Android在隐藏底部虚拟按键的时候Google官方答案
https://developer.android.com/training/system-ui/navigation.html#behind
代码示例：
View decorView = getWindow().getDecorView();
int uiOptions = View.SYSTEM_UI_FLAG_HIDE_NAVIGATION
| View.SYSTEM_UI_FLAG_FULLSCREEN;
decorView.setSystemUiVisibility(uiOptions);
但是这样会出现一个问题，就是在界面上如果有按钮那么点击这个按钮要点击2次才能触发点击事件！
最终解决应该是
//隐藏虚拟按键，并且全屏
if (Build.VERSION.SDK_INT > 11 && Build.VERSION.SDK_INT < 19) { // lower api
View v = this.getWindow().getDecorView();
v.setSystemUiVisibility(View.GONE);
} else if (Build.VERSION.SDK_INT >= 19) {
//for new api versions.
View decorView = getWindow().getDecorView();
int uiOptions = View.SYSTEM_UI_FLAG_HIDE_NAVIGATION
| View.SYSTEM_UI_FLAG_IMMERSIVE_STICKY | View.SYSTEM_UI_FLAG_FULLSCREEN;
decorView.setSystemUiVisibility(uiOptions);
}
