好吧终于解开了它的棒棒糖。但我没有在设备测试低于棒棒糖。

Ok finally solved it in lollipop. But i haven't tested in devices lower than lollipop.

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
        Window window = getWindow();
        window.addFlags(WindowManager.LayoutParams.FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS);
        window.setStatusBarColor(Color.TRANSPARENT);
        window.setNavigationBarColor(Color.TRANSPARENT);
    }