嵌套 json 对象的颤振模型
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【中文标题】嵌套 json 对象的颤振模型【英文标题】：Flutter model for nested json object 【发布时间】：2022-01-05 00:02:18 【问题描述】：我是 Flutter 的新手。我曾尝试在飞镖中开发模型类。但总是显示错误信息
Exception:type '_InternalLinkedHashMap<String, dynamic>' is not a subtype of type 'String', tt:#0 new User.fromJson
我不明白，我的代码会在哪里出错。我想要解决方案。
我想在 dart 中转换模型类。
[
"route":
"routeID": "aaaaaaaa",
"routeTitle": "bbbbbbbb"
,
"distributor":
"distributorID": "cccccccccccc",
"distributorName": "ddddddddddd"
,
"visitDate": null
]
我已经尝试过我的源代码。如下代码
import 'dart:convert';
List<User> userFromJson(String str) =>
List<User>.from(json.decode(str).map((x) => User.fromJson(x)));
String userToJson(List<User> data) =>
json.encode(List<dynamic>.from(data.map((x) => x.toJson())));
class User
User(
this.visitDate,
this.route,
this.distributor,
);
String visitDate;
String route;
String distributor;
factory User.fromJson(Map<String, dynamic> json) => User(
visitDate: json["visitDate"],
route: json["route"],
distributor: json["distributor"],
);
Map<String, dynamic> toJson() =>
"visitDate": visitDate,
"route": route,
"distributor": distributor,
;
Route RouteFromJson(String str) => Route.fromJson(json.decode(str));
String RouteToJson(Route data) => json.encode(data.toJson());
class Route
Route(
this.routeID,
this.routeTitle,
);
String routeID;
String routeTitle;
factory Route.fromJson(Map<String, dynamic> json) => Route(
routeID: json["routeID"],
routeTitle: json["routeTitle"],
);
Map<String, dynamic> toJson() =>
"routeID": routeID,
"routeTitle": routeTitle,
;
Distributor DistributorFromJson(String str) => Distributor.fromJson(json.decode(str));
String DistributorToJson(Distributor data) => json.encode(data.toJson());
class Distributor
Distributor(
this.distributorID,
this.distributorName,
);
String distributorID;
String distributorName;
factory Distributor.fromJson(Map<String, dynamic> json) => Distributor(
distributorID: json["distributorID"],
distributorName: json["distributorName"],
);
Map<String, dynamic> toJson() =>
"distributorID": distributorID,
"distributorName": distributorName,
;
如何更正我的模型类。请帮我。谢谢
【问题讨论】：
【参考方案1】：像这样改变你的用户类：
class User
User(
this.visitDate,
this.route,
this.distributor,
);
String visitDate;
Route route;
Distributor distributor;
factory User.fromJson(Map<String, dynamic> json) => User(
visitDate: json["visitDate"],
route = json['route'] != null ? Route.fromJson(json['route']) : null;
distributor = json['distributor'] != null
? Distributor.fromJson(json['distributor'])
: null;
);
Map<String, dynamic> toJson() =>
"visitDate": visitDate,
if (route != null)
data['route'] = this.route.toJson();
if (distributor != null)
data['distributor'] = this.distributor.toJson();
;
【讨论】：
【参考方案2】：您也可以查看json_serializable 包。
这样，您就不必自己编写此代码了。
https://pub.dev/packages/json_serializable
【讨论】：
【参考方案3】：这是重写模型的方法：
import 'dart:convert';
List<User> usersFromJson(String str) =>
List<User>.from(json.decode(str).map((x) => User.fromJson(x)));
String usersToJson(List<User> data) =>
json.encode(List<dynamic>.from(data.map((x) => x.toJson())));
class User
User(
required this.visitDate,
required this.route,
required this.distributor,
);
String? visitDate;
Route route;
Distributor distributor;
User.fromJson(Map<String, dynamic> json)
: visitDate = json["visitDate"],
route = Route.fromJson(json["route"]),
distributor = Distributor.fromJson(json["distributor"]);
Map<String, dynamic> toJson() =>
"visitDate": visitDate,
"route": route.toJson(),
"distributor": distributor.toJson(),
;
class Route
Route(
required this.routeID,
required this.routeTitle,
);
String routeID;
String routeTitle;
Route.fromJson(Map<String, dynamic> json)
: routeID = json["routeID"],
routeTitle = json["routeTitle"];
Map<String, dynamic> toJson() =>
"routeID": routeID,
"routeTitle": routeTitle,
;
class Distributor
Distributor(
required this.distributorID,
required this.distributorName,
);
String distributorID;
String distributorName;
Distributor.fromJson(Map<String, dynamic> json)
: distributorID = json["distributorID"],
distributorName = json["distributorName"];
Map<String, dynamic> toJson() =>
"distributorID": distributorID,
"distributorName": distributorName,
;
void main()
const data = '''[
"route":
"routeID": "aaaaaaaa",
"routeTitle": "bbbbbbbb"
,
"distributor":
"distributorID": "cccccccccccc",
"distributorName": "ddddddddddd"
,
"visitDate": null
]''';
final decoded = usersFromJson(data);
final encoded = usersToJson(decoded);
print(decoded);
print(encoded);
一些注意事项。
您似乎在使用过时的 dart 版本。我建议将项目中的 dart 版本更新为 2.14.0，这是当前最新的主要版本。您可能必须运行 flutter upgrade 才能这样做。您可以在 pubspec.yaml 文件中更改 dart 的版本。 dart 版本的设置如下所示：
environment:
sdk: ">=2.14.0 <3.0.0"
您在代码中遇到的主要问题是，在您的 User 类中，您已将 route 和 distributor 定义为 String 类型，而实际上，您希望它们为 Route 类型和Distributor。在 User 类的构造函数中，表达式 json["route"] 将返回类似 "routeID": "aaaaaaaa", "routeTitle": "bbbbbbbb" 的内容，这不是 String 而是 Map<String, dynamic>，这就是您收到上述错误消息的原因。
【讨论】：
【参考方案4】：颤振盒！
您只需要做简单的工作就是访问以下网站。并且需要将您想要转换的响应或地图/列表放入模型类中，其余将由服务器完成。
顺便说一句， 对于您的 List
// To parse this JSON data, do
//
// final routeModelClass = routeModelClassFromJson(jsonString);
import 'dart:convert';
List<RouteModelClass> routeModelClassFromJson(String str) => List<RouteModelClass>.from(json.decode(str).map((x) => RouteModelClass.fromJson(x)));
String routeModelClassToJson(List<RouteModelClass> data) => json.encode(List<dynamic>.from(data.map((x) => x.toJson())));
class RouteModelClass
RouteModelClass(
this.route,
this.distributor,
this.visitDate,
);
Route route;
Distributor distributor;
dynamic visitDate;
factory RouteModelClass.fromJson(Map<String, dynamic> json) => RouteModelClass(
route: Route.fromJson(json["route"]),
distributor: Distributor.fromJson(json["distributor"]),
visitDate: json["visitDate"],
);
Map<String, dynamic> toJson() =>
"route": route.toJson(),
"distributor": distributor.toJson(),
"visitDate": visitDate,
;
class Distributor
Distributor(
this.distributorId,
this.distributorName,
);
String distributorId;
String distributorName;
factory Distributor.fromJson(Map<String, dynamic> json) => Distributor(
distributorId: json["distributorID"],
distributorName: json["distributorName"],
);
Map<String, dynamic> toJson() =>
"distributorID": distributorId,
"distributorName": distributorName,
;
class Route
Route(
this.routeId,
this.routeTitle,
);
String routeId;
String routeTitle;
factory Route.fromJson(Map<String, dynamic> json) => Route(
routeId: json["routeID"],
routeTitle: json["routeTitle"],
);
Map<String, dynamic> toJson() =>
"routeID": routeId,
"routeTitle": routeTitle,
;
List/Map to Model class
【讨论】：
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