即使节点具有值，XMLNode也会获取NullReferenceException

Question

当XML节点具有值时，似乎无法弄清楚为什么我得到NullReferenceException。我是否可以正确访问该节点？

当尝试遍历子节点时，我在下面的行上得到一个空引用异常。我希望它很小，我将继续阅读/搜索答案，但我认为询问可能会更快。非常感谢您提供任何帮助，谢谢！

     variable += childNode.SelectSingleNode(".//my:AP1SupportingDelDetailsTextBox", nsManager).InnerText + "\n";

parenttxt / xml

<my:AP1ExpectedMilestones
    xmlns:my="http://schemas.microsoft.com/office/infopath/2003/myXSD/2018-07-23T12:40:33">
    <my:AP1SupportingActionTextBox>Action1</my:AP1SupportingActionTextBox>
    <my:AP1SupportingActionHasDeliverablesCheckBox>true</my:AP1SupportingActionHasDeliverablesCheckBox>
    <my:AP1AssociatedDelSection>
        <my:AP1AssociatedDelRepeatingTable>
            <my:AP1SupportingDelDetailsTextBox>Action1del1</my:AP1SupportingDelDetailsTextBox>
            <my:AP1SupportingDelDatePick>2018-09-28</my:AP1SupportingDelDatePick>
        </my:AP1AssociatedDelRepeatingTable>
        <my:AP1AssociatedDelRepeatingTable>
            <my:AP1SupportingDelDetailsTextBox>Action1del2</my:AP1SupportingDelDetailsTextBox>
            <my:AP1SupportingDelDatePick>2018-09-28</my:AP1SupportingDelDatePick>
        </my:AP1AssociatedDelRepeatingTable>
        <my:AP1AssociatedDelRepeatingTable>
            <my:AP1SupportingDelDetailsTextBox>Action1Del3</my:AP1SupportingDelDetailsTextBox>
            <my:AP1SupportingDelDatePick>2018-09-28</my:AP1SupportingDelDatePick>
        </my:AP1AssociatedDelRepeatingTable>
    </my:AP1AssociatedDelSection>
</my:AP1ExpectedMilestones>
<my:AP1ExpectedMilestones
    xmlns:my="http://schemas.microsoft.com/office/infopath/2003/myXSD/2018-07-23T12:40:33">
    <my:AP1SupportingActionTextBox>Action2</my:AP1SupportingActionTextBox>
    <my:AP1SupportingActionHasDeliverablesCheckBox>true</my:AP1SupportingActionHasDeliverablesCheckBox>
    <my:AP1AssociatedDelSection>
        <my:AP1AssociatedDelRepeatingTable>
            <my:AP1SupportingDelDetailsTextBox>Action2Del1</my:AP1SupportingDelDetailsTextBox>
            <my:AP1SupportingDelDatePick>2018-09-28</my:AP1SupportingDelDatePick>
        </my:AP1AssociatedDelRepeatingTable>
        <my:AP1AssociatedDelRepeatingTable>
            <my:AP1SupportingDelDetailsTextBox>Action2Del2</my:AP1SupportingDelDetailsTextBox>
            <my:AP1SupportingDelDatePick>2018-09-28</my:AP1SupportingDelDatePick>
        </my:AP1AssociatedDelRepeatingTable>
    </my:AP1AssociatedDelSection>
</my:AP1ExpectedMilestones>

childtxt / xml

<my:AP1AssociatedDelRepeatingTable
xmlns:my="http://schemas.microsoft.com/office/infopath/2003/myXSD/2018-07-23T12:40:33">
    <my:AP1SupportingDelDetailsTextBox>Action1del1</my:AP1SupportingDelDetailsTextBox>
    <my:AP1SupportingDelDatePick>2018-09-28</my:AP1SupportingDelDatePick>
</my:AP1AssociatedDelRepeatingTable>
<my:AP1AssociatedDelRepeatingTable
    xmlns:my="http://schemas.microsoft.com/office/infopath/2003/myXSD/2018-07-23T12:40:33">
    <my:AP1SupportingDelDetailsTextBox>Action1del2</my:AP1SupportingDelDetailsTextBox>
    <my:AP1SupportingDelDatePick>2018-09-28</my:AP1SupportingDelDatePick>
</my:AP1AssociatedDelRepeatingTable>
<my:AP1AssociatedDelRepeatingTable
    xmlns:my="http://schemas.microsoft.com/office/infopath/2003/myXSD/2018-07-23T12:40:33">
    <my:AP1SupportingDelDetailsTextBox>Action1Del3</my:AP1SupportingDelDetailsTextBox>
    <my:AP1SupportingDelDatePick>2018-09-28</my:AP1SupportingDelDatePick>
</my:AP1AssociatedDelRepeatingTable>
<my:AP1AssociatedDelRepeatingTable
    xmlns:my="http://schemas.microsoft.com/office/infopath/2003/myXSD/2018-07-23T12:40:33">
    <my:AP1SupportingDelDetailsTextBox>Action2Del1</my:AP1SupportingDelDetailsTextBox>
    <my:AP1SupportingDelDatePick>2018-09-28</my:AP1SupportingDelDatePick>
</my:AP1AssociatedDelRepeatingTable>
<my:AP1AssociatedDelRepeatingTable
    xmlns:my="http://schemas.microsoft.com/office/infopath/2003/myXSD/2018-07-23T12:40:33">
    <my:AP1SupportingDelDetailsTextBox>Action2Del2</my:AP1SupportingDelDetailsTextBox>
    <my:AP1SupportingDelDatePick>2018-09-28</my:AP1SupportingDelDatePick>
</my:AP1AssociatedDelRepeatingTable>

调试代码

  [WebMethod]
        public void showXML(XmlDocument doc)
        {



            // declare namespaces
            XmlNamespaceManager nsManager = new XmlNamespaceManager(doc.NameTable);
            //nsManager.AddNamespace("my", "http://schemas.microsoft.com/office/infopath/2003/myXSD/2018-08-16T17:55:49");
            nsManager.AddNamespace("my", "http://schemas.microsoft.com/office/infopath/2003/myXSD/2018-07-23T12:40:33");
            nsManager.AddNamespace("dfs", "http://schemas.microsoft.com/office/infopath/2003/dataFormSolution");

            // declare the document for parsing
            XmlNode root = doc.DocumentElement;


            // parse the initiatives
            XmlNodeList initiatives = root.SelectNodes("/dfs:IPDocument/my:myFields/my:AP1Main/my:AP1MainRepeatingSection", nsManager);


              foreach (XmlNode node in initiatives)
              {
                // parse the nodes to injest data into the Expected MileStones table
                XmlNodeList expected_milestones = root.SelectNodes(".//my:AP1ExpectedMilestones", nsManager);

                string parenttxt = "" ;
                string childtxt = "";
                string variable = "";

                foreach (XmlNode milestones_node in expected_milestones)
                {
                    parenttxt += milestones_node.OuterXml;


                    string deliverables = milestones_node.SelectSingleNode(".//my:AP1AssociatedDelSection", nsManager);
                    foreach (XmlNode childNode in deliverables.ChildNodes)
                    {

                        childtxt += childNode.OuterXml;

                    variable += childNode.SelectSingleNode(".//my:AP1SupportingDelDetailsTextBox", nsManager).InnerText + "\n";

                    }




                }

                File.WriteAllText(@"C:\Windows\Temp\xml\outputparent.xml", parenttxt);

                File.WriteAllText(@"C:\Windows\Temp\xml\outputchild.xml", childtxt);

                File.WriteAllText(@"C:\Windows\Temp\xml\outputvariable.xml", variable);



            }


        }