procedure OnDxListeCompare(Sender: TObject; Node1, Node2: TdxTreeListNode;
   var Compare: Integer);
var
   i           : integer;
   Col         : TdxTreeListColumn;

   iColID      : integer;
   Var1        : variant;
   Var2        : variant;
   IsVar1NULL  : boolean;
   IsVar2NULL  : boolean;

   Grid        : TCustomdxTreeListControl;
begin
   Compare:=0;

   if Sender is TCustomdxTreeList then
   begin
      Grid:=TCustomdxTreeListControl(Sender);

      for i:=0 to Grid.SortedColumnCount-1 do
      begin
         Col:=Grid.SortedColumns[i];
         iColID:=Col.Index;

         Var1:=Node1.Values[iColID];
         Var2:=Node2.Values[iColID];

         IsVar1NULL:=VarIsEmpty(Var1) or VarIsNull(Var1);
         IsVar2NULL:=VarIsEmpty(Var2) or VarIsNull(Var2);

         if IsVar1NULL or IsVar2NULL then
         begin
            if IsVar1NULL and IsVar2NULL then Compare:=0
            else
            if IsVar1NULL then Compare:=-1
            else
               Compare:=+1;
         end
         else
         begin
            if Var1<Var2 then Compare:=-1
            else
            if Var1>Var2 then Compare:=+1
            else
               Compare:=0;
         end;

         if Col.Sorted=csDown then Compare:=-Compare;

         if Compare<>0 then break;
      end; //for i
   end; //if Sender is TCustomdxTreeList
end;