Cl_GUI_ALV_GRID Fields are not getting editable

HI,

In a Cl_GUI_ALV_GRID , ALV Grid Program i  want to enable the edit option (Functionality) of any of the displaying fields based on the cutom tool button selection. But it's not happend,

kinldy check the below code and suggest what i need to be add extra.

         LOOP AT CIT_FCT INTO CFL_FCT WHERE FIELDNAME EQ 'FIEL_NAME'.
               CFL_FCT-EDIT = 'X'.
         MODIFY CIT_FCT FROM CFL_FCT INDEX SY-TABIX.
        ENDLOOP.
        CALL METHOD CL_ALV->REFRESH_TABLE_DISPLAY.
        CALL METHOD CL_GUI_CFW=>FLUSH.

Thanks & Regard

Praveer.