在状态变量未更改时更改Flutter有状态窗口小部件的最终窗口小部件变量的原因

Question

请考虑以下代码段：

class CustomStateFulWidget extends StatefulWidget {
  final GlobalKey<NavigatorState> navigatorKeyFinal =  GlobalKey();

  @override
  _CustomStateFulWidget createState() => _CustomStateFulWidget();
}

class _CustomStateFulWidget extends State<CustomStateFulWidget> {
  GlobalKey<NavigatorState> navigatorKeyLocal = GlobalKey();

  @override
  Widget build(BuildContext context) {
    print("Navigator key local: ${navigatorKeyLocal.hashCode}");
    print("Navigator key final: ${widget.navigatorKeyFinal.hashCode}");

    return Center();
  }
}

在上面的代码中，每次调用 _CustomStateFulWidget 的 build方法时，navigatorKeyFinal变量值都会更改，但是navigatorKeyLocal变量保持不变。谁能解释我这种行为的原因？