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

NoteUser applications don't need to declare the sectionbecause the section is already declared in the system'smachine.config file, as we saw in the section "MachineConfiguration Files," on page 626. You don't need to repeat the declaration unless you want to modify some of theattributes, including the name/value format of the settings.The ConfigurationSettings ClassTo programmatically read application settings, you use the ConfigurationSettings class.ConfigurationSettings is a small, sealed class that simply provides one static method(GetConfig) and one static property (AppSettings).The AppSettings property is a read-only NameValueCollection object designed to getthe information stored in the section. If no setting is specified, or if no section exists, an empty collection is returned.NoteTo have a read-only NameValueCollection object, you need to usea class that derives from NameValueCollection and sets theprotected member IsReadonly to true. This is exactly what happensunder the hood of the AppSettings property. The helper collectionclass that the AppSettings property returns is an undocumentedclass named ReadOnlyNameValueCollection.The GetConfig method returns the configuration settings for the specified section, asshown here:public static object GetConfig(string sectionName);Although the method signature indicates an object return type, the actual return valueyou get from a call to GetConfig is a class derived from NameValueCollection. Inparticular, the class is ReadOnlyNameValueCollection if the section is .NoteIn general, the object returned by GetConfig is determined by thehandler class specified for the section. If the handler isNameValueSectionHandler or a related class, you get settingsstored in a name/value collection. As we'll see chapter in the section"Types of Section Handlers," on page 640, other options exist thatcould result in a different way of packing settings for applications.The AppSettings property acts as a wrapper for the GetConfig method. The actualimplementation of the property consists of a call to GetConfig in which the section namedefaults to . The following pseudocode demonstrates:public static NameValueCollection AppSettings{get {return GetConfig("appSettings");}}The real code is a bit more sophisticated than this, however. After GetConfig returns,the get accessor verifies that the returned value is not null. GetConfig returns null if thespecified section is empty or does not exist. If the returned object is null, the getaccessor of the AppSettings property creates an empty collection and returns that tothe caller. The pseudocode is shown here:public static NameValueCollection AppSettings{510