if(root_view_height < DisplayUtils.getScreenHeight(VideoPlayerActivity.this)){
                        layoutParams.bottomMargin = mainInvisibleHeight- BarUtils.getNavBarHeight();
                    }else {
                        layoutParams.bottomMargin = mainInvisibleHeight;
                    }
 

root_view_height 為根佈局的高度 DisplayUtils.getScreenHeight(VideoPlayerActivity.this) 螢幕的高度

root_view.post(new Runnable() {
            @Override
            public void run() {
                root_view_height = root_view.getHeight();
            }
        });