使用Vb.Net如何檢查節/細分是否存在並將其值添加到xml文檔中？

Question

我的功能正在運行，但沒有達到我的預期。 問題是，當在對象aobjXmlGetStatuteRequestNode中未找到Section和Subvision時，出現錯誤NullReference Exception是用戶代碼未處理的。 你調用的對象是空的。

因此，由於這兩個元素是可選的，因此我想在將其值添加到對象objXmlRequestMessageDoc中的xml中之前檢查它們是否存在。

我在函數中使用的if語句不起作用。 當找到Section元素時，它沒有檢查細分。

如何檢查兩者並添加它們（如果存在）。 如果它們不存在，那么我不需要做任何事情，也不要拋出錯誤，因為它們是可選的。 對象aobjXmlGetStatuteRequestNode中包含此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>

objXmlRequestMessageDoc對象中的以下輸出是正確的，但是當在對象aobjXmlGetStatuteRequestNode中找不到Section和或Subdivision時，此輸出將不起作用。

<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>

這是我的功能

 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", "http://crimnet.state.mn.us/mnjustice/statute/service/4.0"))

     '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

Answer 1

我已經通過以下兩個if語句解決了這個問題

'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) Is Nothing) Then
            objXmlRequestMessageDoc.DocumentElement.SelectSingleNode("ns1:BasicSearchCriteria/st:Section", aobjXMLNameSpaceManager).InnerText = aobjXmlGetStatuteRequestNode.SelectSingleNode("ss:Statute/ss:Section", aobjXMLNameSpaceManager).InnerText
        End If

        If Not (aobjXmlGetStatuteRequestNode.SelectSingleNode("ss:Statute/ss:Subdivision", aobjXMLNameSpaceManager) Is Nothing) Then
            objXmlRequestMessageDoc.DocumentElement.SelectSingleNode("ns1:BasicSearchCriteria/st:Subdivision", aobjXMLNameSpaceManager).InnerText = aobjXmlGetStatuteRequestNode.SelectSingleNode("ss:Statute/ss:Subdivision", aobjXMLNameSpaceManager).InnerText
        End If