Object oriented ALV..get_selected_rows not working...URGENT !!!

Hi Experts,

I am using Object oreinted ALV and used set_table_for_first_display to display values and in layout i made SEL_MODE as A.

After displaying the list I want to get the rows that are selected and for this I used the method

CALL METHOD gr_alvgrid->get_selected_rows..

But I am not getting values from either et_index_rows or et_row_no...both of them are initial.

even if I change sel_mode to D , i am not getting the values of selected rows...

Another info......I populated the fieldcatalog manually..

please tell me how I can get the multiple selected rows.

Thanks in Advance,

KK.