Apple Newton Utilities Guide de l'utilisateur Page 618

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CHAPTER 17
Additional System Services
17-2 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 17
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
AddUndoAction is obsolete, replaced by the view method of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 prexing a colon to the message selector.
For example:
AddUndoAction(....)
becomes
:AddUndoAction(...)
Idler Objects 17
An idler object sends a message to your view periodically to execute the
ViewIdleScript 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
ViewIdleScript 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
ViewIdleScript message cannot be sent until an executing method returns.
Change Notications 17
The system provides notication services send your application a message when a
soup, folder, or user conguration variable has been changed. These are described
in the following chapters:
The soup change notication service is discussed in Chapter 11, “Data Storage
and Retrieval.
The folder change notication service is discussed in Chapter 15, “Filing.
The user conguration change notication service is discussed in Chapter 19,
“Built-in Applications and System Data.
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