Apple Newton Utilities Guide de l'utilisateur télécharger pdf (Page 498)

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CHAPTER 11

Data Storage and Retrieval

11-66 Using Newton Data Storage Objects

Your callback function must take any action that is appropriate to respond to the

change. Most applications have no need to respond to soup changes unless they are

open, which is why it is recommended that you register your callbacks when your

application opens and unregister them when it closes.

The arguments passed to your callback function include the name of the soup that

changed, the symbol identifying the callback function to execute, the kind of

change that occurred, and optional data such as changed soup entries. For a simple

code example, see “Registering Your Application for Change Notiﬁcation”

beginning on page 11-64. For a complete description of the callback function and

its parameters, see the section “Callback Functions for Soup Change Notiﬁcation”

(page 9-14) in Newton Programmer’s Reference.

▲ W ARNING

The 'soupEnters and 'soupLeaves messages are guaranteed

to be sent only when a reference to the changed soup exists. These

messages may not be sent for soups that are not in use. For

example, if no cursor object references the soup, this message

may not be sent.

▲

Sending Notiﬁcations 11

When your application alters a soup, it may need to notify other applications that

the soup has changed. The best means of doing so depends on the exact nature

of the change.

The system provides functions and methods that transmit change notiﬁcation

messages automatically after altering soups, union soups, or entries. The names of

these auto-transmit routines end with the

-Xmit sufﬁx. They are described

throughout this chapter in sections pertaining to the main behaviors they provide,

such as adding frames to soups as entries, changing entries, and so on.

The auto-transmit (

fnOrMethodNameXmit) routines provide the easiest and best

way to send notiﬁcations when making a limited number of changes to a soup. For

example, to save a frame in a union soup and transmit an appropriate notiﬁcation

message, use the

AddToDefaultStoreXmit method as shown in the following

code fragment:

// get soup in which to save the new entry

local myUSoup := GetUnionSoupAlways("myUSoup:mySig");

// frame to add as new entry

local myFrame := {name: Daphne, color: tabby};

// add the entry and transmit change notification

local ent := myUSoup:AddToDefaultStoreXmit(myFrame,'|MyApp:MySig|);

The auto-transmit methods and functions accept a changeSym parameter identifying

the application that changed the soup. If you pass

nil for the value of the

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