Apple Newton Utilities Podręcznik Użytkownika Pobierz pdf (Strona 393)

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CHAPTER 10

Recognition: Advanced Topics

Using Advanced Topics in Recognition 10-17

The PurgeAreaCache function causes the recognition system to adopt the

settings that the

recConfig frame speciﬁes. This function is explained in more

detail in the next section, “Changing Recognition Behavior Dynamically.”

Normally, you need not call the

PurgeAreaCache function when specifying a

recConfig frame as part of a view’s template. However, you must call this

function to change a

recConfig frame at run time. For example, the previous

code fragment calculates values determining the size and location of the grid view

according to the size of the enclosing parent view; thus, the parent view must

already exist before the grid view’s

recConfig frame can be constructed.

Therefore, the grid view’s

recConfig frame is constructed from within the

ViewSetupDoneScript method of the parent view that encloses the grid view.

At the time the

viewSetupDoneScript method is executed, the system has

already used the

recConfig frame supplied by the enclosing view’s template. In

order to cause the system to use the new

recConfig frame—the one that deﬁnes

the grid view—the

ViewSetupDoneScript method must call the

PurgeAreaCache function.

Changing Recognition Behavior Dynamically 10

To change a view’s recognition behavior dynamically, you must indicate the view’s

new conﬁguration (by setting view ﬂags, changing the view’s

dictionaries

slot, or deﬁning a

recConfig frame) and make the recognition system use the

new settings. The system supplies three functions that you can use to make the

system adopt new recognition settings; each is appropriate for a particular situation.

The function you use to adopt new settings depends on whether you are changing

the recognition behavior of all views or just changing the behavior of individual

views. Changes to user preferences for recognition affect the recognition behavior

of all views. On the other hand, changing the value of a single view’s

viewFlags

recConfig slot affects that view only.

Note

It is recommended that you do not change any user settings

without conﬁrmation from the user.

◆

To change the recognition behavior of a single view dynamically, use the global

function

SetValue to change the value of the view’s viewFlags slot or

recConfig slot. In addition to setting the new value, the SetValue function

invalidates the area cache, which is a buffer that stores a small number of

recognition areas. Your changes to recognition behavior are incorporated when the

recognition area for your view is rebuilt.

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