Apple Newton Utilities Guide de l'utilisateur télécharger pdf (Page 629)

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CHAPTER 17

Additional System Services

Using Additional System Services 17-13

The following code example removes all alarms an application has scheduled for

the next ﬁve minutes:

foreach alarmKey in GetAppAlarmKeys(":MyApp:MySig") do

if not (GetAlarm(alarmKey).time > Time() + 5) then

RemoveAlarm (alarmKey);

Removing Installed Alarms 17

The functions RemoveAlarm and RemoveAppAlarms remove a particular alarm

and all of an application’s alarms, respectively. The

RemoveAlarm function takes

the alarm key of the alarm to remove as its single argument. Use of this function is

demonstrated in the code example in “Retrieving Alarm Keys” beginning on

page 17-12.

The

RemoveAppAlarms function takes an alarm key sufﬁx as an argument and

removes all alarms whose key ends with this sufﬁx. For this reason it is important

for all alarms created by a particular application to use alarm keys ending with the

same sufﬁx. If your application’s alarm are not meaningful if your application is

not installed, you should call this function in your application’s

RemoveScript

function.

Common Problems With Alarms 17

This section describes common problems encountered with use of the alarm service.

Problems With Alarm Callback Functions 17

Alarms are kept in a soup; thus, they persist across restarts and installation or

removal of packages. This means that the arguments you pass to your callback

function are also stored in a soup; hence, these arguments are also copied deeply.

(See the description of the

DeepClone function in Newton Programmer’s

Reference.) Therefore, you must avoid indirectly referencing large objects lest

they unnecessarily inﬂate the size of your entries in the alarm soup.

A classic example of accidentally referencing a large object is in dynamically

creating the function object executed with the alarm. Function objects may contain

references to the lexical environment and the current receiver (

self) at the time

they are created. For example, function objects created from a view method reference

the root view through their parent chain. If you pass such a function object to the

AddAlarm function, the system attempts to copy the entire root view into the

alarm soup. One way to minimize the size of your callback function object is to

pass as your callback a one-line function that invokes a method in your application

package to actually do the work.

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