General Change Notification: 1 Design Goals

General Change Notification allows you to keep track of both system and application events. Objects or processes interested in a particular change may request the GCN mechanism to notify them when that change occurs. That change may be system-wide (such as a file system change) or application-specific (such as a text style change within a word processor). The GCN mechanism allows objects or processes to sign up for such notification and intercept messages sent by the system (or the application) so that you may respond to different changes on a case by case basis.

The manners in which you sign up for these two types of notification differ although the functionality of the notification process is similar. The most straightforward way is to use a gcnList field in an application's application object; this is the usual approach used to add an application's GenPrimary object to the application's window list. We will assume that you know how to add an object to a GCN list in this manner, as it is shown in most if not all of the sample applications.

You can also sign up for system-wide notification through the use of certain routines and intercept system messages when the change occurs. Other objects may sign up for application-specific notification supported by GenApplicationClass . These application specific notifications should only be sent to the GenApplication object.

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2 The Mechanics of GCN