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XPathNavigator.ReadSubtree Method

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

Namespace:  System.Xml.XPath
Assembly:  System.Xml (in System.Xml.dll)

public virtual XmlReader ReadSubtree()

Return Value

Type: System.Xml.XmlReader
An XmlReader object that contains the current node and its child nodes.

ExceptionCondition
InvalidOperationException

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

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.

NoteNote

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.

NoteNote

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.

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

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();

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>

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1
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