DecorView是窗口最顶层的视图,其具体意思及用法参考
http://www.cnblogs.com/beenupper/archive/2012/07/13/2589749.html
获得当前活动的DecorView通过下面一行代码
View decorView=getWindow().getDecorView();
setSystemUiVisibility方法和getSystemUiVisibility方法的意思及用法参考,
http://www.cnblogs.com/8dull/p/5383135.html