Drop down list box can be created in a dialog screen(SE51) as well as
The sap list box allows to select a value from the list but we cannot enter our own value in the list box
.The value list that will be displayed consists of two
fields TEXT field of TYPE 80(C) and internal KEY field of TYPE
In screen painter to create a input/output field into list box we use
'L" as a value for dropdown attribute for the i/o field.
In screen painter to determine the type of method that will be used to fill the value
list we use the attribute value list.
If it is blank the value list will be filled by the first column of the input help assigned
to the screen field.This input help can be defined in the ABAP Dictionary, on screen using SELECT,VALUES
screen statements or in event POV (PROCESS ON VALUE-REQUEST ) and the input help that
will be passed to the field should consists of 2 columns ,the key column is filled automatically by the system.SAP recommends value
list field should be blank.
The value can be 'A' meaning that the value list will be filled in the event PBO(PROCESS BEFORE OUTPUT) or before the screen is displayed.In this method we use function module VRM_SET_VALUES to fill the values and pass it to the i/o field.
If a function code is attached to the list box the selection of a value triggers a PAI
otherwise PAI will not trigger.