Flutter如何在等待返回后通过setState更新UI？

class MyWidget extends StatefulWidget {
  @override
  _MyWidgetState createState() => _MyWidgetState();
}

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

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        Text(data),
        RaisedButton(
          onPressed: () async {
            // 等待返回结果
            String result = await fetchData();
            // 更新UI
            setState(() {
              data = result;
            });
          },
          child: Text('获取数据并更新UI'),
        ),
      ],
    );
  }

  Future<String> fetchData() async {
    // 模拟获取数据的过程
    await Future.delayed(Duration(seconds: 2));
    return '返回的数据';
  }
}