Becoz of the if user click on the basic list on the record
the detail information is stored into the secondary list.
This is done by the interactive report. But we don't use the
classical report in ALV's

Yes, we can generate both classical and Interactive reportS 
in ALV..
  
For classical report in ALV..
Type-pools : slis.

DATA :  it_Fcat type slis_T_fieldcat_Alv
        wa_fcat type slis_fieldcat_Alv.

Data  : itab type standard table of (SOme Structure)
         wa  like line ot itab.

Start-of-selection.
  Select.....

  after readig data from database....

we use FM REUSE_ALV_FIELDCATALOG_MERGE

After that We display the Output

We use FM :  REUSE_ALV_GRID_DISPLAY ( for Grid Format)
                   OR
             REUSE_ALV_LIST_DISPLAY(for list format)
*****
*&----INTERACITVE ALV*******
We take two Internal tables ...
Data : itab type standard table of ty_marc (Type structure)
       itab1 type standard table of ty_mara(TYPE structure)

data  : it_fcat type slis_t_fieldcat_alv,
        t_Event type slis_t_event,
        t_listheader type slis_t_listheader.

we use FM : REUSE_ALV_GET_EVENT
This is function Module is used to catch the EVENTs like 
TOP-OF-PAGE and END-OF-PAGE, USER_COMMAND....etc

For interactive Report:
 we will give form like

Form User_Command Using ucomm like Sy-ucomm
                   selfld type SLIS_SELFIELD,
 
*& we'll call this Subroutine in the FM GRID DISPLAY..

  case ucomm.
   
    when '&IC1'. " this is FunctionCode which catchs when 
user do some actions.
     READ TABLE Itab INTO WA_tab INDEX RS_SELFIELD-TABINDEX.
      perform buildcatlog.
      perform DataRetrieval.l
      Perform Listdisplay.
      Perfrom Dispaly.

  endcase.

THIS IS HOW WE DO INTERACTIVE ALV...
 I THINK THIS WIIL U IN DOING CLASSICAL AND INTERACTIVE 
ALV..