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

CautionI tried to keep this version of the CSV reader as simple aspossible, which is always a good guideline. In this case,however, I went beyond my original intention and came up with atoo simple reader! Don't be fooled by the fact that the samplecode discussed here works just fine. As I built it, the CSV readerdoes not expose the CSV document as a well-formed XMLdocument, but rather as a well-formed XML fragment. There isno root node, and no clear distinction is made between start andend element tags. In addition, the ReadAttributeValue method isnot supported. As a result, if you use ReadXml to load the CSVinto a DataSet object, only the first row would be loaded. If yourun the CsvReader sample included in this book's sample files,you'll see an additional button on the form labeled UseReadXML, which you can use to see this problem in action. InChapter 9, after a thorough examination of the internals ofReadXml, we'll build an enhanced version of the CSV reader.The DataGrid control shown in Figure 2-2 is read-only, but this does not mean that youcan't modify rows in the underlying DataTable object and then save changes back tothe CSV file. One way to accomplish this result would be by using a customized XMLwriter class—a kind of XmlCsvWriter. You'll learn how to create such a class in Chapter4, while we're looking at XML writers.NoteThe full source code for both the CSV XML reader and the sampleapplication making use of it is available in this book's sample files.The folder of interest is named CsvReader.ImportantThe XmlTextReader class implements a visiting algorithm forthe XML tree based on the so-called node-first approach. Thismeans that for each XML subtree found, the root is visited first,and then recursively all of its children are visited, from the firstto the last. Node-first is certainly not the most unique visitingalgorithm you can implement, but it turns out to be the mostsensible one for XML trees.Another well-known visiting algorithm is the in-depth-firstapproach, which goes straight to the leaves of the tree andthen pops back to outer parent nodes. The node-first approachis more effective for XML trees because it visits nodes in theorder they are written to disk. Choosing to implement adifferent visiting algorithm would make the code significantlymore complex and less effective from the stand-point ofmemory footprint. In short, you should have a good reason toplan and code any algorithm other than node-first.In general, visiting algorithms other than node-first algorithmsexist mostly for tree data structures, including well-balancedand binary trees. XML files are designed like a tree datastructure but remain a very special type of tree.58