List box controls and selection box controls contain a number of items. Both the controls and the items are dialog elements; the controls are the parents of the items.
There are two ways of creating list box items and selection box items:
Use Natural code to create individual and multiple list box items dynamically; or
use the dialog editor (to add single or arrays of list box items and selection box items).
In Natural code, this may look like this:
#AMOUNT := 5 ITEM (1) := 'BERLIN' ITEM (2) := 'PARIS' ITEM (3) := 'LONDON' ITEM (4) := 'MILAN' ITEM (5) := 'MADRID' PROCESS GUI ACTION ADD-ITEMS WITH #LB-1 #AMOUNT #ITEM (1:5) GIVING #RESPONSE
You first specify the number of items you want to create, name the items,
and use the PROCESS GUI statement action
ADD-ITEMS.
If you want to go through all items of a
list box
control to find out which ones are selected, it is advisable to use
the SELECTED-SUCCESSOR
attribute because if a
list box
control contains a large number of items (100, for example), this
helps improve performance. If you use
SELECTED-SUCCESSOR, you
have one query instead of 100 individual queries if you use the attributes
SELECTED and
SUCCESSOR.
Example:
/* Displays the STRING attribute of every SELECTED list-box item
MOVE #LISTBOX.SELECTED-SUCCESSOR TO #LBITEM
REPEAT UNTIL #LBITEM = NULL-HANDLE
.../* STRING display logic
MOVE #LBITEM.SELECTED-SUCCESSOR TO #LBITEM
END-REPEAT
For performance reasons, you should not use the
SELECTED-SUCCESSOR
attribute to refer to the same dialog element handle twice, because Natural
goes through the list of item handles twice:
/* Displays the STRING attribute of every SELECTED list-box item,
/* but may be slow
MOVE #LISTBOX.SELECTED-SUCCESSOR TO #LBITEM
REPEAT UNTIL #LBITEM = NULL-HANDLE
IF #LBITEM.SELECTED-SUCCESSOR = NULL-HANDLE /* Searches in the list of items
IGNORE
END-IF
.../* STRING display logic
MOVE #LBITEM.SELECTED-SUCCESSOR TO #LBITEM /* Searches in the list of items
END-REPEAT /* for the second time
To avoid this problem, you use a second variable #OLDITEM
besides #LBITEM:
/* Displays the STRING attribute of every SELECTED list-box item
MOVE #LISTBOX.SELECTED-SUCCESSOR TO #LBITEM
REPEAT UNTIL #LBITEM = NULL-HANDLE
#OLDITEM = #LBITEM
#LBITEM = #LBITEM.SELECTED-SUCCESSOR/* Searches in the list of items (once)
IF #LBITEM = NULL-HANDLE
IGNORE
END-IF
.../* Display logic using #OLDITEM.STRING
END-REPEAT
If you retrieve the handle values of the selected items, a value other
than NULL-HANDLE would normally be returned by selected items.
Such a handle value can also be returned by non-selected items if you assign
SELECTED-SUCCESSOR a
value immediately before retrieving the
SELECTED-SUCCESSOR
value of a non-selected item, as shown in the following example:
... PTR := #LB-1.SELECTED-SUCCESSOR PTR := NOT_SELECTEDHANDLE.SELECTED-SUCCESSOR IF NOT_SELECTEDHANDLE.SELECTED-SUCCESSOR = NULL-HANDLE THEN #DLG$WINDOW.STATUS-TEXT := 'NULL-HANDLE' ELSE COMPRESS 'NEXT SELECTION: ' PTR.STRING TO #DLG$WINDOW.STATUS-TEXT END-IF ...
If you want to query whether a particular item in a
list box
control is selected, you get the best performance by using the
SELECTED attribute:
#DLG$WINDOW.STRING:= #LB-1-ITEMS.SELECTED(3)
To prevent an end user from typing in input data in a selection box control or input field control, you have several possiblities, for example:
setting the MODIFIABLE attribute to
FALSE for the dialog element, or
setting session parameter AD=P, or
using a control variable (CV).
If a selection box control is protected, it is still possible to select
items; only values from the item list will be displayed in its input field. If
the STRING attribute is set
to a value (dynamically or by initialisation) which is not in the item list,
the value will not be visible to the end user.
