Both the events AT SELECTION-SCREEN and AT USER-COMMAND are processed after user input. Then what is the difference between these and when we should use what?
At selection screen is used to validate the fields in a selection screen...and at user command is used to modify the screen in a selection screen and in genarating secondary lists..
OR
AT SELECTION-SCREEN is used where you have a seperate selection screen using select-options or parameters where as AT USER-COMMAND is used where no selection screen exists....at.user-command is mainly used while setting pf-status which means creating our own menu with function codes etc...