Reacting to field value changes

This section describes the purpose of the ON CHANGE interaction block.

The ON CHANGE interaction block can be used in different ways:
  • With form fields allowing only entire value input such as CHECKBOX, or using an additional widget such as a calendar in a DATEEDIT: ON CHANGE can be used to detect an immediate value change, or the selection of a value in the additional widget, without leaving the field.
  • With text fields like EDIT (allowing incomplete values), defined with the COMPLETER attribute to implement autocompletion: In this case the ON CHANGE trigger is used to fill the list of matching values, when the user types characters in (ON CHANGE is fired after a short delay).
  • With text fields like EDIT (allowing incomplete values): ON CHANGE can be used to detect a value change, when the field is left.

A typically usage of ON CHANGE is for example with a CHECKBOX, to enable/disable other form elements depending on the value of the checkbox field:

INPUT BY NAME rec.* ...
    ON CHANGE input_details -- can be TRUE or FALSE
       CALL DIALOG.setFieldActive("address1", rec.input_details)
       CALL DIALOG.setFieldActive("address2", rec.input_details)

The dialogtouched predefined action can also be used to detect field changes immediately, but with this action you cannot get the data in the target variables. Use of this special action is only recommended to detect if the user has started to modify data in the current dialog.