Apple Newton Utilities User's Guide download pdf (Page 111)

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CHAPTER 3

Views

About Views 3-27

Declaring a View 3

Before diving into the discussion of view instantiation, it is important to understand

the term declaring. Declaring a view is something you do during the application

development process using the Newton Toolkit (NTK). Declaring a view allows it

to be accessed symbolically from another view.

In NTK, you declare a view using the Template Info command. (Although the

phrase “declaring a view” is being used here, at development time, you’re really

just dealing with the view template.) In the Template Info dialog, you declare a

view by checking the box entitled “Declare To,” and then choosing another view in

which to declare the selected view. The name you give your view must be a valid

symbol, and not a reserved word or the name of a system method.

You always declare a view in its parent or in some other view farther up the parent

chain. It’s best, for efﬁciency and speed, to declare a view in the lowest level

possible in the view hierarchy; that is, in its parent view or as close to it as possible.

If you declare a view in a view other than the parent view, it may get the wrong

parent view. Because the view’s parent is wrong, its coordinates will be wrong as

well, so it will show up at the wrong position on screen.

Declaring a view simply puts the declared view in the named slot. See Appendix A,

“The Inside Story on Declare,” for a complete description. The slot name is the

name of the view you are declaring. The slot value, at run time, will hold a

reference to the declared view.

The base view of your application is always declared in the system root view. Note

that the application base view is declared in a slot named with its application symbol,

speciﬁed in the Application Symbol ﬁeld of the Project Settings slip in NTK.

Why would you want to declare a view? When a view is declared in another view,

it can be accessed symbolically from that other view. The NewtonScript inheritance

rules already allow access from a view to its parent view, but there is no direct

access from a parent view to its child views, or between child views of a common

parent. Declaring a view provides this access.

For example, if you have two child views of a common parent, and they need to

send messages to each other, you need to declare each of them in the common

parent view. Or, if a parent view needs to send messages to one of its child views,

the child view must be declared in the parent view.

One key situation requiring a declared view is when you want to send the

Open

message to show a nonvisible view. The

Open message can only be sent to a

declared view.

Declaring a view has a small amount of system overhead associated with it. This is

why the system doesn’t just automatically declare every view you create. You

should only declare views that you need to access from other views.

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