Why do we use these design patterns
The delegation design pattern and the event handling design pattern provide loose coupling communication between objects.
When to use the delegation design pattern
- You need bi-directional communication between objects
- You need to know if there is a delegate that handles the communication
When to use the event handling design pattern
- You need a very flexible one way communication where every object can attach himself to the event.
How to implement the delegation design pattern
- Create an interface for the delegate
- Implement the interface
- Set your object as the delegate
How to implement the event handling design pattern
- Create an event handler method
- Attach the event handler method to the event
In practice
Okay we have talked enough theoretically. I have created an example which implements both design patterns.
The example has only one object of an person and you can have two confirmations:
- Confirm the name
- Confirm to save
The name confirmation implements the delegation design pattern.
The save confirmation implements the event handling design pattern.
UML
Source of the example
|
REPORT zz_rv_test. PARAMETERS p_name TYPE text20 ##sel_wrong.
* CLASS lcl_confirm_save DEFINITION *———————————————————————-* CLASS lcl_confirm_save DEFINITION FINAL. PUBLIC SECTION. METHODS show_confirmation. EVENTS evt_save. PRIVATE SECTION. DATA mv_answer TYPE char1. CONSTANTS gc_confirm_save TYPE text40 VALUE ‘Do you want to save?’ ##no_text. ENDCLASS. “lcl_confirm_save DEFINITION
* CLASS lcl_confirm_save IMPLEMENTATION *———————————————————————-* CLASS lcl_confirm_save IMPLEMENTATION. METHOD show_confirmation. CALL FUNCTION ‘POPUP_TO_CONFIRM’ EXPORTING text_question = gc_confirm_save IMPORTING answer = mv_answer EXCEPTIONS OTHERS = 1. IF sy-subrc = 0 AND mv_answer = ‘1’. RAISE EVENT evt_save. ENDIF. ENDMETHOD. “show_confirmation ENDCLASS. “lcl_confirm_save IMPLEMENTATION
* INTERFACE zif_confirm_name_delegate *———————————————————————-* INTERFACE zif_confirm_name_delegate. METHODS get_name RETURNING value(rv_name) TYPE char20. METHODS handle_confirmed. ENDINTERFACE. “zif_confirm_name_delegate *———————————————————————-* * CLASS lcl_confirm_name DEFINITION *———————————————————————-* CLASS lcl_confirm_name DEFINITION FINAL. PUBLIC SECTION. METHODS constructor IMPORTING io_delegate TYPE REF TO zif_confirm_name_delegate. METHODS show_confirmation. PRIVATE SECTION. DATA mv_answer TYPE char1. DATA mo_delegate TYPE REF TO zif_confirm_name_delegate. CONSTANTS gc_confirm_name TYPE text40 VALUE ‘Is your name:‘ ##no_text. ENDCLASS. “lcl_confirm_name DEFINITION *———————————————————————-* * CLASS lcl_confirm_name IMPLEMENTATION *———————————————————————-* CLASS lcl_confirm_name IMPLEMENTATION. METHOD constructor. “IF mo_delegate IS NOT BOUND. “Raise exception “ENDIF. mo_delegate = io_delegate. ENDMETHOD. “constructor METHOD show_confirmation. DATA lv_confirm TYPE text40. lv_confirm = gc_confirm_name && ` ` && mo_delegate->get_name( ). CALL FUNCTION ‘POPUP_TO_CONFIRM’ EXPORTING text_question = lv_confirm IMPORTING answer = mv_answer EXCEPTIONS OTHERS = 1. IF sy-subrc = 0 AND mv_answer = ‘1’. mo_delegate->handle_confirmed( ). ENDIF. ENDMETHOD. “show_confirmation ENDCLASS. “lcl_confirm_name IMPLEMENTATION *———————————————————————-* * CLASS LCL_PERSON DEFINITION *———————————————————————-* CLASS lcl_person DEFINITION FINAL. PUBLIC SECTION. INTERFACES zif_confirm_name_delegate. METHODS constructor IMPORTING iv_name TYPE char20. METHODS confirm_my_name. METHODS save. PRIVATE SECTION. METHODS handle_save FOR EVENT evt_save OF lcl_confirm_save. DATA mv_name TYPE char20. ENDCLASS. “LCL_PERSON DEFINITION *———————————————————————-* * CLASS LCL_PERSON IMPLEMENTATION *———————————————————————-* CLASS lcl_person IMPLEMENTATION. METHOD constructor. mv_name = iv_name. ENDMETHOD. “constructor METHOD confirm_my_name. DATA lo_confirm TYPE REF TO lcl_confirm_name. CREATE OBJECT lo_confirm EXPORTING io_delegate = me. lo_confirm->show_confirmation( ). ENDMETHOD. “CONFIRM_my_name METHOD save. DATA lo_confirm TYPE REF TO lcl_confirm_save. CREATE OBJECT lo_confirm. SET HANDLER handle_save FOR lo_confirm ACTIVATION abap_true. lo_confirm->show_confirmation( ). SET HANDLER handle_save FOR lo_confirm ACTIVATION abap_false. ENDMETHOD. “save METHOD handle_save. WRITE: / ‘SAVED:‘, mv_name. ENDMETHOD. “handle_save METHOD zif_confirm_name_delegate~get_name. rv_name = mv_name. ENDMETHOD. “zif_confirm_name_delegate~get_name METHOD zif_confirm_name_delegate~handle_confirmed. WRITE: / ‘CONFIRMED:‘, mv_name. ENDMETHOD. “zif_confirm_name_delegate~handle_confirmed ENDCLASS. “LCL_PERSON IMPLEMENTATION *———————————————————————-* * CLASS lcl_main_ctr DEFINITION *———————————————————————-* CLASS lcl_main_ctr DEFINITION FINAL CREATE PRIVATE. PUBLIC SECTION. CLASS-METHODS class_constructor. METHODS process. CLASS-DATA so_main_ctr TYPE REF TO lcl_main_ctr. ENDCLASS. “lcl_main_ctr DEFINITION *———————————————————————-* * CLASS lcl_main_ctr IMPLEMENTATION *———————————————————————-* CLASS lcl_main_ctr IMPLEMENTATION. METHOD class_constructor. CREATE OBJECT so_main_ctr. ENDMETHOD. “class_constructor METHOD process. DATA lo_person TYPE REF TO lcl_person. CREATE OBJECT lo_person EXPORTING iv_name = p_name. lo_person->confirm_my_name( ). lo_person->save( ). WRITE: / space. ENDMETHOD. “process ENDCLASS. “lcl_main_ctr IMPLEMENTATION *——————————————————————–* * Start of selection *——————————————————————–* START-OF-SELECTION. lcl_main_ctr=>so_main_ctr->process( ). |
Please let me know if you have any questions.
Regards,