https://qooah.com/2011/11/28/google%e7%82%baandroid%e8%a8%ad%e8%a8%88%e5%8d%87%e7%b4%9a%e6%8e%a8%e5%87%ba%e6%96%b0%e5%b7%a5%e5%85%b7/