I have been looking in the forums for ways of making a CL_GUI_ALV_GRID grid editable for the user in a way that whatever value they put in the cells gets registered in the iternal table being displayed on that ALV, but most of the content I found were solutions using the FUNCTION ‘REUSE_ALV_GRID_DISPLAY_LVC’, but in my case I couldn’t use this function module because the program I was editing was already buit with CL_GUI_ALV_GRID, so I had to find out by myself (and with a little help from ChatGPT).

This is how it looks like

Here is the code I wrote. Don’t forget to add a button with code ‘SWITCH’ for calling the f_switch_edit_mode  subroutine.

*&---------------------------------------------------------------------*
*& Report  Z_EDITABLE_ALV_GRID -  Made with help of ChatGPT
*&---------------------------------------------------------------------*

REPORT z_editable_alv_grid.

* Types----------------------------------------------------------------*
TYPES BEGIN OF y_orders_c.
TYPES mu       TYPE mseg-erfme.
TYPES quant     TYPE mseg-lsmng.
TYPES quant2  TYPE mseg-lsmng. "make editable
TYPES mu2       TYPE mseg-lsmeh.
TYPES celltab   TYPE lvc_t_styl.
TYPES END OF y_orders_c.

* Declare local variables----------------------------------------------*
DATA: lo_grid     TYPE REF TO cl_gui_alv_grid,
      lt_fieldcat TYPE lvc_t_fcat,
      lt_data     TYPE TABLE OF y_orders_c.

DATA: gs_alv_layout TYPE lvc_s_layo .

DATA: e_cell_type TYPE lvc_s_styl.

DATA e_orders_c TYPE y_orders_c.

START-OF-SELECTION.

  CALL SCREEN 100.

MODULE show_orders OUTPUT.

  IF NOT lo_grid IS BOUND.

* Populate field catalog-----------------------------------------------*
    PERFORM f_fieldcat USING  lt_data[]
                      CHANGING  lt_fieldcat.
    LOOP AT lt_fieldcat ASSIGNING FIELD-SYMBOL(<fs_fieldcat>).

      CASE <fs_fieldcat>-fieldname.
        WHEN 'MU'.
          <fs_fieldcat>-coltext = 'MU'.
        WHEN 'QUANT'.
          <fs_fieldcat>-coltext = 'Original qtd.'.
        WHEN 'QUANT2'.
          <fs_fieldcat>-edit = 'X'. "Set field to editable
          <fs_fieldcat>-coltext = 'New qtd.'.
        WHEN 'MU2'.
          <fs_fieldcat>-coltext = 'New MU'.
      ENDCASE.
    ENDLOOP.

* Layout options-------------------------------------------------------*
    CLEAR gs_alv_layout.
    MOVE abap_true TO: gs_alv_layout-cwidth_opt,
                       gs_alv_layout-zebra,
                       gs_alv_layout-col_opt.
    gs_alv_layout-stylefname = 'CELLTAB'.


* Populate data--------------------------------------------------------*
    e_orders_c-mu = 'KG'.
    e_orders_c-quant = '2000'.
    e_orders_c-quant2 = '2'.
    e_orders_c-mu2 = 'TO'.
    APPEND e_orders_c TO lt_data.

    CLEAR e_orders_c-mu.
    e_orders_c-mu = 'KG'.
    e_orders_c-quant = '7000'.
    e_orders_c-quant2 = '7'.
    e_orders_c-mu2 = 'TO'.
    APPEND e_orders_c TO lt_data.

    CLEAR e_orders_c-mu.
    e_orders_c-mu = 'KG'.
    e_orders_c-quant = '15000'.
    e_orders_c-quant2 = '15'.
    e_orders_c-mu2 = 'TO'.
    APPEND e_orders_c TO lt_data.

    CLEAR e_orders_c-mu.
    e_orders_c-mu = 'KG'.
    e_orders_c-quant = '2500'.
    e_orders_c-quant2 = '2.5'.
    e_orders_c-mu2 = 'TO'.
    APPEND e_orders_c TO lt_data.

    CLEAR e_orders_c-mu.
    e_orders_c-mu = 'KG'.
    e_orders_c-quant = '1000'.
    e_orders_c-quant2 = '1'.
    e_orders_c-mu2 = 'TO'.
    APPEND e_orders_c TO lt_data.


* Create ALV grid and display------------------------------------------*
    CREATE OBJECT lo_grid
      EXPORTING
        i_parent = cl_gui_container=>screen0.

    CALL METHOD lo_grid->set_table_for_first_display
      EXPORTING
        i_structure_name = 'LT_DATA'
        is_layout        = gs_alv_layout
      CHANGING
        it_outtab        = lt_data
        it_fieldcatalog  = lt_fieldcat.

* Register event for cell editing--------------------------------------*
    CALL METHOD lo_grid->register_edit_event
      EXPORTING
        i_event_id = cl_gui_alv_grid=>mc_evt_enter
      EXCEPTIONS
        error      = 1
        OTHERS     = 2.
    IF sy-subrc <> 0.
      MESSAGE ID sy-msgid TYPE sy-msgty NUMBER sy-msgno
        WITH sy-msgv1 sy-msgv2 sy-msgv3 sy-msgv4.
    ENDIF.

  ELSE.
    PERFORM f_update_grid USING lo_grid.
  ENDIF.

ENDMODULE.                 " SHOW_ORDERS  OUTPUT


*&---------------------------------------------------------------------*
*&      Module  STATUS_0100  OUTPUT
*&---------------------------------------------------------------------*
*       text
*----------------------------------------------------------------------*
MODULE status_0100 OUTPUT.
  SET PF-STATUS 'STATS100'.
*  SET TITLEBAR 'your title here'.
ENDMODULE. "status_0100


*&---------------------------------------------------------------------*
*&      Module  USER_COMMAND_0100  INPUT
*&---------------------------------------------------------------------*
*       text
*----------------------------------------------------------------------*
MODULE user_command_0100 INPUT.
  CASE sy-ucomm.
    WHEN 'BACK' OR 'EXIT' OR 'CANCEL'.
      LEAVE TO SCREEN '0'.
    WHEN 'SWITCH'.
      PERFORM f_switch_edit_mode.
    WHEN OTHERS.
*     do nothing
  ENDCASE.
ENDMODULE. "user_command_0100


*&---------------------------------------------------------------------*
*&      Form  F_FIELDCAT
*&---------------------------------------------------------------------*
FORM f_fieldcat USING     pt_table     TYPE ANY TABLE
                  CHANGING  pt_fieldcat  TYPE lvc_t_fcat.

  DATA:
    lr_tabdescr TYPE REF TO cl_abap_structdescr,
    lr_data     TYPE REF TO data,
    lt_dfies    TYPE ddfields,
    ls_dfies    TYPE dfies,
    ls_fieldcat TYPE lvc_s_fcat.
  
  CLEAR pt_fieldcat.

  CREATE DATA lr_data LIKE LINE OF pt_table.
  lr_tabdescr ?= cl_abap_structdescr=>describe_by_data_ref( lr_data ).
  lt_dfies = cl_salv_data_descr=>read_structdescr( lr_tabdescr ).

  LOOP AT lt_dfies INTO ls_dfies.
    CLEAR ls_fieldcat.
    MOVE-CORRESPONDING ls_dfies TO ls_fieldcat.
    APPEND ls_fieldcat TO pt_fieldcat.
  ENDLOOP.
ENDFORM. "f_fieldcat


*&---------------------------------------------------------------------*
*&      Form  SWITCH_EDIT_MODE
*&---------------------------------------------------------------------*
FORM f_switch_edit_mode.

  IF lo_grid->is_ready_for_input( ) EQ 0.
* set edit enabled cells ready for input
    CALL METHOD lo_grid->set_ready_for_input
      EXPORTING
        i_ready_for_input = 1.

  ELSE.
* lock edit enabled cells against input
    CALL METHOD lo_grid->set_ready_for_input
      EXPORTING
        i_ready_for_input = 0.
  ENDIF.
ENDFORM. " f_switch_edit_mode


*&---------------------------------------------------------------------*
*&      Form  F_UPDATE_GRID
*&---------------------------------------------------------------------*
FORM f_update_grid USING p_grid TYPE REF TO cl_gui_alv_grid.

  DATA vl_stable TYPE lvc_s_stbl.

  CHECK p_grid IS BOUND.

  CLEAR vl_stable.
  MOVE abap_true TO:
    vl_stable-col,
    vl_stable-row.

  CALL METHOD p_grid->refresh_table_display
    EXPORTING
      is_stable = vl_stable
    EXCEPTIONS
      OTHERS    = 99.

  IF sy-subrc NE 0.
    RETURN.
  ENDIF.

ENDFORM.                    "f_update_grid

Code for the screen being called:

PROCESS BEFORE OUTPUT.
  MODULE status_0100.
  MODULE show_orders.

PROCESS AFTER INPUT.
  MODULE user_command_0100.

I hope it becomes useful for someone out there 😀

Edit: forgot to add the image lol