Making a field dynamically mandatory-Issue in get_p

Hi friends,

I am working on a very simple requirement.

I have a custom field A (drop down with 4 values).

1

2

3

4

If I select the value 1 in drop down, the field B(which is again a custom drop down field) should be mandatory. If I select any other values like 2,3 or 4, Field B shouldn't be mandatory. I followed the typical approach of making mandatory via get_p with following coding.

WHEN if_bsp_wd_model_setter_getter~fp_input_mandatory.

      IF lv_field_active = '1'.
           rv_value = abap_true.
         ELSE.
           rv_value = abap_false.
       ENDIF.

It's working fine to make it mandatory. However, If I choose some other value again, it's not setting the field to non mandatory in the first step. If I allow one more server round trip by clicking on some other fields or choose any other value in the drop down, it's non mandatory.

Eg.

I choose value 1 ->Field B mandatory.

I choose value 2 -> Field B mandatory again(not expected)

I click on some other fields which have server round trip or I choose value 3 ->Field not mandatory.

What is the reason it's not working in the first step?.

I could achieve the functionality via iterator class though, need to know the reason here.

Thanks,

Faisal