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About Additional System Services
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C H A P T E R 1 7
Additional System Services
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Figure 17-0
Table 17-0
This chapter discusses system services not covered elsewhere in this book. The
topics covered in this chapter are
Providing the capability to undo and redo user actions.
Using idler objects to perform periodic operations.
Using the notification service to respond to soup, folder, or user configuration
change messages.
Using the alerts and alarms service to display user messages and execute
callback functions at specified times.
Using progress indicators to provide user feedback.
Using the power registry to execute callback functions when the Newton is
powered on or off.
Using a custom help book to provide online help to the user.
If you are developing an application that utilizes any of these objects or services,
you should familiarize yourself with the material discussed in this chapter.
About Additional System Services
17
This section briefly describes the undo, idler objects, alerts and alarms, change
notification, progress reporting, and power registry services. These are discussed in
greater detail later in this chapter.
Undo
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The Undo service is the mechanism the system provides for undoing and redoing
the user's most recent action. From within each function or method that must
support Undo, your application registers a function object that can reverse the
actions of that function or method. This function object is called an undo action,
and is called when the user taps the Undo button. The undo action can then register
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