Recognition: Advanced Topics

Using Advanced Topics in Recognition

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

or

recConfig

slot affects that view only.

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.