Using Selection screen in Initial screen of FPM and how to pass to process_event method

I want to write an OIF FPM WDA with initial screen as selection screen using WDR_SELECT_OPTIONS but I do not know how to correctly retrieve and pass the selected value entered in the initial screen in order to process.

In my application, I have a view V_INITIAL with usage component WDR_SELECT_OPTIONS) and V_MAIN with 2 tabs for data retrieved from selection screen in V_INITIAL. I am using OIF component.

On initial screen, I have selection input fields sales area, document type and  soldto customer range. I was able to set the default value on the initial screen in the WDDOINIT of the V_INITIAL view.  But after user enter value, in which method should I code so that I can get the value user entered ?

I was trying to put code in method WDDOBEFOREACTION to get the value and store in global attributes declared from component controller (See below code) but I have issue when user change default value and click button continue in initial screen without hit enter key, the value I get is still as the default value.  If after user change value and hit enter key

Is it possible to use inital screen in FPM with select options?  I search but could not find a similar scenario.

Here is my code:

method wddobeforeaction.   "In V_INITIAL view

field-symbols:

   <fval> type any,

   <ls_field> type LINE OF if_wd_select_options=>tt_selection_screen_item

data: lr_helper TYPE REF TO if_wd_select_options.

data lt_fields type if_wd_select_options=>tt_selection_screen_item

lr_helper->get_selection_screen_items( IMPORTING
     et_selection_screen_items = lt_fields ).

  Loop at lt_fields ASSIGNING <ls_field>.
  case <ls_field>-m_id.

        when 'SPART'.

        ASSIGN <ls_field>-m_value->*  to <fval>.
        wd_comp_controller->gv_sel_spart = <fval>.

       when 'KUNNR'.    

       ASSIGN <ls_field>-mt_range_table->* to <lt_range_table>.
        wd_comp_controller->gt_sel_soldto = <lt_range_table>.

      when others.

  endcase.

..  Later on, in process_event mehod of component controller, I check if the event is leaving initial screen, I will extract data from the input selection fields user entered.

Can someone advise is this a correct approach or should I just use a regular view for user input selection and create action to capture input value?

Please advise.

Thanks