How to Disable field in Selection-screen

Question

Hi All,
I want to disable Screen field in my seelction screen. Below is my Code, but it is not working.
I want to perform.
If RB1 = X
Then Parameter P_VBELN should get disabled. Please suggest, find below my code.
*....Selection Screen
selection-screen begin of block b1 with frame title text-001.
parameters: p_vbeln like vbak-vbeln.
selection-screen end of block b1.
selection-screen begin of block b2 with frame title text-002.
parameter: rb1 radiobutton group radi default 'X',
           rb2 radiobutton group radi.
selection-screen end of block b2.
*....At Selection Screen
AT Selection-screen.
  if p_vbeln = ''.
    MESSAGE ID 'ZID' TYPE 'E' NUMBER '000'.
  endif.
*....At selection screen output
AT Selection-screen output.
  if rb1 = 'X'.
    Loop at screen.
      if screen = 'P_VBELN'.
        screen-input = '0'.
      endif.
      modify screen.
    endloop.
  endif.
*....Start of selection
Start-of-Selection.
  select *
  from vbak into table itab1
   where vbeln = p_vbeln.
  if itab1 is initial.
    select *
    from vbap into table itab2
    for all entries in itab1
    where vbeln = itab1-vbeln.
  endif.

Answer 1

Hi Kamaljeet ,
In the code below..see the lines in BOLD..explanation is given as to why they are required
Code----
selection-screen begin of block b1 with frame title text-001.
parameters: p_vbeln like vbak-vbeln.
selection-screen end of block b1.
selection-screen begin of block b2 with frame title text-002.
parameter: rb1 radiobutton group radi default 'X' user-command ucomm,
rb2 radiobutton group radi.
selection-screen end of block b2.
AT Selection-screen output.
if rb1 = 'X'.
Loop at screen.
if screen-name = 'P_VBELN'.
screen-input = '0'.
endif.
modify screen.
endloop.
else.
Loop at screen.
if screen-name = 'P_VBELN'.
screen-input = '1'.
endif.
modify screen.
endloop.
endif.
Explanation----
If the user command is not given,the system will not trigger on the click of radio button..
Once triggered it comes to "At selection screen output"..where we must also mention the case when
radio button 2 is selected RB2 ..the p_vbeln must be input and when RB1 is selected the field
p_vbeln must be display only..Paste the code and see how it works
Then use the logic as desired...
Hope it helps
Regards
Byju