OOPS ABAP: EVENTS with Example

Events: Method of one class can call the method of another class.

Triggering Method:  This method raises the event.

Event Handler Method: The method will handle the event.

Register the event handler method using SET HANDLER statement.

CLASS class1.

METHOD DISPLAY

ENDCLASS.

---------------------------------------

CLASS CLASS2.

METHOD MESSAGE.

ENDCLASS.

Syntax for event handler:

SET HANDLER lo_object1 -> event_handler for lo_object2.

where lo_object1 -> class object in which event handler method is defined.

             EVENT_HANDLER -> Event handler method name.

             lo_object2 -> class object in which triggering method is defined.

 Example

*&---------------------------------------------------------------------*
*& Report ZVB_EVENTS
*&---------------------------------------------------------------------*
*&
*&---------------------------------------------------------------------*
REPORT zvb_events.

PARAMETERS: p_vbeln TYPE vbeln_va.

DATA:it_vbak TYPE ztt_vbak,  "Table type
     is_vbak TYPE zst_vbak. "Global structure

CLASS class1 DEFINITION.
  PUBLIC SECTION.
    METHODS display IMPORTING pp_vbeln TYPE vbeln_va
                    EXPORTING pt_vbak  TYPE ztt_vbak. "Table type

    EVENTS: no_input.
ENDCLASS.
CLASS class1 IMPLEMENTATION.
  METHOD display.                   "Triggering method
    IF pp_vbeln IS INITIAL.
      RAISE EVENT no_input.
    ELSE.
      SELECT vbeln erdat erzet
        FROM vbak
        INTO TABLE pt_vbak
        WHERE vbeln = pp_vbeln.
    ENDIF.
  ENDMETHOD.
ENDCLASS.

CLASS class2 DEFINITION.
  PUBLIC SECTION.
    METHODS message FOR EVENT no_input OF class1.
ENDCLASS.
CLASS class2 IMPLEMENTATION.
  METHOD message.                   " Event handler method
    WRITE: 'No data avilable for the input'.
  ENDMETHOD.
ENDCLASS.

START-OF-SELECTION.
  DATA:lo_object1 TYPE REF TO class1,
       lo_object2 TYPE REF TO class2.

  CREATE OBJECT lo_object1.
  CREATE OBJECT lo_object2.

*Registering the event handler method
  SET HANDLER lo_object2->message FOR lo_object1.
  lo_object1->display( EXPORTING
                          pp_vbeln = p_vbeln
                       IMPORTING
                          pt_vbak = it_vbak ).

  IF it_vbak IS NOT INITIAL.
    LOOP AT it_vbak INTO is_vbak.
      WRITE: / is_vbak-vbeln,
              10 is_vbak-erdat,
              25 is_vbak-erzet.
    ENDLOOP.
  ENDIF. 

Output: 

1. If p_vbeln is initial.