https://qooah.com/2011/11/17/%e5%85%a8%e7%90%83android%e6%83%a1%e6%84%8f%e8%bb%9f%e4%bb%b6%e6%b0%be%e6%bf%ab%e6%88%90%e7%81%bd%e9%81%8e%e5%8e%bb4%e6%9c%88%e5%a2%9e%e9%95%b75%e5%80%8d-2/