_TypeError（类型列表不是映射的子类型）

Question

你好，我正在做一个api调用，在那里我得到了一系列的横幅。我正在犯错误-

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

横幅。飞奔

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();
  }
}

横幅。飞奔

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_助手。飞奔

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");
    }
  }
}

得到你的横幅。飞奔

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

Answer 1

如果API的响应是一个列表，则错误是由getBanner引发的。因为fromJson方法期望类型为Map

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();
  }
}