如何使用c＃从xml获取子属性

Question

我正在尝试显示xml文件中的数据。我无法获得子元素（类别和单元格）的属性。我收到System.NullReferenceException错误。如何显示子元素？

这是xml的一部分

<group number="3704542" text="3704542" varName="BATCH_NO">
  <category number="1" text="1">
    <dimension axis="column" text="Variables">
      <category label="Batch Run" text="Batch Run" varName="BATCH_RUN_ID" variable="true">
        <cell number="4202" text="4202" varName="BATCH_RUN_ID"/>
      </category>
      <category label="Application" text="Application" varName="APP_ID" variable="true">
        <cell label="Calibration" number="101" text="Calibration" varName="APP_ID"/>
      </category>
  </dimension>
  </category>
</group>

这是c＃代码

private void GetXMLData1()
{
    try
    {
        XNamespace ns = "http://www.ibm.com/software/analytics/spss/xml/oms";
        XDocument testXML = XDocument.Load(@"C:\Users\byilmaz\Desktop\SPSS_SITE\test.xml");

        var cats = from cat in testXML.Descendants(ns + "dimension").Where
                   (cat => (string)cat.Attribute("axis") == "column" && (string)cat.Attribute("text") == "Variables")

                   select new
                       {
                           groupName = cat.Parent.Parent.Attribute("number").Value,
                           catId = cat.Parent.Attribute("number").Value,
                           //catName = cat.Element("category").Attribute("label").Value,
                       };

        foreach (var cat in cats)
        {
            xmlTitle.Text += "Group Name: " + cat.groupName + " and Cat Id: " + cat.catId + "</br>";
            //xmlTitle.Text += "Cat Name: " + cat.catName + " </br>";
        }

    }
    catch (Exception err)
    {
        throw (err);
    }
}

，输出为：

当我从下面的代码中取消注释行时，我收到System.NullReferenceException错误。

//catName = cat.Element("category").Attribute("label").Value,