessage xmlns="http://www.govtalk.gov.uk/CM/envelope">
  <EnvelopeVersion>2.0</EnvelopeVersion>
  <Header>
    <MessageDetails>
      <Class>IR-CIS-VERIFY</Class>
      <Qualifier>request</Qualifier>
      <Function>submit</Function>
      <CorrelationID/>
      <Transformation>XML</Transformation>
      <GatewayTest>1</GatewayTest>
      <GatewayTimestamp/>
    </MessageDetails>
    <SenderDetails>
      <IDAuthentication>
        <SenderID>CIS161</SenderID>
        <Authentication>
          <Method>clear</Method>
          <Role>principal</Role>
          <Value>testing1</Value>
        </Authentication>
      </IDAuthentication>
    </SenderDetails>
  </Header>
  <GovTalkDetails>
    <Keys>
      <Key Type="TaxOfficeNumber">123</Key>
      <Key Type="TaxOfficeReference">R161</Key>
    </Keys>
    <ChannelRouting>
      <Channel>
        <URI>0772</URI>
        <Product>HRWorks CIS</Product>
      </Channel>
    </ChannelRouting>
  </GovTalkDetails>
  <Body>
    <IRenvelope xmlns="http://www.govtalk.gov.uk/taxation/CISrequest">
      <IRheader>
        <Keys>
          <Key Type="TaxOfficeNumber">123</Key>
          <Key Type="TaxOfficeReference">R161</Key>
        </Keys>
        <PeriodEnd>2008-04-05</PeriodEnd>
        <Principal>
          <Contact>
            <Name>
              <Ttl>Mr</Ttl>
              <Fore>Brian</Fore>
              <Sur>Cooper</Sur>
            </Name>
            <Email Preferred="yes">brian.cooper@wealden.net</Email>
            <Telephone Mobile="no" Preferred="no" Type="work">
              <Number>0208 3647177</Number>
            </Telephone>
            <Fax Mobile="no" Preferred="no" Type="work">
              <Number>0208 3647181</Number>
            </Fax>
          </Contact>
        </Principal>
        <DefaultCurrency>GBP</DefaultCurrency>
        <IRmark Type="generic">                            </IRmark>
        <Sender>Employer</Sender>
      </IRheader>
      <CISrequest>
        <Contractor>
          <UTR>9325648154</UTR>
          <AOref>123PP87654321</AOref>
        </Contractor>
        <Subcontractor>
          <Action>verify</Action>
          <Type>company</Type>
          <TradingName>Plastered</TradingName>
          <WorksRef>ZA001</WorksRef>
          <CRN>NE987654</CRN>
        </Subcontractor>
        <Declaration>yes</Declaration>
      </CISrequest>
    </IRenvelope>
  </Body>
</GovTalkMessage>
0
 
LVL 18

Expert Comment

by:DarrenD
ID: 18817675
Hi,

There is nothing wrong with what you are doing to pull out the nodes.

The problem is with the Namespaces. These seem to be causing a problem. If you take them out it works fine.

I'm don't know off the top of my head how to fix this but there is probably some setting or something.

Sorry I can't be of more help.

Darren

Code:

        Dim mdocNewXmlDoc2 As New XmlDocument
        Dim oRootNode As XmlNode
        Dim oNode As XmlNode


        Try
            mdocNewXmlDoc2.Load("C:\Projects\CIS\xmlOut.xml")

            oRootNode = mdocNewXmlDoc2.DocumentElement()

            oNode = oRootNode.SelectSingleNode("/GovTalkMessage/Body/IRenvelope/IRheader/IRmark")


            If Not oNode Is Nothing Then
                oRootNode.RemoveChild(oNode)
            End If
        Catch esc As SystemException
            MsgBox("A system error ocurred" & vbNewLine & esc.ToString(), MsgBoxStyle.Critical)
            Console.WriteLine("************************************************")
            Console.WriteLine(esc.ToString())
        End Try
0
 

Author Comment

by:1114godders
ID: 18822307
Darren,

Many thanks for that, by the Namespaces do you mean the ones in VB.Net?  If i remove the namespaces won't the code just not run at all, im a bit confused here?

G
0
 
LVL 18

Accepted Solution

by:
DarrenD earned 125 total points
ID: 18822510
Sorry,

What I ment was if you remove the

xmlns="http://www.govtalk.gov.uk/taxation/CISrequest"
and
xmlns="http://www.govtalk.gov.uk/CM/envelope"

from the XML file it works fine so there must be some workaround for this.

I don't know what it is though.

If you take out these lines from the XML your the code will work fine

Cheers,

Darren
0
 

Author Comment

by:1114godders
ID: 18822794
Very strange, will need to think about this one a while, but i'll give you points for at least figuring out why it wasn't working.
0
 
LVL 18

Expert Comment

by:DarrenD
ID: 18823126
I know it's really wierd

Have a look here

http://pluralsight.com/blogs/keith/archive/2005/10/19/15714.aspx
0
 
LVL 18

Expert Comment

by:DarrenD
ID: 18823148
That article shows how to strip out the xmlns using regular expressions further down the post.

Probably better off reading the entire article comments and all.

Darren
0
 
LVL 18

Expert Comment

by:DarrenD
ID: 18823179
Here's another article

http://www.devx.com/DevX/Tip/21337
0

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