当使用futurebuilder提供groupValue时，无法在UI中选择单选按钮

import 'package:flutter/material.dart';

class RadioButtonGroup extends StatefulWidget {
  @override
  _RadioButtonGroupState createState() => _RadioButtonGroupState();
}

class _RadioButtonGroupState extends State<RadioButtonGroup> {
  String selectedValue;

  @override
  Widget build(BuildContext context) {
    return FutureBuilder<String>(
      future: fetchData(), // 异步操作，返回一个Future<String>
      builder: (context, snapshot) {
        if (snapshot.connectionState == ConnectionState.waiting) {
          return CircularProgressIndicator(); // 正在加载数据时显示加载指示器
        } else if (snapshot.hasError) {
          return Text('Error: ${snapshot.error}'); // 加载数据出错时显示错误信息
        } else {
          // 异步操作完成后更新selectedValue的值
          selectedValue = snapshot.data;

          return Column(
            children: [
              RadioListTile(
                title: Text('Option 1'),
                value: 'option1',
                groupValue: selectedValue,
                onChanged: (value) {
                  setState(() {
                    selectedValue = value;
                  });
                },
              ),
              RadioListTile(
                title: Text('Option 2'),
                value: 'option2',
                groupValue: selectedValue,
                onChanged: (value) {
                  setState(() {
                    selectedValue = value;
                  });
                },
              ),
            ],
          );
        }
      },
    );
  }

  Future<String> fetchData() async {
    // 执行异步操作，返回一个String类型的结果
    await Future.delayed(Duration(seconds: 2)); // 模拟异步操作的延迟
    return 'option1'; // 假设异步操作返回'option1'
  }
}