Data Storage and Retrieval

Using Newton Data Storage Objects

control how and when notifications are sent

The first part of this section describes how to register and unregister a callback
function for execution in response to changes in a particular soup. The next part
describes the various notifications that may be sent. The last part of this section
describes how applications send soup change notifications.

Registering Your Application for Change Notification

11

The

RegSoupChange

global function registers a callback function for execution

in response to changes in a particular soup. Note that this callback function must
not call either of the

RegSoupChange

or

UnRegSoupChange

functions.

If your application needs to respond to changes in more than one soup, you'll need
to call the

RegSoupChange

function once on each soup for which your

application requires change notification. This approach is valid for any system-
supplied soup except that used by the built-in Preferences application. For
notification of changes to user preferences, you must call the

RegUserConfigChange

function.

You can call the

RegSoupChange

function at any time that makes sense for your

application. For example, you might do so from within your base view's

viewSetupDoneScript

method; however, this is only a suggested guideline. In

order to conserve available memory, your application should minimize the amount
of time callback functions remain registered.

The following code example shows how to register your application for notification
of changes to the soup used by the built-in Names application:

local myFn := func (soupName, appSym, changeType, changeData)

begin

if (changeType) then

begin
if (changeType <> 'whatThe) then

print (changeType && "in the" && soupName &&

"soup by the" && GetAppName(appSym) &&
"application.");

else

print ("Unspecified changes occurred in the" &&

soupName && "soup.");

end;

end;

// register for changes to soup used by built-in "Names" app
RegSoupChange(ROM_CardFileSoupName, '|myFn1:MyApp:MySig|, myFn);