function WndOnCheck(Sender: PControl; var Msg: TMsg; var Rslt: Integer): Boolean;
const
  NM_FIRST      = 0;
  NM_CLICK      = NM_FIRST - 2;
  NM_CUSTOMDRAW = NM_FIRST - 12; 
type
  tagNMITEMACTIVATE = packed record
    hdr: TNMHdr;
    iItem: Integer;
    iSubItem: Integer;
    uNewState: UINT;
    uOldState: UINT;
    uChanged: UINT;
    ptAction: TPoint;
    lParam: LPARAM;
    uKeyFlags: UINT;
  end;
  PNMItemActivate = ^TNMItemActivate;
  TNMItemActivate = tagNMITEMACTIVATE;
var
  NMOD: PNMItemActivate;
  fClass: ThiTreeViewTrain;
  fd: PData;
  where: dword;
  ItemStateImg, i: integer;

  procedure Enum(prn: cardinal; CheckBoxes: boolean; CheckBoxIndex: integer);
  var
    j: integer;
    FCurNode: PData;
  begin
    if prn > 0 then 
    begin
      FCurNode := PData(Sender.TVItemData[prn]);
      j := 0;
      while FCurNode <> nil do      
      begin  
        if CheckBoxes and (j = CheckBoxIndex) and (ItemStateImg <> ToInteger(FCurNode^) + 1) then
        begin
          if _IsInteger(FCurNode^) then
          FCurNode.idata := ItemStateImg - 1
          else if _IsStr(fd^) then
            FCurNode.sdata := Int2Str(ItemStateImg - 1)
          else
          begin
            FCurNode.idata := ItemStateImg - 1;
            FCurNode.sdata := Int2Str(ItemStateImg - 1);
            FCurNode.rdata := ItemStateImg - 1;            
          end;
          Sender.TVItemStateImg[prn] := ItemStateImg;
          break;
        end;  
        inc(j);
        FCurNode := FCurNode.ldata;
      end;
      if Sender.TVItemChild[prn] > 0 then Enum(Sender.TVItemChild[prn], CheckBoxes, CheckBoxIndex);
      Enum(Sender.TVItemNext[prn], CheckBoxes, CheckBoxIndex);
    end;
  end;

begin
  Result := false;
  fClass := ThiTreeViewTrain(Sender.Tag);
  with fClass do
  begin
    if Msg.message = WM_NOTIFY then
    begin
      NMOD := Pointer( Msg.lParam );
      if (NMOD.hdr.code = NM_CLICK) then 
        PostMessage(Sender.Handle, WM_STATECHANGED, 0, Sender.TVItemAtPos(Ms.X, Ms.Y, where));
	end;    
    if (Msg.message = WM_STATECHANGED) and (Msg.LParam <> 0) then
    begin
      ItemStateImg := Sender.TVItemStateImg[Msg.LParam];

      fd := Sender.TVItemData[Msg.LParam];
      i := 0;
      while fd <> nil do      
      begin  
        if _prop_CheckBoxes and (i = _prop_CheckBoxIndex) and (ItemStateImg <> ToInteger(fd^) + 1) then
        begin
          if _IsInteger(fd^) then
            fd.idata := ItemStateImg - 1
          else if _IsStr(fd^) then
            fd.sdata := Int2Str(ItemStateImg - 1)
          else
          begin
            fd.idata := ItemStateImg - 1;
            fd.sdata := Int2Str(ItemStateImg - 1);
            fd.rdata := ItemStateImg - 1;            
          end;
          if _prop_SetCheckOnChild then
            Enum(Sender.TVItemChild[Msg.LParam], _prop_CheckBoxes, _prop_CheckBoxIndex);
          break;
        end;  
        inc(i);
        fd := fd.ldata;
      end;
    end;  
  end;  
end;