How do I check if section and subdivision exist inside object's xml?

[okaymy1112]

My function is working but not as I expect it to. The problem is that when Section and Subvision are not found in the object aobjXmlGetStatuteRequestNode xml, I get an error NullReference Exception was unhandled by user code. Object reference not set to an instance of an object.
For that reason, because the two elements are optional, I would like to check if they exist before adding their value into the xml inside the object objXmlRequestMessageDoc.
The if statement I used in my function did not work. When it found Section element, it did not check for Subdivision. How do I check for both and add them if they exist. If they do not exist, I do not need to do anything and should not throw an error since they are optional.​

Object aobjXmlGetStatuteRequestNode has this xml

<ns:GetStatutesRequest xmlns:ns="http://www.courts.state.mn.us/StatuteService/1.0">
<ns:Statute>
    <ns:Chapter>169</ns:Chapter>
            <!--Optional:-->
    <ns:Section>191</ns:Section>
            <!--Optional:-->
    <ns:Subdivision>a</ns:Subdivision>
</ns:Statute>

The following output in the objXmlRequestMessageDoc object sis correct but this does not work when Section and or Subdivision are not found in the object aobjXmlGetStatuteRequestNode.

<ns:BasicSearchQueryRequest xmlns:ns="http://crimnet.state.mn.us/mnjustice/statute/service/4.0">
    <ns1:BasicSearchCriteria xmlns:ns1="http://crimnet.state.mn.us/mnjustice/statute/messages/4.0">
        <ns2:Chapter xmlns:ns2="http://crimnet.state.mn.us/mnjustice/statute/4.0"/169</ns2:Chapter>>
        <ns2:Section xmlns:ns2="http://crimnet.state.mn.us/mnjustice/statute/4.0"/>191</ns2:Chapter>
        <ns2:Subdivision xmlns:ns2="http://crimnet.state.mn.us/mnjustice/statute/4.0"/>a</ns2:Chapter>
    </ns1:BasicSearchCriteria>
</ns:BasicSearchQueryRequest>

Here is my function

 Function GetStatutesByChapter(ByVal aobjXmlGetStatuteRequestNode As XmlNode, ByVal aobjXMLNameSpaceManager As XmlNamespaceManager, ByVal aobjBroker As ServiceCatalog.Library.v4.Broker) As XmlDocument
            Dim objXmlRequestMessageDoc As XmlDocument
            Dim objXmlResponseMessageDoc As XmlDocument
            Dim intCount As Integer
            aobjBroker.PostMessageWarehouseInformationalMessage("Chapter found.", 1)
            objXmlResponseMessageDoc = New XmlDocument
            'Add the first element into the document GetStatuteByChapter with its namespace
            objXmlResponseMessageDoc.AppendChild(objXmlResponseMessageDoc.CreateElement("BasicSearchQueryResponse", "[URL]http://crimnet.state.mn.us/mnjustice/statute/service/4.0[/URL]"))
         'Create the BCA request message
            objXmlRequestMessageDoc = New XmlDocument
            objXmlRequestMessageDoc.AppendChild(objXmlRequestMessageDoc.CreateElement("ns:BasicSearchQueryRequest", aobjXMLNameSpaceManager.LookupNamespace("ns")))
            objXmlRequestMessageDoc.SelectSingleNode("ns:BasicSearchQueryRequest", aobjXMLNameSpaceManager).AppendChild(objXmlRequestMessageDoc.CreateElement("ns1:BasicSearchCriteria", aobjXMLNameSpaceManager.LookupNamespace("ns1")))
            objXmlRequestMessageDoc.SelectSingleNode("ns:BasicSearchQueryRequest/ns1:BasicSearchCriteria", aobjXMLNameSpaceManager).AppendChild(objXmlRequestMessageDoc.CreateElement("ns2:Chapter", aobjXMLNameSpaceManager.LookupNamespace("st")))
            objXmlRequestMessageDoc.SelectSingleNode("ns:BasicSearchQueryRequest/ns1:BasicSearchCriteria", aobjXMLNameSpaceManager).AppendChild(objXmlRequestMessageDoc.CreateElement("ns2:Section", aobjXMLNameSpaceManager.LookupNamespace("st")))
            objXmlRequestMessageDoc.SelectSingleNode("ns:BasicSearchQueryRequest/ns1:BasicSearchCriteria", aobjXMLNameSpaceManager).AppendChild(objXmlRequestMessageDoc.CreateElement("ns2:Subdivision", aobjXMLNameSpaceManager.LookupNamespace("st")))
            objXmlRequestMessageDoc.DocumentElement.SelectSingleNode("ns1:BasicSearchCriteria/st:Chapter", aobjXMLNameSpaceManager).InnerText = aobjXmlGetStatuteRequestNode.SelectSingleNode("ss:Statute/ss:Chapter", aobjXMLNameSpaceManager).InnerText
            objXmlRequestMessageDoc.DocumentElement.SelectSingleNode("ns1:BasicSearchCriteria/st:Section", aobjXMLNameSpaceManager).InnerText = aobjXmlGetStatuteRequestNode.SelectSingleNode("ss:Statute/ss:Section", aobjXMLNameSpaceManager).InnerText
            objXmlRequestMessageDoc.DocumentElement.SelectSingleNode("ns1:BasicSearchCriteria/st:Subdivision", aobjXMLNameSpaceManager).InnerText = aobjXmlGetStatuteRequestNode.SelectSingleNode("ss:Statute/ss:Subdivision", aobjXMLNameSpaceManager).InnerText
            'check if there is a section and or subdivision if it is there then set the value
            'If Not (aobjXmlGetStatuteRequestNode.SelectSingleNode("ss:Statute/ss:Section", aobjXMLNameSpaceManager).InnerText) Is Nothing Then
            '    objXmlRequestMessageDoc.DocumentElement.SelectSingleNode("ns1:BasicSearchCriteria/st:Section", aobjXMLNameSpaceManager).InnerText = aobjXmlGetStatuteRequestNode.SelectSingleNode("ss:Statute/ss:Section", aobjXMLNameSpaceManager).InnerText
            'End If
            'check if there is a section and or subdivision if it is there then set the value
            aobjBroker.PostMessageWarehouseSnapshot(objXmlRequestMessageDoc.OuterXml, "Request Message", 1)
            'Call the BCA service
            intCount = 0
            'Count how many Statute node found
            CType(objXmlResponseMessageDoc.SelectSingleNode("ss:GetStatutesResponse/ss:StatutesXml/ss:Statutes", aobjXMLNameSpaceManager), System.Xml.XmlElement).SetAttribute("totalCount", CStr(intCount))
            Return objXmlResponseMessageDoc
        End Function

 

[JohnH]

XmlNode.SelectSingleNode Method (String, XmlNamespaceManager) (System.Xml)

Return Value
Type: System.Xml.XmlNode
The first XmlNode that matches the XPath query or null if no matching node is found.

That means you first have to assign result of SelectSingleNode function call in a variable, check if variable is Nothing, and if not you can continue to work with the object reference.