Hi, Dears.
I want to inform that it is possible to fix the width of columns in ALV.
It is necessary to create new class <lcl_my_grid > inheriting from cl_gui_alv_grid.
In this new class you should create method set_no_resize.
METHOD set_no_resize.
CALL METHOD me->set_resize_cols
EXPORTING
enable = 0
EXCEPTIONS
error = 1
OTHERS = 2.
ENDMETHOD.
Call this method to prevent the user to change the column size.
You can find more information here