Issue with get_selected_rows with ZCL_SALV_TABLE (done in se24)

Question

Experts,
I'm facing a problem whereby I couldn't get the selected row. My requirement is to display an ALV. User will select a row and when click on the standard SAVE button, I will run some FM. I have created a custom class in SE24 for my program and I've coded my ALV display in a method and the selection of the rows in another method.
THis is the code in my ALV creation method:
method DISPLAY_ALV.
  DATA:
    lo_container TYPE REF TO cl_gui_custom_container,
    lt_rows      TYPE salv_t_row,
    lt_column    TYPE salv_t_column,
    ls_cell      TYPE salv_s_cell.
  gt_data[] = ct_table[].
  IF lo_container IS NOT BOUND.
      IF cl_salv_table=>is_offline( ) = if_salv_c_bool_sap=>false.
        CREATE OBJECT lo_container
          EXPORTING
            container_name = 'CONTAINER'.
      ENDIF.
  TRY.
    CALL METHOD cl_salv_table=>factory
      EXPORTING
        r_container    = lo_container
        container_name = 'CONTAINER'
      IMPORTING
        r_salv_table   = go_alv
      CHANGING
        t_table        = gt_data.
    CATCH cx_salv_msg.
  ENDTRY.
  ENDIF.
  gr_selection = go_alv->get_selections( ).
  gr_selection->set_selection_mode( if_salv_c_selection_mode=>row_column ).
  go_alv->display( ).
endmethod.
What I have for the code in the row selection method is
method GET_ALV_SELECTION.
  DATA: lt_row TYPE salv_t_row.
   lt_row = gr_selection->get_selected_rows( ).
endmethod.
In my PAI, I code my user command for the SAVE button. Once pressed, I call method GET_ALV_SELECTION. I just can't seems to get the line selected. LT_ROW always return an empty table. I didn't code any event. Is that the cause?
Thanks in advance.

Answer 1

Let me rephrase my question. I have a report which display an alv which allow user to perform line selection. When user click on the SAVE button, I will run some process for the selected line. Initially, I can't even get the selected line to populate lt_row (pls refer code below). After I called method get_metadata(), then I was able to grab the row selection, but only for the first time, i.e. after I click on the SAVE button (to finish some processing) and select the row again, lt_row is empty again. Not even <<POINTA>> & <<POINTB>> is fired (pls refer code below).
I have a method (METHOD A) to display my ALV as below (coded in SE24):
DATA:
    lo_container TYPE REF TO cl_gui_custom_container,
    lt_rows      TYPE salv_t_row,
    lt_column    TYPE salv_t_column,
    ls_cell      TYPE salv_s_cell.
  gt_data[] = ct_table[].
  IF lo_container IS NOT BOUND.
      IF cl_salv_table=>is_offline( ) = if_salv_c_bool_sap=>false.
        CREATE OBJECT lo_container
          EXPORTING
            container_name = 'CONTAINER'.
      ENDIF.
  TRY.
    CALL METHOD cl_salv_table=>factory
      EXPORTING
        r_container    = lo_container
        container_name = 'CONTAINER'
      IMPORTING
        r_salv_table   = go_alv
      CHANGING
        t_table        = gt_data.
    CATCH cx_salv_msg.
  ENDTRY.
  ENDIF.
  gr_selection = go_alv->get_selections( ).
  gr_selection->set_selection_mode( if_salv_c_selection_mode=>row_column ).
  go_alv->display( ).
Then, I have a method (METHOD B ) to process get the selected lines, as below (coded in SE24):
  DATA:
    l_error TYPE char1,
    l_msg   TYPE char50,
    lt_msg  TYPE fmtx_t_text_uab,
    lt_row  TYPE salv_t_row,
    lw_row  LIKE LINE OF lt_row,
    lt_temp TYPE zp2p_t_plnord_delete,
    lw_temp TYPE zp2p_s_plnord_delete.
  lt_temp[] = gt_data[].
  "<< POINT A >>
  go_alv->get_metadata( ).    ---> initially when i don't put this, I can't even get lt_row to display the selected line.
  lt_row = gr_selection->get_selected_rows( ).
  "<< POINT A >>
  IF lt_row IS NOT INITIAL.
    "do something
  ENDIF.
"<< POINT B >>
  REFRESH: lt_row.
  gr_selection->set_selected_rows(
    EXPORTING
      value = lt_row ).
  "<< POINT B >>
  go_alv->set_data(
    CHANGING
      t_table = gt_data ).
  go_alv->display( ).
And my PAI is as below (coded in SE80):
  CASE sy-ucomm.
    WHEN lc_save.
      IF g_empty IS INITIAL.
        go_object->process_data(
          IMPORTING
            et_log        = gt_log
            e_empty_table = g_empty ).
      ELSE.
        MESSAGE S000 WITH text-050.
      ENDIF.
    WHEN OTHERS.
  ENDCASE.
So, it seems like the row selection is only fired once in my method (METHOD B). Both <<POINTA>> & <<POINTB>> is also only work once. lt_row will always be empty if this method is called another time. Seems like I'm missing some instantiation. Please do help.
Thanks in advance.