ABAP Eventhandling (simple explained)
Events it’s a possibility of the classes to tell anyone who is interested in this, that some changes in the class was made.
Class _A don’t know anything about class _B or class _C. He just send the message for all listener. Like a radio station.
To make listener classes able to get events from the sender class, we must register this event. Like a radio station that you choose in the car to listen all interesting news.
Below you can see some example:
REPORT. CLASS _a DEFINITION. PUBLIC SECTION. METHODS change_price IMPORTING i_price TYPE price. EVENTS price_was_changed. PRIVATE SECTION. DATA price TYPE price. ENDCLASS. CLASS _a IMPLEMENTATION. METHOD change_price. price = i_price. RAISE EVENT price_was_changed. ENDMETHOD. ENDCLASS. CLASS _b DEFINITION. PUBLIC SECTION. METHODS handle_price_was_changed FOR EVENT price_was_changed OF _a. ENDCLASS. CLASS _b IMPLEMENTATION. METHOD handle_price_was_changed. WRITE: 'Gotcha!'. ENDMETHOD. ENDCLASS. CLASS _c DEFINITION. PUBLIC SECTION. METHODS handle_double_click FOR EVENT double_click OF cl_gui_alv_grid. ENDCLASS. CLASS _c IMPLEMENTATION. METHOD handle_double_click. WRITE `Dont't care about class _a events`. ENDMETHOD. ENDCLASS. START-OF-SELECTION. DATA(shop) = NEW _a( ). DATA(listener_b) = NEW _b( ). DATA(listener_c) = NEW _c( ). SET HANDLER listener_b->handle_price_was_changed FOR ALL INSTANCES. SET HANDLER listener_c->handle_double_click FOR ALL INSTANCES. shop->change_price( '10.99' ).
Result. After price was change price_was_changed event was raised. But because we set only one listener (listener_b) to this event, only one handler was triggered.
Nice explanation! 🙂 In addition to the radio comparison, directional radio is also possible. In this case, SET HANDLER registers handling for an event of a specific instance (see ABAP help).
Super nice explanation about event handling concept. It's really easy to understand with your vivid examples.
Thank you so much.