HP 3000 Manuals HP 3000 Manuals
Summary
It's important to understand the actions that occur during data screen
processing. A number of system items are available to help you make full
use of data screens, and make them operate efficiently for your users.
These system items are summarized below.
* *FIELDNO. A communication area field containing the number of
the current screen field. You can alter this value by moving a
new number to it with the MOVE logic command. Moving a value to
*FIELDNO alters the screen field processing sequence, allowing you
to branch to a field depending on the value of another.
* *NEWTIE. A communication area field that contains the number of
the next field to be processed. You can alter this value manually
using the TIE command, or by moving a new value to it with the
MOVE command. It differs from *FIELDNO in that it only takes
effect once all normal input processing for the field has
finished.
* *ENTERED. A read-only switch that enables you to determine when
a screen field function is being executed. *ENTERED is off before
data entry, and on after successful data entry.
* ERROR Messages. If an ERROR message is generated by a data
input validation test or by an after function, HP ALLBASE/4GL
automatically requests the user to correct the data entry and
commit the field again. This prevents the user committing invalid
data.
Data Movement
When HP ALLBASE/4GL first displays a field, it moves data to the internal
screen field buffer before it executes the field function. Data is not
displayed on the screen until the function finishes. This means you can
refer to the screen buffer contents and modify them with the function.
The modified data is displayed upon completion of the function.
HP ALLBASE/4GL executes the after function for a field before the data
movement for the field occurs. This means that the after function cannot
rely on having the values available in data movement destination fields.
However, the after function can access the value in the internal screen
field buffer, and if required, modify this value before the data movement
for the screen field occurs.
If any automatic data validation, or data validation in an after
function, results in an error, the normal data movement for the screen
field does not occur.