There is no mandatory event in a report program. Events are actually used to organize the statements and control the flow of the program. If the program contains no explicitly defined event blocks, all the statements in the program form the entire event block START-OF-SELECTION. ABAP runtime environment automatically introduces a START-OF-SELECTION at the first execution line.
ABAP/4 report programs are event driven programs. Following events are triggered in a report.
LOAD OF PROGRAM. - If propgram is of type 1, M, F, or S; then LOAD-OF-PROGRAM is trigerred first and then INITIALIZATION. The purpose of load of program is to load the program into system memory so that the program can be executed.
INITIALIZATION. - just once.
AT SELECTION-SCREEN OUTPUT. - when there is selection-screen
AT SELECTION-SCREEN. - when user interacts.
START-OF-SELECTION. - when F8.This is the default event in ABAP.
END-OF-SELECTION. - At the end
EVENTS IN A CLASSICAL REPORT:
1. INITIALIZATION: This is triggered when the report is loaded in memory.
2. AT SELECTION-SCREEN OUTPUT: This is triggered when the selection screen is loaded in memory before being displayed.
3. AT SELECTION-SCREEN/<field> : This event is triggered before leaving the selection screen.
4. START-OF-SELECTION: This is the the first and default event for displaying the report. Data retrieval logic is written under this event.
OUTPUT EVENT(5, 6):
5. TOP-OF-PAGE: This event is triggered every time a new page is started in the list.
6. END-OF-PAGE : This event is triggered every time the list data reaches the footer region of the page.
7. END-OF-SELECTION: This event is triggered after the START-OF-SELECTION is completed.
This event is used when there is use of logical data base in the report. It is triggered in type 1 programs once the logical database completes reading all data i.e. all the selection is finished and before the list processor is started. This statement tells the server that all the database reading is completed and no more data reading is going to take place. END-OF-SELECTION is generally used for the summary/results of reports. In an executable program without logical data base, there is no need to implement the event block END-OF-SELECTION.
After a program is executed by the user, the database is locked when it encounters a START-OF-SELECTION statement and the lock is released when an END-OF-SELECTION statement is encountered (to maintain the consistency). Data selection is done between START-OF-SELECTION and END-OF-SELECTION. Now if we don’t write the END-OF-SELECTION statement, the database will remain locked till the programs get terminated. Hence, the performance will be reduced. So it is always good practice to write END-OF-SELECTION statement after finishing the data selection from database.
EVENTS IN AN INTERACTIVE REPORT:
In addition of the above, the following events are possible in case of Interactive Reports.
1. Top of page during line selection : top of page event for secondary list.
2. At line-selection : evey time user dbl-clicks(F2) on the list data.
3. At pF<key> : function key from F5 to F12 to perform interactive action on the list.
4. At user-command.
==================================================
Finally I want to include one point:
If you debug your report program from the Abap editor screen then it triggers from
1.Initialization,
2.At Selection-screen,
3.Start-of Selection,
4.End-of Selection,
5.Top-of-page,
6.End-of-page.
But if you debug from the selection-screen then it triggers from
1.At Selection-Screen,
2.Start-of-selection,
3.Top-of-page,
4.End-of-page.