通过

使用 XPathNavigator 提取 XML 数据

可通过多种不同的方式在 Microsoft .NET Framework 中表示 XML 文档。 这包括使用String，或通过使用XmlReader、XmlWriter、XmlDocument或XPathDocument类。 为了便于在 XML 文档的不同表示形式之间移动，该XPathNavigator类提供了许多方法和属性，用于将 XML 提取为对象StringXmlReader或XmlWriter对象。

将 XPathNavigator 转换为字符串

类 OuterXml 的属性 XPathNavigator 用于获取整个 XML 文档的标记，或仅获取单个节点及其子节点的标记。

注释

InnerXml 属性只获取节点的子节点的标记。

下面的代码示例演示如何将对象XPathNavigator中包含的String整个 XML 文档另存为单个节点及其子节点。

Dim document As XPathDocument = New XPathDocument("input.xml")  
Dim navigator As XPathNavigator = document.CreateNavigator()  
  
' Save the entire input.xml document to a string.  
Dim xml As String = navigator.OuterXml  
  
' Now save the Root element and its child nodes to a string.  
navigator.MoveToChild(XPathNodeType.Element)  
Dim root As String = navigator.OuterXml  

XPathDocument document = new XPathDocument("input.xml");  
XPathNavigator navigator = document.CreateNavigator();  
  
// Save the entire input.xml document to a string.  
string xml = navigator.OuterXml;  
  
// Now save the Root element and its child nodes to a string.  
navigator.MoveToChild(XPathNodeType.Element);  
string root = navigator.OuterXml;

将 XPathNavigator 转换为 XmlReader

该方法 ReadSubtree 用于将 XML 文档的全部内容或仅将单个节点及其子节点流式传输到对象 XmlReader 。

当使用当前节点及其子节点创建XmlReader对象时，该对象的XmlReader的ReadState属性设置为Initial。 首次调用XmlReader对象的Read方法时，XmlReader将移动到XPathNavigator的当前节点。 新 XmlReader 对象继续读取，直到到达 XML 树的末尾。 此时，该方法 Read 返回 false ，并且 XmlReader 对象的 ReadState 属性设置为 EndOfFile。

XPathNavigator对象的位置不受XmlReader对象的创建或移动影响。 ReadSubtree仅当定位在元素或根节点上时，该方法才有效。

以下示例展示了如何获取一个XmlReader对象，其中XPathDocument对象包含整个 XML 文档，以及单个节点及其子节点。

Dim document As XPathDocument = New XPathDocument("books.xml")  
Dim navigator As XPathNavigator = document.CreateNavigator()  
  
' Stream the entire XML document to the XmlReader.  
Dim xml As XmlReader = navigator.ReadSubtree()  
  
While xml.Read()  
    Console.WriteLine(xml.ReadInnerXml())  
End While  
  
xml.Close()  
  
' Stream the book element and its child nodes to the XmlReader.  
navigator.MoveToChild("bookstore", "")  
navigator.MoveToChild("book", "")  
  
Dim book As XmlReader = navigator.ReadSubtree()  
  
While book.Read()  
    Console.WriteLine(book.ReadInnerXml())  
End While  
  
book.Close()  

XPathDocument document = new XPathDocument("books.xml");  
XPathNavigator navigator = document.CreateNavigator();  
  
// Stream the entire XML document to the XmlReader.  
XmlReader xml = navigator.ReadSubtree();  
  
while (xml.Read())  
{  
    Console.WriteLine(xml.ReadInnerXml());  
}  
  
xml.Close();  
  
// Stream the book element and its child nodes to the XmlReader.  
navigator.MoveToChild("bookstore", "");  
navigator.MoveToChild("book", "");  
  
XmlReader book = navigator.ReadSubtree();  
  
while (book.Read())  
{  
    Console.WriteLine(book.ReadInnerXml());  
}  
  
book.Close();

该示例将 books.xml 文件作为输入。

<?xml version="1.0" encoding="utf-8" ?> 
<bookstore>
    <book genre="autobiography" publicationdate="1981-03-22" ISBN="1-861003-11-0">
        <title>The Autobiography of Benjamin Franklin</title>
        <author>
            <first-name>Benjamin</first-name>
            <last-name>Franklin</last-name>
        </author>
        <price>8.99</price>
    </book>
    <book genre="novel" publicationdate="1967-11-17" ISBN="0-201-63361-2">
        <title>The Confidence Man</title>
        <author>
            <first-name>Herman</first-name>
            <last-name>Melville</last-name>
        </author>
        <price>11.99</price>
    </book>
    <book genre="philosophy" publicationdate="1991-02-15" ISBN="1-861001-57-6">
        <title>The Gorgias</title>
        <author>
            <name>Plato</name>
        </author>
        <price>9.99</price>
    </book>
</bookstore>

将 XPathNavigator 转换为 XmlWriter

该方法 WriteSubtree 用于将 XML 文档的全部内容或仅将单个节点及其子节点流式传输到对象 XmlWriter 。

创建XPathNavigator对象时，XmlWriter对象的位置保持不变。

以下示例展示了如何获取一个XmlWriter对象，其中XPathDocument对象包含整个 XML 文档，以及单个节点及其子节点。

Dim document As XPathDocument = New XPathDocument("books.xml")  
Dim navigator As XPathNavigator = document.CreateNavigator()  
  
' Stream the entire XML document to the XmlWriter.  
Dim xml As XmlWriter = XmlWriter.Create("newbooks.xml")  
navigator.WriteSubtree(xml)  
xml.Close()  
  
' Stream the book element and its child nodes to the XmlWriter.  
navigator.MoveToChild("bookstore", "")  
navigator.MoveToChild("book", "")  
  
Dim book As XmlWriter = XmlWriter.Create("book.xml")  
navigator.WriteSubtree(book)  
book.Close()  

XPathDocument document = new XPathDocument("books.xml");  
XPathNavigator navigator = document.CreateNavigator();  
  
// Stream the entire XML document to the XmlWriter.  
XmlWriter xml = XmlWriter.Create("newbooks.xml");  
navigator.WriteSubtree(xml);  
xml.Close();  
  
// Stream the book element and its child nodes to the XmlWriter.  
navigator.MoveToChild("bookstore", "");  
navigator.MoveToChild("book", "");  
  
XmlWriter book = XmlWriter.Create("book.xml");  
navigator.WriteSubtree(book);  
book.Close();

示例将本主题前面找到的books.xml文件作为输入。

另请参阅