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

Table 15-2: Predefined Section HandlersClassDictionarySectionHandlerIgnoreSectionHandlerNameValueFileSectionHandlerNameValueSectionHandlerSingleTagSectionHandlerDescriptionReads name/value pairs and groups themin a hash table object.The System.Configuration classes ignorethe sections marked with this handlerbecause their contents will be processedby other components. This handler is analternative to using and declaring customhandlers.Reads name/value pairs from a filereferenced in the sectionand groups them in aNameValueCollection object.Reads name/value pairs and groups themin a NameValueCollection object.Reads settings from attributes stored in asingle XML node. The data is returned asa hash table.In the .NET Framework, the classes in the System.Configuration namespace areresponsible for parsing the contents of the configuration files. These classes aredesigned to process the entire contents of the configuration files. The classes alsothrow an exception when a configuration section lacks a corresponding entry in the block and when the layout of the data does not match the declaration.Of the five section handlers, we have examined NameValueSectionHandler andNameValueFileSectionHandler. The DictionarySectionHandler class is very similar; itdiffers only in that it stores settings in a hash table instead of in a NameValueCollectionobject. Collection objects are more efficient if they are used to store a small number ofitems (ideally fewer than 10), whereas a hash table provides better performance withlarge collections of items. The IgnoreSectionHandler and SingleTagSectionHandlerclasses deserve a bit more attention, and we'll look at them next.The IgnoreSectionHandler Section HandlerA few subsystems in the .NET Framework store configuration data in themachine.config file but process the data themselves, without relying on the servicesprovided by the System.Configuration classes. For example, the machine.config filecontains remoting and startup information that is processed outside the configurationengine. To prevent the configuration file from parsing exceptions, you can use a dummysection handler—IgnoreSectionHandler. This handler handles sections of configurationdata rather than relying on the classes in System.Configuration. It could be argued thatsuch data should be stored in a system configuration file, like the machine.config file, orin a custom file. Looking at the following excerpt from the machine.config file, you cansee that remoting configuration settings are processed by the remoting classes,whereas HTTP run-time configuration settings are processed by a custom handler:518