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Learn more about: Reading XML Data using XPathDocument and XmlDocument
Reading XML Data using XPathDocument and XmlDocument
03/30/2017
csharp
vb
5711b225-6aa2-4e4f-9898-19f2d518ad1a

Reading XML Data using XPathDocument and XmlDocument

There are two ways to read an XML document in the xref:System.Xml.XPath?displayProperty=nameWithType namespace. One is to read an XML document using the read-only xref:System.Xml.XPath.XPathDocument class and the other is to read an XML document using the editable xref:System.Xml.XmlDocument class in the xref:System.Xml?displayProperty=nameWithType namespace.

Reading XML Documents using the XPathDocument Class

The xref:System.Xml.XPath.XPathDocument class provides a fast, read-only, in-memory representation of an XML document using the XPath data model. Instances of the xref:System.Xml.XPath.XPathDocument class are created using one of its six constructors. These constructors allow you to read an XML document using a xref:System.IO.Stream, xref:System.IO.TextReader, or xref:System.Xml.XmlReader object, as well as the string path to an XML file.

The following example illustrates using the xref:System.Xml.XPath.XPathDocument class's string constructor to read an XML document.

Dim document As XPathDocument = New XPathDocument("books.xml")  
XPathDocument document = new XPathDocument("books.xml");

Reading XML Documents using the XmlDocument Class

The xref:System.Xml.XmlDocument class is an editable in-memory representation of an XML document implementing W3C Document Object Model (DOM) Level 1 Core and Core DOM Level 2. Instances of the xref:System.Xml.XmlDocument class are created using one of its three constructors. You can create a new, empty xref:System.Xml.XmlDocument object by calling the xref:System.Xml.XmlDocument class constructor with no parameters. After calling the constructor, use the xref:System.Xml.XmlDocument.Load%2A method to load XML data into the new xref:System.Xml.XmlDocument object from a xref:System.IO.Stream, xref:System.IO.TextReader, or xref:System.Xml.XmlReader object, as well as the string path to an XML file.

The following example illustrates using the xref:System.Xml.XmlDocument class constructor with no parameters and the xref:System.Xml.XmlDocument.Load%2A method to read an XML document.

Dim document As XmlDocument = New XmlDocument()  
document.Load("books.xml")  
XmlDocument document = new XmlDocument();  
document.Load("books.xml");

Determining the Encoding of an XML Document

An xref:System.Xml.XmlReader object can be used to read an XML document and to create xref:System.Xml.XPath.XPathDocument and xref:System.Xml.XmlDocument objects as shown in the previous sections. However, an xref:System.Xml.XmlReader object may read data that is not encoded and as a result does not provide any encoding information.

The xref:System.Xml.XmlTextReader class inherits from the xref:System.Xml.XmlReader class, provides encoding information using its xref:System.Xml.XmlTextReader.Encoding%2A property, and can be used to create an xref:System.Xml.XPath.XPathDocument object or xref:System.Xml.XmlDocument object.

For more information about the encoding information provided by the xref:System.Xml.XmlTextReader class, see the xref:System.Xml.XmlTextReader.Encoding%2A property in the xref:System.Xml.XmlTextReader class reference documentation.

Creating XPathNavigator Objects

After you have read an XML document into either an xref:System.Xml.XPath.XPathDocument or xref:System.Xml.XmlDocument object, you can create an xref:System.Xml.XPath.XPathNavigator object to select, evaluate, navigate, and in some cases, edit the underlying XML data.

Both the xref:System.Xml.XPath.XPathDocument and xref:System.Xml.XmlDocument classes, in addition to the xref:System.Xml.XmlNode class, implement the xref:System.Xml.XPath.IXPathNavigable interface of the xref:System.Xml.XPath?displayProperty=nameWithType namespace. As a result, all three classes provide a xref:System.Xml.XPath.IXPathNavigable.CreateNavigator%2A method that returns an xref:System.Xml.XPath.XPathNavigator object.

Editing XML Documents using the XPathNavigator Class

In addition to selecting, evaluating, and navigating XML data, the xref:System.Xml.XPath.XPathNavigator class can be used to edit an XML document in some cases, based on the object that created it.

The xref:System.Xml.XPath.XPathDocument class is read-only while the xref:System.Xml.XmlDocument class is editable and as a result, xref:System.Xml.XPath.XPathNavigator objects created from an xref:System.Xml.XPath.XPathDocument object cannot be used to edit an XML document while those created from an xref:System.Xml.XmlDocument object can. The xref:System.Xml.XPath.XPathDocument class should be used to read an XML document only. In cases where you need to edit an XML document, or require access to the additional functionality provided by the xref:System.Xml.XmlDocument class, like event handling, the xref:System.Xml.XmlDocument class should be used.

The xref:System.Xml.XPath.XPathNavigator.CanEdit%2A property of the xref:System.Xml.XPath.XPathNavigator class specifies if an xref:System.Xml.XPath.XPathNavigator object may edit XML data.

The following table describes the value of the xref:System.Xml.XPath.XPathNavigator.CanEdit%2A property for each class.

xref:System.Xml.XPath.IXPathNavigable Implementation xref:System.Xml.XPath.XPathNavigator.CanEdit%2A Value
xref:System.Xml.XPath.XPathDocument false
xref:System.Xml.XmlDocument true

See also