The AT SELECTION-SCREEN event is triggered in the PAI of the selection screen once the ABAP runtime environment has passed all of the input data from the selection screen to the ABAP program. If an error message occurs in this processing block, the selection screen is redisplayed with all of its fields ready for input. This allows you to check input values for consistency.
The following executable program is connected to the logical database F1S.
REPORT demo_at_selection_screen . NODES spfli. AT SELECTION-SCREEN. IF carrid-low IS INITIAL OR airp_fr-low IS INITIAL OR airp_to-low IS INITIAL. MESSAGE e888(sabapdocu) WITH text-001. ENDIF.
If the user does not enter values in all of the fields on the selection screen, an error message appears in the status line. This makes all of the input fields mandatory, even though they are not defined as such in the logical database.