我有一个文件，里面有下面的代码，我想通过导入在另一个文件中使用它，但是Map<String，dynamic> dataList的值总是为空。为什么？

import 'package:http/http.dart' as http;
import 'dart:convert';

class Structure {
  Map<String, dynamic> dataList = <String, dynamic>{};
  final String apiKey = "Dx6Raz0w6yVEEilPlk2edTmDSJBvTJh7qkou7OwW";
  String query = "Cheddar Cheese";
  String dataType = "SR Legacy";
  String pageSize = "25";
  String pageNumber = "2";
  String sortBy = "publishedDate";
  String sortOrder = "asc";

  Future<void> readData() async {
    query.replaceAll(' ', '%20');
    dataType.replaceAll(' ', '%20');
    String request =
        "https://api.nal.usda.gov/fdc/v1/foods/search?query=$query&dataType=$dataType&pageSize=$pageSize&pageNumber=$pageNumber&sortBy=$sortBy&sortOrder=$sortOrder&api_key=$apiKey";

    final response = await http.get(Uri.parse(request));

    if (response.statusCode == 200) {
      Map<String, dynamic> data = jsonDecode(response.body);
      dataList = data;
    } else {
      throw Exception('Failed to fetch data');
    }
  }
}

字符串
然后在我尝试的另一个文件中：

Structure s = Structure();
s.readData();
print('$s.dataList');

型
我也试过：

Structure s = Structure();
setState(() {s.readData();});
print('$s.dataList');

型
但是dataList总是空的，为什么？