_TypeError（类型'List<dynamic>'不是'Map<String，dynamic>'类型的子类型）

Posted 2023-02-23

【中文标题】_TypeError（类型\'List<dynamic>\'不是\'Map<String，dynamic>\'类型的子类型）

【英文标题】：_TypeError (type 'List<dynamic>' is not a subtype of type 'Map<String, dynamic>') in flutter_TypeError（类型'List<dynamic>'不是'Map<String，dynamic>'类型的子类型）

【发布时间】：2021-09-12 06:46:30

【问题描述】：

您好，我正在进行 api 调用，我正在获取横幅数组。我遇到了错误-

_TypeError (type 'List<dynamic>' is not a subtype of type 'Map<String, dynamic>')

banners_bloc.dart

class BannersBloc 
  late BannerRepository _bannerRepository;
  late StreamController _streamController;

  StreamSink get bannerListSink => _streamController.sink;

  BannersBloc() 
    _streamController = StreamController();
    _bannerRepository = BannerRepository();
    fetchBanners();
  

  fetchBanners() async 
    bannerListSink.add('Fetching Banners');
    try 
      Banners banners = await _bannerRepository.getBanners();
      bannerListSink.add(banners);
     catch (e) 
      bannerListSink.add(e.toString());
      print(e);
    
  

  dispose() 
    _streamController.close();
  

banners.dart

class Banners 
  late String bannerImageUrl;
  late String bannerImageAlt;
  late bool isActive;
  late int order;
  late String id;

  Banners(
      required this.bannerImageUrl,
      required this.bannerImageAlt,
      required this.isActive,
      required this.order,
      required this.id);

  Banners.fromJson(Map<String, dynamic> json) 
    bannerImageUrl = json['bannerImageUrl'];
    bannerImageAlt = json['bannerImageAlt'];
    isActive = json['isActive'];
    order = json['order'];
    id = json['id'];
  

  Map<String, dynamic> toJson() 
    final Map<String, dynamic> data = new Map<String, dynamic>();
    data['bannerImageUrl'] = this.bannerImageUrl;
    data['bannerImageAlt'] = this.bannerImageAlt;
    data['isActive'] = this.isActive;
    data['order'] = this.order;
    data['id'] = this.id;
    return data;
  

api_base_helper.dart

class APIHelper 
  final String _baseURL =
      "https://raw.githubusercontent.com/gautam-in/shopping-cart-assignment/master/server/";

  Future<dynamic> get(String url) async 
    try 
      final response = await http.get(Uri.parse(_baseURL + url));
      return json.decode(response.body);
     catch (err) 
      throw new Exception("Something went wrong");
    
  

get_banners.dart

class BannerRepository 
  Future getBanners() async 
    final response = await new APIHelper().get("banners/index.get.json");
    return Banners.fromJson(response);
  

【问题讨论】：

这能回答你的问题吗？ Error: List<dynamic> is not a subtype of type Map<String, dynamic>

【参考方案1】：

如果您的 API 响应是横幅列表，则错误是由 getBanners 引发的。因为fromJson 方法需要Map<String, dynamic> 类型。要解决此问题，您需要遍历响应并为响应列表中的每个项目调用 Banners.fromJson。

class BannerRepository 
  Future<List<Banners>> getBanners() async 
    final response = await new APIHelper().get("banners/index.get.json");
   // Sample Code, handler errors and other stuff
    return response.map((e) =>Banners.fromJson(e)).toList();
  

【讨论】：

您的错误来自哪里？粘贴完整的错误，以便我们可以正确追踪错误

这一行返回 response.map((e) => Banners.fromJson(response)).toList();颤振：类型 'List' 不是类型 'Map'

的子类型

我的错误，应该是e 而不是response。更新了代码块

现在迭代此地图后，将流向 fromJson 中的 pojo 类，然后在迭代后给出相同的错误。

更新您的问题，包括确切的行号和发生错误的文件。