Apple Newton Utilities Uživatelská příručka stáhnout pdf (Strana 641)

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CHAPTER 17

Additional System Services

Using Additional System Services 17-25

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);

IMPORTANT

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

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