FAQ's - APPX Software, Inc. : APPX Utility : APPX Development Environment : Input Processes :
What’s PreDisplay/Verify for?
|There are three event points which complement each other in order to provide
the flexibility actually needed when designing a well behaved, complex input
process. We will ignore the OPTION INTERCEPT event point (and others) for the
purposes of this discussion. They are:
PRE-DISPLAY PRE-DISPLAY/VERIFY VERIFY
VERIFY is executed after the operator keys data and presses ENTER. It is not executed prior to displaying the screen. It is only executed after data entry. The this event point's purpose to validate data entered and to allow for displaying of ERROR and WARNING messages..
PRE-DISPLAY is executed only once when a record is initially retrieved in Change mode or Inquire mode, just before the screen is displayed. In Add mode it is executed once for each ENTRY LEVEL which occurs, just before the screen is displayed.
Pre-Display's primary purpose is to allow default values to be set, and screen attributes such as NO INPUT, etc.
The PRE-DISPLAY/VERIFY event point is the most difficult to understand because it is more or less a combination of the other two event points although there are some differences. It is executed before the screen is displayed after retrieving a record (much like PRE-DISPLAY).
However, it is also executed after data entry - after the VERIFY event point - just before the screen is redisplayed. It can be executed multiple times for a record being processed, not just once like PRE-DISPLAY. This is intended to facilitate displaying of related information such as data lookups, results of calculations, etc.
This event point should not be used to validate data unless the ERROR and WARNING messages are intended to be displayed when the screen is initially displayed since they will be executed at that point as well. This behavior is the source of the current discussion regarding error messages which display in inquire mode as well as other modes.
It is my contention that the prior behavior (before 3.3) of APPX was the correct one and there is a good chance that the next release (3.4) will revert back to that behavior.
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