Apple Newton Utilities User's Guide download pdf (Page 497)

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CHAPTER 11

Data Storage and Retrieval

Using Newton Data Storage Objects 11-65

▲ W ARNING

Any callback function registered by the RegSoupChange

function must not call either of the

RegSoupChange or

UnRegSoupChange functions. ▲

The second argument to the RegSoupChange function can be any unique symbol

that identiﬁes the callback to be registered. If your application registers only one

callback function, you can just use your application symbol as the callback

identiﬁer (ID). A callback ID need only be unique within the registry that uses it.

For example, no two power registry callback functions can share the same callback

ID; on the other hand, your application’s power registry callback can use the same

ID as your application’s login screen callback. Thus, if your application only

registers one callback function with each of the various registries, all of your

callback functions can use your application symbol (with developer signature) as

their callback ID.

To generate unique identiﬁers for multiple callbacks within the same registry, you

can preﬁx an additional identiﬁer to your application symbol. For example, the

symbol

'|myFn1:MyApp:MySig| could be used to identify one of several

callback functions registered by the

MyApp:MySig application.

Unregistering Your Application for Change Notiﬁcation 11

When your application no longer needs to be notiﬁed of changes to a particular

soup, it needs to call the

UnRegSoupChange function to unregister its callback

function for that soup.

// unregister my app’s Names soup callback

UnRegSoupChange(ROM_CardFileSoupName, '|myFn1:MyApp:MySig|);

Normally, you can unregister your soup change callbacks in the viewQuitScript

method of your application’s base view.

Responding to Notiﬁcations 11

When a soup changes in some way, the system executes the callback functions

registered for that soup. Note that the system does not consider the soup to have

changed until an entry is written to the soup. Thus, changing a cached entry is not

considered a change to the soup until the

EntryChangeXmit function writes the

cached entry back to the soup.

Note

The system-supplied Preferences application sends

soup change notiﬁcations only if your application

uses the

RegUserConfigChange function to register

for such notiﬁcations.

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