Apple Newton Utilities Guide de l'utilisateur télécharger pdf (Page 906)

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APPENDIX

A-2 Run-Time Results

Note

Protos built into the system use an analogous slot called

allocateContext, that holds the same thing as

stepAllocateContext. The allocateContext slot is for

declared children from the

viewChildren array and the

stepAllocateContext slot is for declared children from the

stepChildren array. ◆

Also, as a result of the declare operation, NTK creates a slot in the Display template

called

preallocatedContext. This slot holds a symbol that is the name of the

template, in this case

'Display. This symbol will be used by the system when the

view is instantiated to ﬁnd the preallocated view memory object for the Display view.

Run-Time Results 26

When the Calculator view is opened (even before its ViewSetupFormScript

method is executed), a view memory object is preallocated for each view declared

in Calculator. (The information required to do this is obtained from the

allocateContext and stepAllocateContext slots.) In our example, a view

memory object is created for the Display view.

The

Display slot in the Calculator view is updated so that it points to the newly

allocated Display view object.

Later in the instantiation process for the Calculator view, its child views are created

and shown, including the Display view. At this time, the view system looks at the

template for the Display view, sees the

preallocatedContext slot, and knows

that a view memory object has been preallocated for this view. Using this slot, the

system can ﬁnd the preallocated view.

The value of the

preallocatedContext slot is the name of another slot in the

Calculator view. The system locates this slot in the Calculator view, and ﬁnds there

a reference to the preallocated view object. Instead of creating a new view object

for the Display view, the system uses the preallocated view.

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Apple Newton Utilities Guide de l'utilisateur Page 906

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