C# 如何从xml节点列表中选择单个节点？

我在C中有一个XmlDocument对象，其结构如下：

<?xml version="1.0"?>
<catalog>
   <book id="bk101">
      <author>Gambardella, Matthew</author>
      <title>XML Developer's Guide</title>
      <genre>Computer</genre>
      <price>44.95</price>
      <publish_date>2000-10-01</publish_date>
      <description>An in-depth look at creating applications 
      with XML.</description>
   </book>
   <book id="bk102">
      <author>Ralls, Kim</author>
      <title>Midnight Rain</title>
      <genre>Fantasy</genre>
      <price>5.95</price>
      <publish_date>2000-12-16</publish_date>
      <description>A former architect battles corporate zombies, 
      an evil sorceress, and her own childhood to become queen 
      of the world.</description>
   </book>
</catalog>

我正在创建一个book节点列表，并循环分配给authors字符串数组。当我尝试

XmlNodeList xnl = xmlDocument.SelectNodes("//catalog/book");
for (int i = 0; i < xnl.Count; i++)
{
    authors[i] = xnl[i].SelectSingleNode("//author").InnerText;
}

我得到一个空引用异常。为什么SelectSingleNode的结果应为空？

请尝试以下方法之一

for (int i = 0; i < xnl.Count; i++)
{
    authors[i] = xnl[i].SelectSingleNode("//author").value;
}

或

试试这个

var all_elements = xmldoc.DocumentElement.SelectNodes("//catalog/book/author");

        foreach(XmlNode sub_elements in all_elements)
        {
            if(sub_elements.InnerText != "")
            {
                string answer = sub_elements.InnerText;
            }
            else
            {
                //null text
            }
        }

---

我认为作者的双斜杠是不必要的，不是吗？除此之外，它看起来是合法的，除非作者给了你例外…@Mitch你是对的。问题是authors数组的大小没有定义。这在我们所有人身上都会发生。它甚至不会编译。

var all_elements = xmldoc.DocumentElement.SelectNodes("//catalog/book/author");

        foreach(XmlNode sub_elements in all_elements)
        {
            if(sub_elements.InnerText != "")
            {
                string answer = sub_elements.InnerText;
            }
            else
            {
                //null text
            }
        }