Apple WebObjects 3.5 - Manual (Page 35)

Server-Side Dynamic Elements
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Finally, the WOString element defines a value attribute, which specifies the
string you want displayed. This value attribute is bound to the currentOption
variable, which is also bound to the item attribute of the WORepetition. As
you’ll recall, currentOption is updated with each iteration that the
WORepetition makes. So, for each item in the allOptions array (assigned to the
WORepetition’s list attribute), the WORepetition updates the currentOption
variable to point to that item and then the WOString prints it on the page.
Binding Values to Dynamic Elements
In the CyberWind example, all of the dynamic elements are bound to
variables and methods from the component that contains them (the Main
component). It’s common to bind to variables and methods declared
directly in the current component; however, you can bind to any value that
the component can access.
This means, for instance, that you can bind to variables from the application
or session object because the WOComponent class declares two instance
variables,
application and session , which point to the current application and the
current session. Look at CyberWind’s Footer component in WebObjects
Builder. This component displays, among other information, the date and
time the CyberWind application was started.This date is stored in the
application object, not in the Footer component. The Footer component’s
.wod file contains this declaration:
UP_SINCE:WOString {value = application.upSince.description};
To retrieve a value from this binding, WebObjects uses key-value coding, a
standard interface for accessing an object’s properties either through
methods designed for that purpose or directly through its instance variables.
With key-value coding, WebObjects sends the same message
(
takeValue:forKey: , or takeValue in Java) to any object it is trying to access. Key-
value coding first attempts to access properties through accessor methods
based on the key’s name.
For example, to resolve the binding for the WOString element in the
Footer component using key-value coding, WebObjects performs the
following steps:
• It resolves the value for the application key by looking for a method named
application in the component object.
In this case, WOComponent (Component in Java) defines the application
method, which returns the WOApplication object (WebApplication in
Java).