Hide a obligatory parameter when changing radio buttons

Question

I have some radiobuttons and when I change between them some blocks appear/disappear.

However, if I set parameters as obligatory or required they do not hide unless I fill them. I want to make parameters required but I need to hide them when I change the radiobutton option.

Solution

If you use PARAMETERS ... OBLIGATORY, this is an unconditional statement - this parameter is required regardless of the other settings. If you need a conditional check, you have to code it for yourself:

PARAMETERS p_chkbuk AS CHECKBOX.
PARAMETERS p_bukrs  TYPE bukrs.

AT SELECTION-SCREEN ON p_bukrs. 
  IF p_chkbuk = abap_true AND p_bukrs IS INITIAL. 
    MESSAGE 'You need to enter something.' TYPE 'I' DISPLAY LIKE 'E'.
  ENDIF.