Enabling autocompletion

Autocompletion allows a list of completion proposals to be displayed while the user is typing text into a field.

Introduction to autocompletion

Text input fields (like EDIT and BUTTONEDIT) can be defined with an autocompletion feature, by combining the COMPLETER form field attribute with program code providing the list of completion proposals in a dynamic array of strings, with the DIALOG.setCompleterItems() method, when the ON CHANGE trigger is fired for the autocompletion field.

Defining a form field for autocompletion

In order to enable autocompletion in a text form field, you must define the COMPLETER attribute:

EDIT f1 = FORMONLY.firstname, COMPLETER;

The COMPLETER attribute can be used for EDIT and BUTTONEDIT fields.

Providing the front-end with a list of completion proposals

The DIALOG.setCompleterItems() method must be used to provide the list of completion proposals during dialog execution:

DEFINE items DYNAMIC ARRAY OF STRING
-- fill the array with items
LET items[1] = "Ann"
LET items[2] = "Anna"
LET items[3] = "Annabel"
CALL DIALOG.setCompleterItems(items)

Important: Consider the execution time of the code creating the completion proposal list. For example, avoid long complex SQL queries that can take more than a few milliseconds to complete.

The setCompleterItems() method will raise error -8114 if the list of items contains more than 50 elements. The purpose of autocompletion is to provide a short list of completion proposals to the user. Note that this error is not trappable with exception handlers like TRY/CATCH, the code must avoid exceeding the limit.

Detecting user input

When implementing autocompletion, you must detect when the user modifies the field value, to adapt the list of items with the setCompleterItems() method.

In order to detect user input, define the ON CHANGE dialog control block, and call a custom function by passing the DIALOG object, and the value of the current field as parameter, to filter the completion proposal list accordingly:

INPUT BY NAME rec.firstname
   ...
   ON CHANGE firstname
      CALL fill_proposals_firstname(DIALOG, rec.firstname)

For text fields defined with the COMPLETER attribute, the ON CHANGE trigger will be fired without leaving the field, each time the user types characters in. The event is fired after a short delay, to not overload the UI exchanges between the front-end and the runtime system.

Note: The item list for a field implementing autocompletion is not permanent: The program must re-define the autocompletion item list with setCompleterItems(), on every ON CHANGE event.

Example

The example below implements form field with autocompletion: Each time the ON CHANGE trigger is fired, the set of completion proposals is adapted to the current field value, to match names that start with the same characters typed by the user.

Form file (compl.per):

LAYOUT
GRID
{
[f1                             ]
[f2                             ]
}
END
END
ATTRIBUTES
EDIT f1 = FORMONLY.field1, COMPLETER;
EDIT f2 = FORMONLY.field2;
END

Program file (compl.4gl):

DEFINE all_names DYNAMIC ARRAY OF STRING

MAIN
  DEFINE rec RECORD
             field1 STRING,
             field2 STRING
         END RECORD
  CALL fill_names()
  OPEN FORM f FROM "compl"
  DISPLAY FORM f
  OPTIONS INPUT WRAP
  INPUT BY NAME rec.* ATTRIBUTES(UNBUFFERED)
      ON CHANGE field1
         CALL fill_proposals(DIALOG, rec.field1)
  END INPUT
END MAIN

FUNCTION fill_names()
  DEFINE i INTEGER
  LET i=0
  LET all_names[i:=i+1] = "Amanda"
  LET all_names[i:=i+1] = "Ann"
  LET all_names[i:=i+1] = "Anna"
  LET all_names[i:=i+1] = "Annabelle"
  LET all_names[i:=i+1] = "Barbara"
  LET all_names[i:=i+1] = "Barry"
  LET all_names[i:=i+1] = "Brice"
END FUNCTION

FUNCTION fill_proposals(dlg, curr_val)
  DEFINE dlg ui.Dialog, curr_val STRING
  DEFINE curr_set DYNAMIC ARRAY OF STRING,
         i, x INTEGER
  LET x=0
  FOR i=1 TO all_names.getLength()
      IF upshift(all_names[i]) MATCHES upshift(curr_val)||"*" THEN
         LET curr_set[x:=x+1] = all_names[i]
      END IF
  END FOR
  CALL dlg.setCompleterItems(curr_set)
END FUNCTION