为什么XPathNodeIterator找不到所需的路径？

Question

我在使用XPathNodeIterator从给定路径中获取数据时遇到问题。调试时，pNav具有xml文件中的所有值。但是，迭代器的计数为0。它永远不会进入while循环。任何帮助，将不胜感激。

C＃

XPathDocument pdoc = new XPathDocument("Courses.xml");
XPathNavigator pNav = pdoc.CreateNavigator();
XPathNodeIterator iterator = pNav.Select("/Courses/Course");
while (iterator.MoveNext())
{
   XPathNodeIterator it = iterator.Current.Select("Name");
   it.MoveNext();
   string courseName = it.Current.Value;
   it = iterator.Current.Select("Code");
   it.MoveNext();
   string courseCode = it.Current.Value;
   Console.WriteLine("{0} {1}", courseName, courseCode);
}

XML：

<Courses xmlns="http://xml" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="Courses.xsd">
<Course>
<Code Undergrad="240"/>
<Name>Biology</Name>
<Instructor>
<Name>
   <First>John</First>
   <Last>Doe</Last>
</Name>
<Contact>
   <Phone>898-989-8989</Phone>
</Contact>
</Instructor>
<Room>515</Room>
</Course>

我希望输出是

Name = Biology, Code = 240

Answer 1

因为您有

xmlns="http://xml"

在XML文件中，您需要添加XmlNamespaceManager以允许导航器找到节点。如果从XML中删除xmlns="http://xml"，则不需要使用XmlNamespaceManager。

也Select方法返回节点的集合-您需要调用SelectSingleNode以获取所需的节点。 E.G。

XPathDocument pdoc = new XPathDocument("Courses.xml");
XPathNavigator pNav = pdoc.CreateNavigator();

var manager = new XmlNamespaceManager(pNav.NameTable);
manager.AddNamespace("cs", "http://xml");

XPathNodeIterator iterator = pNav.Select("/cs:Courses/cs:Course", manager);

while(iterator.MoveNext())
{
    var nameNode = iterator.Current.SelectSingleNode("cs:Name", manager);
    string courseName = nameNode.Value;

    var codeNode = iterator.Current.SelectSingleNode("cs:Code", manager);

    codeNode.MoveToFirstAttribute();

    string courseCode = codeNode.Value;
    Console.WriteLine("{0} {1}", courseName, courseCode);
}

[当您到达Code元素时，您需要移至第一个属性以获取该值，否则Value属性将返回一个空字符串

Answer 2

需要将namespace resolver传递给选择方法：

const string xml = @"
    <Courses xmlns=""http://xml"" xmlns:xsi=""http://www.w3.org/2001/XMLSchema-instance"" xsi:schemaLocation=""Courses.xsd"">
        <Course>
            <Code Undergrad=""240""/>
            <Name>Biology</Name>
            <Instructor>
                <Name>
                    <First>John</First>
                    <Last>Doe</Last>
                </Name>
                <Contact>
                <Phone>898-989-8989</Phone>
                </Contact>
            </Instructor>
            <Room>515</Room>
        </Course>
        <Course>
            <Code Undergrad=""000""/>
            <Name>Math</Name>
            <Instructor>
                <Name>
                    <First>John</First>
                    <Last>Doe</Last>
                </Name>
                <Contact>
                <Phone>898-989-8989</Phone>
                </Contact>
            </Instructor>
            <Room>515</Room>
        </Course>
    </Courses>";

using (var stream = new MemoryStream(Encoding.ASCII.GetBytes(xml)))
{
    var pdoc = new XPathDocument(stream);
    var pNav = pdoc.CreateNavigator();

    var manager = new XmlNamespaceManager(pNav.NameTable);
    manager.AddNamespace("cs", "http://xml");

    var iterator = pNav.Select("/cs:Courses/cs:Course", manager);

    foreach (XPathNavigator node in iterator)
    {
        var courseName = node.SelectSingleNode("cs:Name", manager)?.Value;
        var courseCode = node.SelectSingleNode("cs:Code", manager)?.GetAttribute("Undergrad", string.Empty);

        Console.WriteLine("{0} {1}", courseName, courseCode);
    }
}