.NET & XML

XmlReader

XmlReader is an abstract base class that provides an event-based, read-only, forward-only XML pull parser (I’ll discuss each of these terms shortly). XmlReader has three concrete subclasses, XmlTextReader, XmlValidatingReader, and XmlNodeReader, which enable you to read XML from a file, a Stream, or an XmlNode. You can also extend XmlReader to read other, non-XML data formats, and deal with them as if they were XML (you’ll learn how to do this in Chapter 4).

The base XmlReader provides only the most essential functionality for reading XML documents. It does not, for example, validate XML (that’s what XmlValidatingReader does) or expand XML entities into their respective character data (though XmlTextReader does). This does not mean that XML read from a text file cannot be validated at all; you can validate XML from any source by using the XmlValidatingReader constructor that takes an XmlReader object as a parameter, as I’ll demonstrate.

Here are those four terms I used to describe XmlReader again, with a little explanation.

Event-based

An event in a stream-based XML reader indicates the start or end of an XML node as it is read from the data stream. The event’s information is delivered to your application, and your application takes some action based on that information. In XmlReader, events are delivered by querying XmlReader’s properties after calling its Read( ) method.

Read-only

XmlReader , as its name implies, can only read XML. For writing XML, there is an XmlWriter ...