Apple Newton Utilities User's Guide download pdf (Page 110)

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CHAPTER 3

Views

3-26 About Views

IMPORTANT

Remember that the viewChildren and stepChildren arrays

contain templates, not views. If you try to send a message like

Hide to one of the objects listed in this array, the system will

probably throw an exception because it is not a view.

During run time, if you want to obtain references to the child

views of a particular view, you must use the ChildViewFrames

method. This method returns views from both the

viewChildren and stepChildren slots. This method is

described in “Getting References to Views” (page 3-32).

▲

Application-Deﬁned Methods 3

As your application executes, it receives messages from the system that you can

choose to handle by providing methods that are named after the messages. These

messages give you a chance to perform your own processing as particular events

are occurring.

For example, with views, the system performs default initialization operations

when a view is instantiated. It also sends a view a

ViewSetupFormScript

message. If you provide a method to handle this message, you can perform your

own initialization operations in the method. However, handling system messages in

your application is optional.

The system usually performs its own actions to handle each event for which it

sends your view messages. Your system message-handling methods do not override

these system actions. You cannot change, delete, or substitute for the default system

event-handling actions. Your system message-handling methods augment the

system actions.

For example, when the view system receives a Show command for a view, it

displays the view. It also sends the view the

ViewShowScript message. If you

have provided a

ViewShowScript method, you can perform any special

processing that you need to do when the view is displayed.

The system sends messages to your application at speciﬁc times during its handling

of an event. Some messages are sent before the system does anything to respond to

the event, and some are sent after the system has already performed its actions. The

timing is explained in each of the message descriptions in “Application–Deﬁned

Methods” (page 2-65) in the Newton Programmer’s Reference.

View Instantiation 3

View instantiation refers to the act of creating a view from its template. The process

of view instantiation includes several steps and it is important to understand when

and in what order the steps occur.

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