The dynamic dialog event loop

Dialog trigger identification

The code implementing dynamic dialogs must be generic. Triggers like ON ACTION myaction are identified as a simple string.

Implicit standard triggers

Standard dialog triggers such as BEFORE INPUT, BEFORE FIELD field-name, AFTER ROW do not need to be added when creating a dynamic dialog: These triggers are implicitly declared. To see a reaction to standard triggers, add a test for the trigger in the event loop.

Adding user-defined triggers

Dynamic dialogs can be configured with user-defined triggers, for example to execute code when a specific action is fired.

DEFINE d ui.Dialog
...
CALL d.addTrigger("ON ACTION print")
CALL d.addTrigger("ON DELETE")
...

Note that some triggers must be identified with the user-defined action name, as in "ON ACTION print".

User-defined triggers will then be handled in the dynamic dialog loop, when the event occurs.

Handling dialog events

To implement the "body" of a dynamic dialog, mix a WHILE loop with the ui.Dialog.nextEvent() method, to handle dialog events.

The WHILE loop will act as the main event handler of your dynamic dialog, and will loop, waiting for dialog events until you explicitly exit the loop with an EXIT WHILE instruction.

The nextEvent() method can return NULL in case of dialog error or when the dialog is terminated.

DEFINE d ui.Dialog,
       t STRING
...
WHILE (t := d.nextEvent()) IS NOT NULL
    CASE t
       WHEN "BEFORE DISPLAY"
          ...
       WHEN "ON ACTION print"
          ...
       WHEN "ON DELETE"
          ...
       WHEN "AFTER DISPLAY"
          ...
END WHILE

The standard triggers such as "BEFORE ROW" and "AFTER FIELD field-name" are equivalent to the trigger found in static dialog control blocks. These allow you to control the behavior of the dynamic dialog.

The ui.Dialog.nextEvent() only provides basic information about the event that occurred. For example, with BEFORE FIELD events only the field name is part of the string returned by nextEvent(). Use the ui.Dialog.getEventDescription() method to get detailed information about the last event.

The user-defined triggers that have been added with the addTrigger() method must also be handled in the dynamic dialog loop.

 ...
 WHEN "ON ACTION jump"
   CALL d.nextField("customer.cust_name")
 ...

 ...
 WHEN "AFTER FIELD cust_name"
   IF LENGTH(d.getFieldValue("customer.cust_name")) < 3 THEN
      ERROR "Customer name is too short"
      CALL d.nextField("customer.cust_name")
 END IF
 ...

For more details, see the ui.Dialog.nextEvent() method reference.