XPathNavigator.ReadSubtree Method

Definition

Namespace:

System.Xml.XPath

Assembly:

System.Xml.ReaderWriter.dll

Source:

XPathNavigator.cs

Returns an XmlReader object that contains the current node and its child nodes.

public:
 virtual System::Xml::XmlReader ^ ReadSubtree();

public virtual System.Xml.XmlReader ReadSubtree ();

abstract member ReadSubtree : unit -> System.Xml.XmlReader
override this.ReadSubtree : unit -> System.Xml.XmlReader

Public Overridable Function ReadSubtree () As XmlReader

Returns

XmlReader

An XmlReader object that contains the current node and its child nodes.

Exceptions

InvalidOperationException

The XPathNavigator is not positioned on an element node or the root node.

Examples

The following example illustrates using the ReadSubtree method on the first book element of the contosoBooks.xml file.

XPathDocument^ document = gcnew XPathDocument("contosoBooks.xml");
XPathNavigator^ navigator = document->CreateNavigator();

navigator->MoveToChild("bookstore", "http://www.contoso.com/books");
navigator->MoveToChild("book", "http://www.contoso.com/books");

XmlReader^ reader = navigator->ReadSubtree();

while (reader->Read())
{
    Console::WriteLine(reader->ReadInnerXml());
}

reader->Close();

XPathDocument document = new XPathDocument("contosoBooks.xml");
XPathNavigator navigator = document.CreateNavigator();

navigator.MoveToChild("bookstore", "http://www.contoso.com/books");
navigator.MoveToChild("book", "http://www.contoso.com/books");

XmlReader reader = navigator.ReadSubtree();

while (reader.Read())
{
    Console.WriteLine(reader.ReadInnerXml());
}

reader.Close();

Dim document As XPathDocument = New XPathDocument("contosoBooks.xml")
Dim navigator As XPathNavigator = document.CreateNavigator()

navigator.MoveToChild("bookstore", "http://www.contoso.com/books")
navigator.MoveToChild("book", "http://www.contoso.com/books")

Dim reader As XmlReader = navigator.ReadSubtree()

While reader.Read()
    Console.WriteLine(reader.ReadInnerXml())
End While

reader.Close()

The example takes the contosoBooks.xml file as an input.

<?xml version="1.0" encoding="utf-8" ?>  
<bookstore xmlns="http://www.contoso.com/books">  
    <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>  

Remarks

When the XmlReader object is created with the current node and its child nodes, the XmlReader object's ReadState property is set to Initial. When the XmlReader object's Read method is called for the first time, the XmlReader is moved to the current node of the XPathNavigator. The new XmlReader object continues to read until the end of the XML tree is reached. At this point, the Read method returns false and the XmlReader object's ReadState property is set to EndOfFile.

Note

Changing the position of the XmlReader object does not affect the position of the XPathNavigator.

Namespace declarations for the in-scope namespaces of the current node are not inserted into the XML stream provided to the XmlReader object.

Note

This behavior differs from the WriteSubtree method.

This method creates the XmlReader object with specific reader settings, and the module that uses this method has no control over those settings. For example, the reader returned by this method prohibits processing Data Type Definitions (DTDs). If the reader attempts to read a file that uses a DTD, it will throw an error, XmlException. The message for the exception will be Unexpected DTD declaration.

You can change this behavior by implementing a custom XmlResolver that returns an XmlReader with the desired XmlReaderSettings.