Using the power registry 17 – Apple Newton Programmer’s Newton 2.0 (for Newton 2.0) User Manual

Page 640

C H A P T E R 1 7

Additional System Services

17-24

Using Additional System Services

Because the

ViewSet

method rebuilds and updates all the status slip’s child views,

you’ll obtain better performance by calling

UpdateIndicator

rather than

ViewSet

when you just need to update the gauge view. The

UpdateIndicator

method rebuilds and updates only the gauge, barber pole, and

progress sheet views.

Implementing a CancelRequest Method

If your status slip provides a “Stop” or “Cancel” button, you may include a

ButtonClickScript

with the button or write a

CancelRequest

method to

handle the necessary housekeeping. The

CancelRequest

method can be

implemented either in the status slip or in the application (or transport) base view.
The system checks if the status slip has a

CancelRequest

method, and if not

sends this message to the application (or transport) base view.

Using the Power Registry

This section describes the cooperative model that Newton devices use to turn
power on and off, and the battery information functions.

Registering Power-On Functions

You may register functions to be called when a Newton device is powered on with
the

RegPowerOn

function. When the Newton device is powered on, the system

calls your “power-on” callback function passing it a symbol indicating the reason it
was called. This allows your code to condition its actions accordingly. For example,
you might perform one set of actions when the user presses the power switch and
another set of actions when the device is powered on by the execution of an alarm.

The

'user

symbol indicates that the user pressed the power switch. The

'emergencyPowerOn

symbol is passed any time the Newton device is powered

up after an emergency power-off. An emergency power-off is any shutdown in
which one or more power-off scripts did not execute. The

'serialgpi

symbol

indicates the presence of +5 volts on the serial port general-purpose input pin (pin
7). The

'alarm

symbol indicates that the power-on was caused by the execution

of an alarm. The

'cardlock

symbol indicates that a PCMCIA card was inserted

or removed.

The

UnRegPowerOn

function unregisters functions added with

RegPowerOn

IMPORTANT

The callback function registered with

RegPowerOn

must not

itself call

RegPowerOn

nor

UnRegPowerOn

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