flutter 遇到 for 循环报错 Expected a class member，看不懂是什么原因?

Question

最近在学flutter，自己正捣鼓一些代码，写了如下几行

class _TabPageState extends State<TabPage>{
  
  final _defaultColor = Colors.grey;
  final _activeColor = Colors.blue;
  int _currentIndex = 0;
  final PageController _controller = PageController(
    initialPage: 0
  );

  List<_TabPage> tabs = [
    _TabPage("首页", const HomePage(), Icons.home),
    _TabPage("我的", const UserPage(), Icons.account_circle),
  ];
  late List<BottomNavigationBarItem> arr =[];

  for (var i = 0; i < tabs.length; i++) {
    _TabPage tab = tabs[i];
    arr.add(BottomNavigationBarItem(
      icon: Icon(
        tab.icon,
        color: _defaultColor,
      ),
      activeIcon: Icon(
        tab.icon,
        color: _activeColor,
      ),
      label: tab.label,
    ));
  }

在for遍历那一行给我报了一个看不懂的错，我寻思没写错呀~~，苦恼...，为什么呀？

Expected a class member.
Try placing this code inside a class member. dart (expected class member)

Answer 1

要把for写到函数里面, 或者写到initState里面