Apple WebObjects 3.5 Manuale Utente Scaricare il pdf (Pagina 172)

Chapter 10 The WebScript Language

172

automatically deﬁnes two accessor methods: one to retrieve the instance

variable’s value, and one to change the value.

For example, the

Application.wos script in the Visitors example declares this

instance variable, which keeps track of the number of visitors:

id visitorNum;

When WebScript parses this ﬁle, it sees this declaration and implicitly deﬁnes

two methods that work like this:

- visitorNum {

return visitorNum;

}

- setVisitorNum:newValue {

visitorNum = newValue;

}

(You don’t see these methods in the script ﬁle.) The Main.wos script access the

application’s

visitorNum variable using these statements:

number = [[self application] visitorNum];

...

[[self application] setVisitorNum:number];

Note: self is a keyword that represents the current object. For more information,

see “Reserved Words” (page 178).

You can also access an instance variable declared in one component script from

another component script. This is something you commonly do right before you

navigate to a new page, for example:

id anotherPage = [[self application] pageWithName:@"Hello"];

[anotherPage setNameString:newValue];

The current script uses the statement [anotherPage setNameString:newValue];

to set the value of

nameString, which is declared in the page named Hello.

Sending a Message to a Class

Usually, the object receiving a message is an instance of a class. For example, in

this statement the variable

aString is an instance of the class NSString:

[aString length];

You can also send messages to a class. You send a class a message when you want

to create a new instance of that class. For example this statement tells the class

NSString to invoke its

stringWithString: method, which returns an instance

of NSString that contains the speciﬁed string:

1 2 ... 167 168 169 170 171 172 173 174 175 176 177 ... 217 218

Nessun commento

Apple WebObjects 3.5 Manuale Utente Pagina 172