Additional System Services

Using Additional System Services

Registering Login Screen Functions

17

If you want a power-on function that brings up some sort of visible component,
you should register that function as login function. These functions are only called
after the login screen has been displayed and the password entered (if the user has
installed a password). Note that future Newton devices may not support the login
screen. In this case the login functions will still be executed.

The methods that register login functions are defined in the

sleepScreen view

,

to get a reference to the

sleepScreen

view to send it

RegLogin

and

UnRegLogin

messages, use code such as:

GetRoot().sleepScreen:RegLogin(callBackFn,callBackFnArgs);

The callback function registered with

RegLogin

must not itself

call

RegLogin

nor

UnRegLogin

.

Registering Power-Off Functions

17

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

RegPowerOff

function. As with power-on functions, when the

Newton is powered off, the system passes a symbol to your "shutdown" callback
function indicating the reason it was called. This symbol, passed as the value of
your callback's why parameter, allows it to condition its actions according to the
way the system was powered off. The

'user

symbol indicates that the user

initiated the shutdown. The

'idle

symbol indicates the system initiated shutdown

after the Newton was left idle for the period of time specified by the user's Sleep
preferences. The

'because

symbol indicates that the Newton powered off for

some other unspecified reason.

The system also passes a symbol to your callback function indicating the current
status of the shutdown operation. This symbol is passed as the value of your
callback's what parameter. The value of this parameter is used as the basis for
the cooperative shutdown process. Your callback function must return a value
indicating whether to continue the power-off sequence or delay it. This value is
passed to all registered shutdown functions, allowing each to indicate whether it is
ready to shut down or needs time to complete a task.

The

'okToPowerOff

symbol indicates that the system has received a request to

shut down. In response to the

'okToPowerOff

symbol, your callback can return

true

to specify that shutdown may continue, or it can return

nil

to cancel the

shutdown process. Note that an

'okToPowerOff

symbol does not guarantee that

shutdown will occur--another callback function may cancel the power-off sequence.

The

'powerOff

symbol indicates that shutdown is imminent. If the callback

function must first perform an operation asynchronously, such as the disposal of a