Advanced XmlSerializer

The .NET framework offers more ways to process XML than just parsing it. The System.Xml.Serialization namespace contains classes to create an XML representation for an object or initialize an object directly from XML.  The focus of this of this chapter was on developing classes with an XML representation conforming to the XSD standard, which is widely used to describe XML formats in data exchange scenarios.

Using XML serialization will reduce the amount of code you have to develop for an XML-based data exchange application. You no longer have to parse XML to initialize objects, neither do you have to develop code for objects to persist themselves to XML. Once you defined what the XML format you use to exchange data looks like, you can quickly develop classes that can automatically store their data to the XML format or objects can be automatically created from XML.

Besides the runtime support for serialization, the .NET Framework also supplies a tool to generate source code for serializable classes from XSD schemas. Once you start developing solutions with XSD schemas and XML serialization make sure you read the chapter read about the XSD schema definition tool chapter in the appendix.

Previously we introduced XML serialization. We learned how classes are mapped to XML when we transform them with the XmlSerializer. We can use the techniques we learned to quickly develop an XML-driven application and get the best of both worlds: Objects for programming and XML for data transfer or storage. The XmlSerializer does the transformations from one representation to the other.

This will cover some advanced techniques for customizing output of the XmlSerializer. We focused on developing classes to match an XML format from scratch. Unfortunately there are some scenarios where this is not good enough. Real world projects usually include classes where we can not just go and attach an attribute when the class does not exactly map to the XML format we need, so we will learn how to customize XML serialization at run-time. We will also learn to manage namespaces in the serialized XML and how to inject and retrieve XML that does not map to any class members.

You need to be familiar with the basics: How to attach metadata attributes to classes in order to customize their XML representation as well as some other concepts explained in the previous chapter. You also need to be familiar with:

• The XmlNode class hierarchy
• Events and delegates.
• XML Namespaces

Events and Delegates

Events and Delegates are a programming concept heavily used throughout the .NET programming model. They provide an object-oriented and type-safe model to register call-back methods. When a class exposes an event of a delegate type other classes can bind event handlers to the event to receive event notifications. If you’re not already familiar with the use of .NET events you can find a deeper discussion on event and delegates in the .NET Framework SDK documentation.

XML Namespaces

Often applications need to add new information to existing XML documents or combine existing XML documents. To avoid naming conflicts in these scenarios (“from which document is the <description> element?”), the W3 consortium standardized XML namespaces. You can think of a namespace as a last name for elements and attributes. Calling for somebody in a crowd just by their first name might cause many people to respond, if you call for somebody by their first and last name you can address the right person. XML namespaces work the same way: the first name is an XML element or attribute; the last name is the namespace URI. Using both, you can uniquely identify attributes and elements in an XML document.