How to deal with table control / step loop in BDC?

Steploop and table contol is inevitable in certain transactions. When we run BDC for such transactions, we will face the situation: how many visible lines of steploop/tablecontrol are on the screen? Although we can always find certain method to deal with it, such as function code 'NP', 'POPO', considering some extreme situation: there is only one line visible one the screen,
our BDC program should display an error message. (See transaction 'ME21', we you resize your screen to let only one row visible, you can not enter mutiple lines on this screen even you use 'NP')
Now, I find a method with which we can determine the number of visible lines on Transaction Screen from our Calling BDC program. Maybe it is useless to you, but I think it will give your some idea.

Demo ABAP code has two purposes:
1. how to determine number of visible lines and how to calculte page number; (the 'calpage' routine has been modify to meet general purpose usage)
2. using field symbol in BDC program, please pay special attention to the difference in Static

ASSIGN and Dynamic ASSIGN.

Now I begin to describe the step to implement my method:
(I use transaction 'ME21', screen 121 for sample, the method using is Call Transation Using..)
Step1: go to screen painter to display the screen 121, then we can count the fixed line on this screen, there is 7 lines above the steploop and 2 lines below the steploop, so there are total 9 fixed lines on this screen. This means except these 9 lines, all the other line is for step loop.

Then have a look at steploop itselp, one entry of it will occupy two lines.
(Be careful, for table control, the head and the bottom scroll bar will possess another two fixed lines, and there is a maximum number for table line)

Now we have : FixedLine = 9
              LoopLine  = 2(for table control, LoopLine is always equal to 1)

Step2: go to transaction itself(ME21) to see how it roll page, in ME21, the first line of new page is always occupied by the last line of last page, so it begin with index '02', but in some other case, fisrt line is empty and ready for input.

Now we have: FirstLine = 0
          or FirstLine = 1 ( in our case, FirstLine is 1 because the first line of new page is fulfilled)

Step3: write a subroutine calcalculating number of pages
(here, the name of actual parameter is the same as formal parameter)

global data:    FixedLine type i, " number of fixed line on a certain screen
                LoopLine  type i, " the number of lines occupied by one steploop item
                FirstLine type i, " possbile value 0 or 1, 0 stand for the first line of new
                                                         " scrolling screen is empty, otherwise is 1
                Dataline  type i, " number of items you will use in BDC, using DESCRIBE to get
                pageno    type i, " you need to scroll screen how many times.
                line      type i, " number of lines appears on the screen.
                index(2)  type N, " the screen index for certain item
                begin     type i, " from parameter of loop
                end       type i. " to parameter of loop

*in code sample, the DataTable-linindex stands for the table index number of this line
 

form calpage using FixedLine type i (see step 1)
                   LoopLine  type i (see step 1)
                   FirstLine type i (see step 2)
                   DataLine  type i ( this is the item number you will enter in transaction)
          changing pageno    type i (return the number of page, depends on run-time visible  line in table control/ Step Loop)
          changing line      type i.(visible lines one the screen)
data: midd type i,
      vline type i, "visible lines
if DataLine eq 0.
   Message eXXX.
endif.

vline = ( sy-srows - FixedLine ) div LoopLine.
*for table control, you should compare vline with maximum line of
*table control, then take the small one that is min(vline, maximum)
*here only illustrate step loop

if FirstLine eq 0.
        pageno = DataLine div vline.

        if pageno eq 0.
           pageno = pageno + 1.
        endif.
elseif FirstLine eq 1.
        pageno = ( DataLine - 1 ) div ( vline - 1 ) + 1.
        midd = ( DataLine - 1 ) mod ( vline - 1).
        if midd = 0 and DataLine gt 1.
                pageno = pageno - 1.
        endif.
endif.

line = vline.

endform.

Step4 write a subroutine to calculate the line index for each item.

form calindex using Line type i (visible lines on the screen)
                    FirstLine type i(see step 2)
                    LineIndex type i(item index)
          changing  Index type n.    (index on the screen)

  if  FirstLine = 0.
        index = LineIndex mod Line.
        if index = '00'.
                index = Line.
        endif.
  elseif FirstLine = 1.
        index = LineIndex mod ( Line - 1 ).
        if ( index between 1 and 0 ) and LineIndex gt 1.
                index = index + Line - 1.
        endif.
        if Line = 2.
                index = index + Line - 1.
        endif.
 endif.

endform.

Step5 write a subroutine to calculate the loop range.

form calrange using Line type i ( visible lines on the screen)
                    DataLine type i
                    FirstLine type i
                    loopindex like sy-index
        changing    begin type i
                    end type i.

If FirstLine = 0.
   if loopindex = 1.
        begin = 1.
        if DataLine <= Line.
                end = DataLine.
        else.
                end = Line.
        endif.
   elseif loopindex gt 1.
        begin = Line * ( loopindex - 1 ) + 1.
        end   = Line * loopindex.
        if end gt DataLine.
           end = DataLine.
        endif.
   endif.

elseif FirstLine = 1.

  if loopindex = 1.
        begin = 1.
        if DataLine <= Line.
                end = DataLine.
        else.
                end = Line.
        endif.
  elseif loop index gt 1.
        begin = ( Line - 1 ) * ( loopindex - 1 ) + 2.
        end =   ( Line - 1 ) * ( loopindex - 1 ) + Line.
        if end gt DataLine.
                end = DataLine.
        endif.
  endif.

endif.

endform.
 

Step6 using field sysbol in your BDC, for example: in ME21, but you should calculate each item will correponding to which index in steploop/Table Control

form creat_bdc.

field-symbols: <material>, <quan>, <indicator>.

data: name1(14) value 'EKPO-EMATN(XX)',
      name2(14) value 'EKPO-MENGE(XX)',
      name3(15) value 'RM06E-SELKZ(XX)'.
assign:         name1 to <material>,
                name2 to <quan>,
                name3 to <indicator>.
              .
do pageno times.

if sy-index gt 1

*insert scroll page ok_code"

endif.
              .
              .
        perform calrange using Line DataLine FirstLine sy-index
                         changing begin end.
              .
              .
loop at DataTable from begin to end.
        perform calindex using Line FirstLine DataTable-LineIndex changing Index.
        name1+11(2) = Index.
        name2+11(2) = Index.
        name3+12(2) = Index.
              .
              .
        perform bdcfield using <material> DataTable-matnr.
        perform bdcfield using <quan>     DataTable-menge.
        perform bdcfield using <indicator> DataTable-indicator.
              .
              .
              .

endloop.

enddo.

I only focus on the most difficult part, otherwise we will lost in the sea of code.
 
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