Object Oriented Programming in ABAP - Event with event handler method in different class

• Class C1 contains an event E1, for which the triggering method is T1.
• Event handler method for event E1 is M1, placed in the another class,C2.
• Registration is done at runtime for M1.
• Object is created from class C1 and the triggering method T1 is called, which raises the event and ultimately calls event handler method M1 in class C2.

REPORT zstp_oo_abap.

CLASS c1 DEFINITION.
  PUBLIC SECTION.
* Creating event : E1
    EVENTS: e1.
* Triggering method : T1
    METHODS : t1.
ENDCLASS.

CLASS c2 DEFINITION.
  PUBLIC SECTION.
*  Creating an event handling method.
    METHODS: m1 FOR EVENT e1 OF  c1.
ENDCLASS.

CLASS c1 IMPLEMENTATION.
* Method : T1 will raise the event
  METHOD : t1.
    WRITE:/5 'I am T1, going to raise event E1'.
    RAISE EVENT e1.
  ENDMETHOD.
ENDCLASS.

CLASS c2 IMPLEMENTATION.
* Method : M1 will be called when the event is raised
  METHOD : m1.
    WRITE:/5 ' I am the event handler method in c2'.
  ENDMETHOD.
ENDCLASS.

START-OF-SELECTION.
  DATA: oref1 TYPE REF TO c1,
        oref2 TYPE REF TO c2.
  CREATE OBJECT: oref1 , oref2  .
* Registering the event handler method
  SET HANDLER oref2->m1 FOR oref1  .
* Calling the event which will raise the event.
  CALL METHOD oref1->t1.

Output-

More than one Event Handler method can exist for same event

For an event in a class, there can be more than one event handler methods in same or different class. However, at runtime only one event handler method will be triggered at a time, based on the registration.

• Class C1 contains an event E1, for which the triggering method is T1 and the event handler methods are :-
  • M1 in same class C1.
  • M2 in another class C2.
• In the START-OF-SELECTION block, objects are created from class C1 and C2.
• First, registration is made using method M1 of class C1 as event handler method.
• Then, the event E1 is raised, calling method T1. This raises event handler method M1 of class C1.
• After that, the earlier registration is de-activated and new registration is made for method M2 of class C2 as event handler method .
• Event E1 is raised calling method T1. This raises event handler method M2 of class C2.

REPORT zstp_oo_abap.

CLASS c1 DEFINITION.
  PUBLIC SECTION.
* Creating event : E1
    EVENTS: e1.
*  Creating an event handling method.
    METHODS: m1 FOR EVENT e1 OF  c1.
* Method to raise the event
    METHODS : t1.
ENDCLASS.

CLASS c2 DEFINITION.
  PUBLIC SECTION.
*  Creating an event handling method.
    METHODS: m2 FOR EVENT e1 OF  c1.
ENDCLASS.

CLASS c1 IMPLEMENTATION.
* Method : T1 will raise the event
  METHOD : t1.
    WRITE:/5 'I am T1, going to raise event E1'.
    RAISE EVENT e1.
  ENDMETHOD.
* Method : M1 will be called when the event is raised
  METHOD : m1.
    WRITE:/5 ' I am the event handler method M1 in c1'.
  ENDMETHOD.
ENDCLASS.

CLASS c2 IMPLEMENTATION.
* Method : M2 will be called when the event is raised
  METHOD : m2.
    WRITE:/5 ' I am the event handler method M2 in c2'.
  ENDMETHOD.
ENDCLASS.

START-OF-SELECTION.
  DATA: oref1 TYPE REF TO c1,
        oref2 TYPE REF TO c2.
  CREATE OBJECT: oref1 , oref2  .
* Registering the event handler method
  SET HANDLER oref1->m1 FOR oref1  .
* Calling the event which will raise the event.
  CALL METHOD oref1->t1.
* De-Registering the earlier event handler method
  SET HANDLER oref1->m1 FOR oref1 ACTIVATION space .
* Registering the new event handler method
  SET HANDLER oref2->m2 FOR oref1  .
* Calling the event which will raise the event.
  CALL METHOD oref1->t1.

Output -