Apple WebObjects 3.5 Uživatelský manuál stáhnout pdf (Strana 49)

Initialization and Deallocation Methods

Component Initialization

A component object’s init method is invoked when the component object is

created. Just how often a particular component object is created depends on

whether the application object is caching pages. For more information, see

“WebObjects Viewed Through Its Classes” (page 63). If page caching is

turned on (as it is by default), the application object generally creates the

component object once and then restores that object from the cache every

time it is involved in a user request. If page caching is turned off, the

component object is freed at the end of the request-response loop.

Note: The pageWithName: method shown in the section “Action Methods”

(page 43) always creates a new component object, even if page caching is

turned on.

A component object’s

init method usually initializes component variables.

For example, in the EmployeeBook example, the

Department.wos script uses

init to initialize the departments component variable:

// WebScript EmployeeBook Department.wos

id departments;

- init {

id departmentsPath;

[super init];

departmentsPath = [[self application]

pathForResourceNamed:@"Departments" ofType:@"array"];

departments = [NSArray arrayWithContentsOfFile:departmentsPath];

return self;

}

The component awake method is invoked immediately after the init method

and each time the component object is restored from the page cache. Just

as in

init, you can implement an awake method that initializes component

variables. For example, in the DodgeDemo application, the

Car.wos script

uses

awake to initialize the shoppingCart component variable:

// WebScript DodgeDemo Car.wos

- awake {

shoppingCart = [[self session] shoppingCart];

}

In general, you use init to initialize component instance variables instead of

awake. The reason is that init is invoked only at component initialization time,

whereas

awake is potentially invoked much more than that. If, however, you

want to minimize the amount of state stored between cycles of the request-

response loop, you might choose to initialize component instance variables

awake and then deallocate them in sleep (by setting them to nil in WebScript

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