code: public static boolean isActivityFullscreen(Activity activity)
      {
          WindowManager.LayoutParams attrs = activity.getWindow().getAttributes();
          if ((attrs.flags & WindowManager.LayoutParams.FLAG_FULLSCREEN) == WindowManager.LayoutParams.FLAG_FULLSCREEN)
          {
              return true;
          }
          else
          {
              return false;
          }
      }
docs: 判断当前activity是否为全屏
  @param activity 当前activity
  @return 是否全屏