What are events In a screen

Question

What are events In a screen
could u plz explain clearly

Answer 1

Hello
the events of the screen are
Variants:
1.PROCESS BEFORE OUTPUT. Process before output
2.PROCESS AFTER INPUT. Process after user input
3.PROCESS ON HELP-REQUEST. User-programmed F1 help
4.PROCESS ON VALUE-REQUEST. User-programmer F4 help
Variant 1
PROCESS BEFORE OUTPUT.
Effect
Processing before the screen is displayed (PBO).
Examples
Initializing screen fields, inserting default values, positioning the cursor, showing and hiding fields and changing field attributes dynamically.
Variant 2
PROCESS AFTER INPUT.
Effect
Processing after user input.
Examples
Checking values where there is no automatic check, processing the cursor position, processing correct entries or triggering an error dialog.
Variant 3
PROCESS ON HELP-REQUEST.
Effect
POH event for user-programmed help. Modules in this event are processed when the user presses F1 with the cursor positioned on a screen field. In the subsequent FIELD statements, you can specify a data element supplement (or determine one in an application module). The texts are then displayed by the help system.
Examples
FIELD XY WITH '0001'.
Displays data element addition 0001 for field XY.
FIELD XY WITH variable.
Displays the data element supplement with the number contained in variable for the field XY.
FIELD XY MODULE XYZ WITH variable .
The relevant data element supplement is determined in module XYZ, where it is placed in variable. Use this procedure whenever you cannot determine the correct data element supplement until the F1 event.
Variant 4
PROCESS ON VALUE-REQUEST.
Effect
Event in user-programmed help that occurs when the user presses F4 with the cursor positioned on a screen field. The modules specified in the subsequent FIELD statements are called instead of the SAP help system.
Example
FIELD XY MODULE XYZ
Module XYZ determines the value of field XY and places it in the input field on the screen.
Reward the points and close the thread.
Vasanth