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

get{ReadOnlyNameValueCollection o = GetConfig("appSettings");if (o == null){o = new ReadOnlyNameValueCollection();o.IsReadOnly = true;}}return o;}Internally, the GetConfig method first determines the name and location of theconfiguration file to access and then proceeds by creating a specialized XML textreader to operate on the XML document. Each XML node read is parsed and thecontents stored as name/value pairs in a ReadOnlyNameValueCollection object. Toparse the contents of each XML node found, the method uses an instance of thesection handler class specified in the section declaration within the block. To read the section, GetConfig resorts to theNameValueSectionHandler handler. This handler parses all the nodes below and adds entries to the collection. We'll look at section handler objectsin more detail in the section "Customizing the XML Schema for Your Data," on page646.The Section HandlerIn our sample machine.config file, the section is read through aninstance of the NameValueFileSectionHandler class. What's the difference betweenthis class and the NameValueSectionHandler class?The MSDN documentation doesn't provide further information about theNameValueFileSectionHandler class; it notes only that the class is intended to be usedonly by the .NET Framework. But the NameValueFileSectionHandler class is actually awrapper for NameValueSectionHandler class, which provides an extra, althoughundocumented, feature. In particular, the NameValueFileSectionHandler sectionhandler allows the application settings to be stored in a separated file in accordancewith the following syntax:The file pointed to by the file attribute is read as if it is an section in theconfiguration file. Note that the root element of the myfile.config file must match thesection that refers to it. So if the file attribute belongs to the section, theroot element of the file being pointed to must be named .The NameValueFileSectionHandler object processes the contents of the embedded fileusing the NameValueSectionHandler class. If no file is embedded in the section but the default documented schema is used, the two section handlers arefunctionally equivalent.Although undocumented, the following code represents a perfectly valid schema for theapplication's configuration file. The sample application AppSettings, available in thisbook's sample files, demonstrates how to take advantage of this syntax.511