Hi,
You should give in get_p method Server event - dummy event.
in GET_V method of second filed get the first dropdown value and accordingly fill your second dropdown values.
CASE iv_property.
WHEN if_bsp_wd_model_setter_getter~fp_fieldtype.
rv_value = cl_bsp_dlc_view_descriptor=>field_type_picklist.
WHEN if_bsp_wd_model_setter_getter~fp_onclick.
rv_value = event name
ENDCASE.
Regards,
Deepika.