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C H A P T E R 1 7
Additional System Services
About Additional System Services
a function object to redo the original function or method. Thus tapping the Undo
button twice completes an undo/redo cycle.
Undo Compatibility
The user interface standards for version 2.0 of the Newton operating system call for
the user's second tap on the Undo button to provide a Redo rather than a second
level of Undo. Your undo action must create an undo action for itself to implement
this interface. For more information, see the section "Using Undo Actions"
beginning on page 17-8.
The global function
is obsolete, replaced by the view method of
the same name that provides similar functionality. Existing code that uses the
global function can be converted by prefixing a colon to the message selector.
For example:
Idler Objects
An idler object sends a message to your view periodically to execute the
method you provide for that view. This allows you to perform
periodic tasks from any view for which you have installed an idler object.
Note, however, that the time the
message is sent is not
guaranteed to be the exact interval you specify. This is because the idler
may be delayed if a method is executing when the interval expires. The
message cannot be sent until an executing method returns.
Change Notifications
The system provides notification services send your application a message when a
soup, folder, or user configuration variable has been changed. These are described
in the following chapters:
The soup change notification service is discussed in Chapter 11, "Data Storage
and Retrieval."
The folder change notification service is discussed in Chapter 15, "Filing."
The user configuration change notification service is discussed in Chapter 19,
"Built-in Applications and System Data."
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