如何在build方法之外访问State类中的有状态小部件变量？

class MyWidget extends StatefulWidget {
  MyWidget({Key key}) : super(key: key);

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

class _MyWidgetState extends State<MyWidget> {
  String _text = 'Hello';

  void updateText(String newText) {
    setState(() {
      _text = newText;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        Text(_text),
        ElevatedButton(
          onPressed: () {
            setState(() {
              _text = 'World';
            });
          },
          child: Text('Change Text'),
        ),
      ],
    );
  }
}

// 在build方法之外访问有状态小部件变量
void main() {
  GlobalKey<_MyWidgetState> globalKey = GlobalKey<_MyWidgetState>();

  runApp(
    MaterialApp(
      home: Scaffold(
        body: Column(
          children: [
            MyWidget(key: globalKey),
            ElevatedButton(
              onPressed: () {
                globalKey.currentState.updateText('New Text');
              },
              child: Text('Update Text'),
            ),
          ],
        ),
      ),
    ),
  );
}