delphi – 我可以以编程方式设置ComboBox下拉列表的位置吗？

TForm1 = class(TForm)
  ComboBox1: TComboBox;
  procedure FormCreate(Sender: TObject);
  procedure FormDestroy(Sender: TObject);
private
  FComboBoxListDropDown: Boolean;
  FComboBoxListWnd: HWND;
  FOldComboBoxListWndProc,FNewComboBoxListWndProc: Pointer;
  procedure ComboBoxListWndProc(var Message: TMessage);
end;

....

procedure TForm1.FormCreate(Sender: TObject);
var
  Info: TComboBoxInfo;
begin
  ZeroMemory(@Info,SizeOf(Info));
  Info.cbSize := SizeOf(Info);
  GetComboBoxInfo(ComboBox1.Handle,Info);
  FComboBoxListWnd := Info.hwndList;
  FNewComboBoxListWndProc := MakeObjectInstance(ComboBoxListWndProc);
  FOldComboBoxListWndProc := Pointer(GetWindowLong(FComboBoxListWnd,GWL_WNDPROC));
  SetWindowLong(FComboBoxListWnd,GWL_WNDPROC,Integer(FNewComboBoxListWndProc));
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  SetWindowLong(FComboBoxListWnd,Integer(FOldComboBoxListWndProc));
  FreeObjectInstance(FNewComboBoxListWndProc);
end;

procedure TForm1.ComboBoxListWndProc(var Message: TMessage);
var
  R: TRect;
  DY: Integer;
begin
  if (Message.Msg = WM_MOVE) and not FComboBoxListDropDown then
  begin
    FComboBoxListDropDown := True;
    try
      GetWindowRect(FComboBoxListWnd,R);
      DY := (R.Bottom - R.Top) + ComboBox1.Height + 1;
      // set new Y position for drop-down list: always above ComboBox1
      SetWindowPos(FComboBoxListWnd,R.Left,R.Top - DY,SWP_NOOWNERZORDER or SWP_NOZORDER or SWP_NOSIZE  or SWP_NOSENDCHANGING);
    finally
      FComboBoxListDropDown := False;
    end;
  end;
  Message.Result := CallWindowProc(FOldComboBoxListWndProc,FComboBoxListWnd,Message.Msg,Message.WParam,Message.LParam);
end;

笔记：

>我完全同意David和其他人的意见,这对于改变TComboBox的这种特定默认行为是一个坏主意. OP尚未回应为什么他想要这样的行为.>上面的代码是用D5 / XP测试的.