Applied XML Programming for Microsoft .NET.pdf - Csbdu.in

Readers and XML ReadersTo cap off our examination of XML readers and custom readers, let's spend a fewmoments looking at the difference between an XML reader and a generic reader for anon-XML data structure.A reader is a basic and key concept in the .NET Framework. Several different types ofreader classes do exist in the .NET Framework: binary readers, text readers, XMLreaders, and database readers, just to name a few. Of course, you can add your owndata-specific readers to the list. But that's the point. How would you write your newreader? The simplest answer would be, you write the reader by inheriting from one ofthe existing reader classes.A more precise answer should help you identify the best reader class to start from. Thekey criterion when you're choosing a base class is the kind of programming interfaceyou expect from the new reader. Another minor, but not negligible, concern is whetherthe class allows for inheritance. Some reader classes are sealed and do not permitinheritance. (The data reader classes, such as SqlDataReader, belong to thiscategory.)Actually, you could build your own reader class from base classes such asBinaryReader, TextReader, and XmlReader. Typically, you choose the BinaryReaderclass if you need to manipulate primitive types in binary rather than text format. Youchoose the TextReader class whenever character input is critical. To successfully buildon top of TextReader, the most complicated thing you might need to do is read a line oftext between two successive instances of a carriage return. You choose the XmlReaderclass as the base class if the content of the data you expose can be rendered, or atleast traversed, as XML. Because XML is a very specific flavor of text, the XmlReaderclass happens to be more powerful and richer than any other reader class. Not all data,however, maps to some reasonable extent to XML. If this is the case, simply plan abrand-new reader on top of BinaryReader or TextReader as applicable.If you just want to implement a specialized XML reader (for example, a SAX reader oran XML reader supporting a different visiting algorithm), you might also considerstarting from XmlTextReader, XmlNodeReader, or XmlValidatingReader. An XMLspecialized reader is basically a reader designed to handle data that is natively storedas well-formed XML.ConclusionSo far, we've covered the basics of XML readers. By now, you should know how toparse an XML document irrespective of its physical location and storage medium. Youknow how to move between nodes, how to skip unneeded nodes, and how to readcontents and attributes. In short, you have gotten the gist of XML readers.The reader is a general concept that crosses the whole spectrum of .NET Frameworkfunctionalities and applies to XML as well as databases, files, and network protocols.You can also create custom XML readers to process non-XML data structures such asCSV files.We've only scratched the surface of this topic—there's a lot more to be done. Forexample, we haven't yet looked at validation, which is the topic of Chapter 3.59