Environment change notifier

A change notifier is provided so that an application can be notified of changes in the environment such as a switch in locale, crossing over past midnight etc. The TChanges enumerator lists the possible events. This set of events may be extended as the operating system evolves.

An environment change notifier is an instance of a CEnvironmentChangeNotifier class. This is an active object which allows an application to respond to change events easily. These change events are generated by a Kernel side change notifier service. The CEnvironmentChangeNotifier class uses the Kernel side change notifier service through an RChangeNotifier handle.

An application supplies a call back function to CEnvironmentChangeNotifier when it is constructed.

When an outstanding request for change events completes, CEnvironmentChangeNotifier issues another request for change events before calling the callback function.

The implementation of the callback function depends on the application but, typically, it would flag the changes of interest and, perhaps, schedule other changes either to the application's engine or the application's user interface.