Answer Posted / the abap

At selection screen is used to validate input..

at selection screen on output is used to set screen attributes

AT SELECTION_SCREEN OUTPUT
LOOP AT SCREEN.
if VIEW = 'X' " View radio button selects
IF SCREEN-NAME = 'PR1'.
screen-INPUT = 0.
modify screen.
ENDIF.
IF SCREEN-NAME = 'PR2'.
screen-INPUT = 0.
modify screen.
ENDIF.
ENDLOOP.
AT SELECTION-SCREEN.

*val....1 Variant check
* Once the user has entered variant, check about its existence
PERFORM CHECK_PVAR. "Using FM REUSE_ALV_VARIANT_EXISTENCE
*val....2 Sd do not exists
SELECT SINGLE VBELN INTO WA_HEADER-VBELN FROM VBAK WHERE VBELN IN
S_VBELN.
IF SY-SUBRC 0.
MESSAGE E010 WITH TEXT-010.
ENDIF.
*val.....3 Date of creation check
LOOP AT S_DOC.
IF S_DOC-LOW > SY-DATUM OR S_DOC-HIGH > SY-DATUM.
MESSAGE E011 WITH TEXT-011.
ENDIF.
ENDLOOP.
*VAL....4
if P_DOWN = 'X' AND P_PATH is initial.
MESSAGE E011 WITH TEXT-011.
endif.

if P_DW_RP = 'X' AND P_path is initial.
MESSAGE E011 WITH TEXT-011.
endif.

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