Build field catalog for dynamic data objects

Question

Hi
Could you please tell me how to build a field catalog (ooops alv)  for an internal table which is a dynamic data object.
  TYPES: BEGIN OF t_addsubty,
         subty TYPE subty,
         pernr TYPE persno,
         END OF t_addsubty.
  TYPES: ty_addsubty type t_addsubty occurs 1.
i have data object using these
        CREATE DATA dref3 TYPE (g_type1).
        ASSIGN dref3->* TO <fs_dp>.
where g_type1 refers a data type which i defined in the program. g_type1 = ty_addsubty. 
now <fs_dp> refers to an internal table.
now i want to build a field catalog for this internal table.
In my program <fs_dp> structure is not always the same. i.e now it is ty_addsubty but for some other conditions the structure is different.
please help me out.
regards
badri

Answer 1

Here some piece of code, which shows how it works:
<SNIP>
type-pools:
     abap.
DATA:
  lr_tabledescr          TYPE REF TO cl_abap_tabledescr,
  lr_structdescr     TYPE REF TO cl_abap_structdescr.
field-symbols:
  <lw_component>     type abap_compdescr_tab.
TYPES:
     BEGIN OF t_addsubty,
          subty TYPE subty,
          pernr TYPE persno,
     END OF t_addsubty.
TYPES:
     ty_addsubty type t_addsubty occurs 1.
CREATE DATA dref3 TYPE (g_type1).
ASSIGN dref3->* TO <fs_dp>.
lr_tabledescr ?= cl_abap_tabledescr=>describe_by_data( <fs_dp> ).
assert condition lr_tabledescr is bound.
lr_structdescr ?= lr_tabledescr->get_table_line_type( ).
loop at lr_structdescr->components assigning <lw_component>.
*     do whatever you want with the information about
*     the components of the structure
endloop.
</SNIP>
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