BBC BASIC Programmers' Reference

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=====Creating child controls in a loop=====

//by Richard Russell, March 2013//\\ \\  In Liberty BASIC 4.04 you can use the **MAPHANDLE** statement to, for example, reuse the same code to open multiple windows. The LB4 documentation illustrates how to open three windows using this technique:\\ 
<code lb>
    winName$ = "first second third"
    for x = 1 to 3
      call createWindow word$(winName$, x)
    next x
    wait

  sub createWindow title$
    texteditor #1.te, 10, 10, 200, 200
    open "text "+title$ for window as #1
    #1.te "this is the "+title$+" window"
    #1 "trapclose aboutToClose"
    handle$ = "#"+title$
    maphandle #1, handle$
  end sub

  sub aboutToClose handle$
    confirm "Close "+handle$+"?"; answer
    if answer = 1 then close #handle$
  end sub
</code>
It would be extremely useful to be able to use MAPHANDLE in a similar fashion to create multiple **child controls**, but for some reason LB4 will not let you do so. Fortunately this is one of the many limitations that is removed in **LB Booster**.\\ \\  The code below is adapted from the Alphabet Buttons example on the [[http://basic.wikispaces.com/Alphabet+Buttons|Liberty BASIC Community Wiki]] but instead of using a separate BUTTON statement for each button, all 26 are created in a loop:\\ 
<code lb>
      Stylebits #win, 0,_WS_MAXIMIZEBOX,0,0
      WindowWidth = 230
      WindowHeight = 80
      UpperLeftX=int((DisplayWidth-WindowWidth)/2)
      UpperLeftY=int((DisplayHeight-WindowHeight)/2)

      for i = 1 to 26
        x = 15 * i : y = 5
        if x > 195 then x = x - 195 : y = y + 15
        Button #win.tmp, CHR$(64+i), sel, UL, x, y,  15,  15
        maphandle #win.tmp, "#win." + chr$(64+i)
      next

      Open "Alphabet Buttons" For Window As #win
      Print #win, "Trapclose quit"
      wait

  sub sel handle$
      print "Selected "; handle$
  end sub

  sub quit handle$
      close #handle$
      end
  end sub
</code>
If you click a button and watch the mainwin you can see that each button has a separate handle, exactly as was the case in the original program.