Screens and Processing Blocks

ABAP programs consist of processing blocks, and can contain screens as components. Both processing blocks and screens are controlled by the ABAP runtime environment.

Executable programs, module pools, and function groups can contain and process the following screens:

• Screens

  Defined using the Screen Painter; can be combined into screen sequences; called using CALL SCREEN or a transaction code; processed in dialog modules of the corresponding ABAP program.

• Selection Screens

  Defined within an ABAP program; called by the runtime environment or using the CALL SELECTION-SCREEN statement; processed in event blocks of the corresponding ABAP program.

• Lists

  Defined within an ABAP program; called by the runtime environment; processed in event blocks of the corresponding ABAP program.

Class pools do not support screens at the moment. Subroutine pools cannot contain their own screens.

All ABAP programs are made up of processing blocks. You cannot nest processing blocks. When a program is executed, its processing blocks are called. All of the statements in an ABAP program, apart from its global data declarations, belong to a processing block.

ABAP contains the following processing blocks:

Dialog Modules

Defined between the MODULE...ENDMODULEstatements in executable programs, module pools and function groups; has no local data area and no parameter interface; called using the MODULEstatement in screen flow logic; processes screens.

Event Blocks

Defined by one of the event key words; no local data area and no parameter interface; reacts to events in the ABAP runtime environment. (Exceptions: AT SELECTION-SCREENand GET are implemented internally using subroutines, and have a local data area).

We differentiate between:

• Program constructor event

  LOAD-OF-PROGRAM

  Called once by the ABAP runtime environment directly after the program has been loaded into the internal session; has a similar role in executable programs, module pools, function groups and subroutine pools as constructors have in ABAP Objects

• Reporting events

  INITIALIZATION

  START-OF-SELECTION

  GET

  END-OF-SELECTION

  Called by the ABAP runtime environment while an executable program is executed in the predefined sequence; contain application logic for executable programs.

• Selection screen events

  AT SELECTION-SCREEN OUTPUT

  AT SELECTION-SCREEN ON VALUE-REQUEST

  AT SELECTION-SCREEN ON HELP-REQUEST

  AT SELECTION-SCREEN ON f

  AT SELECTION-SCREEN ON BLOCK

  AT SELECTION-SCREEN ON RADIOBUTTON GROUP

  AT SELECTION SCREEN

  AT SELECTION SCREEN ON END OF f

  Called by the ABAP runtime environment following a user action on a selection screen in executable programs, module pools, and function groups; process selection screens.

• List events

  TOP-OF-PAGE

  END-OF-PAGE

  AT LINE-SELECTION

  AT PFnn

  AT USER-COMMAND

  Called by the ABAP runtime environment while a list is being created or after a user action on a list in executable programs, module pools, and function groups; process lists.

Procedures

Procedures have a local data area and a parameter interface: The following procedures exist:

• Subroutines

  Defined by FORM -ENDFORM in any program except class pools; called using the PERFORM statement in any ABAP program.

• Function modules

  Defined by FUNCTION -ENDFUNCTION in function groups; called using CALL FUNCTION from any ABAP program.

• Methods

  Defined by METHOD - ENDMETHOD in global classes in a class pool, or in local classes in any program; called using CALL METHOD from any ABAP program for global classes, and, for local classes, from the program in which the class is defined.