procedure TForm1.Edit1KeyDown(Sender: TObject; var Key: Word; Shift: TShiftState
  );
begin
  if ( key=40 ) and (listbox2.Items.Count>0) and listbox2.Visible  then begin    //defines.icn  VK_DOWN = 40;
   ListBox2.SetFocus;
   ListBox2.ItemIndex:=0;
  end;
end; 

其他参考：

带历史记忆，并模糊带出功能的Edit

链接：https://pan.baidu.com/s/1cx38hU18XnUaj4YOo7wwJw
提取码：osdr