如何在Flutter中设置showDialog()方法中的DropdownButton的值？

String selectedValue = 'Option 1';

showDialog(
  context: context,
  builder: (BuildContext context) {
    return StatefulBuilder(
      builder: (BuildContext context, StateSetter setState) {
        return AlertDialog(
          title: Text('Select an option'),
          content: DropdownButton<String>(
            value: selectedValue,
            onChanged: (String newValue) {
              setState(() {
                selectedValue = newValue;
              });
              Navigator.of(context).pop(); // 关闭对话框
            },
            items: <String>[
              'Option 1',
              'Option 2',
              'Option 3',
            ].map<DropdownMenuItem<String>>((String value) {
              return DropdownMenuItem<String>(
                value: value,
                child: Text(value),
              );
            }).toList(),
          ),
        );
      },
    );
  },
);