hi Sarala,
As per my experience, Yes. You have to do the coding in get_v. A sample code below for the same kind of issue I faced.
TRY.
* create the F4 value help using the Search Help and the parameter input and output mapping tables
CREATE OBJECT rv_valuehelp_descriptor TYPE cl_bsp_wd_valuehelp_f4descr
EXPORTING
iv_help_id = l_c_helpidname " data element name
iv_help_id_kind = if_bsp_wd_valuehelp_f4descr=>help_id_kind_dtel
iv_input_mapping = l_i_inmap
iv_output_mapping = l_i_outmap.
CATCH: cx_sy_create_object_error.
* Return is used instead of exception to avoid interruption in flow of standard framework,
* mentioned as Note in header.
RETURN.
ENDTRY.
Thanks,
Faisal