问题：

列表视图中的Flutter显示嵌套json返回类型String不是类型强制转换中的Map类型的子类型

白博易

2023-03-14

我要在颤栗中继续我的旅程。我能够在ListView中显示一个简单的json。现在我尝试使用带有嵌套对象的json，但每次运行应用程序时都会出现错误

我正在为json模型类生成代码，如颤振官方文档中建议的那样。

这个错误似乎是在我分析用户时发生的。在调试时，我看到名称和姓氏被成功解析，但当我跳转到user中的details对象时。g、在行中省道：

json['details'] == null
        ? null
        : Details.fromJson(json['details'] as Map<String, dynamic>),

我看到错误：

type String is not a subtype of type 'Map<String, dynamic>' in type cast

如何解决此错误，以及如何访问所有嵌套对象以显示它们？

这是我要解析的json。我编辑了一下，没有arename字段：

数据json

[
    {
        "name": "jhon",
        "surname": "walker",
        "details": "{\"work\":{\"salary\":\"116\",\"company\":\"evolution\"},\"address\":{\"street\":\"grand station\",\"city\":\"salt lake\"}}"    
    },
    {
        "name": "peter",
        "surname": "parker",
        "details": "{\"work\":{\"salary\":\"116\",\"company\":\"evolution\"},\"address\":{\"street\":\"grand station\",\"city\":\"salt lake\"}}"    
    }
]

这里有我的模型类：

user.dart

import 'package:json_annotation/json_annotation.dart';
import 'details.dart';

part 'user.g.dart';

@JsonSerializable(explicitToJson: true)
class User {
  User(this.name, this.surname, this.details);

  String name;
  String surname;
  Details details;

  factory User.fromJson(Map<String, dynamic> json) => _$UserFromJson(json);
  Map<String, dynamic> toJson() => _$UserToJson(this);
}

使用者g、飞镖

// GENERATED CODE - DO NOT MODIFY BY HAND

part of 'user.dart';

// **************************************************************************
// JsonSerializableGenerator
// **************************************************************************

User _$UserFromJson(Map<String, dynamic> json) {
  return User(
    json['name'] as String,
    json['surname'] as String,
    json['details'] == null
        ? null
        : Details.fromJson(json['details'] as Map<String, dynamic>),
  );
}

Map<String, dynamic> _$UserToJson(User instance) => <String, dynamic>{
      'name': instance.name,
      'surname': instance.surname,
      'details': instance.details?.toJson(),
    };

细节。飞奔

import 'package:json_annotation/json_annotation.dart';
import 'address.dart';
import 'work.dart';
part 'details.g.dart';

@JsonSerializable(explicitToJson: true)
class Details {
  Details(this.work, this.address);

  Work work;
  Address address;

  factory Details.fromJson(Map<String, dynamic> json) =>
      _$DetailsFromJson(json);
  Map<String, dynamic> toJson() => _$DetailsToJson(this);
}

details.g.dart

// GENERATED CODE - DO NOT MODIFY BY HAND

part of 'details.dart';

// **************************************************************************
// JsonSerializableGenerator
// **************************************************************************

Details _$DetailsFromJson(Map<String, dynamic> json) {
  return Details(
    json['work'] == null
        ? null
        : Work.fromJson(json['work'] as Map<String, dynamic>),
    json['address'] == null
        ? null
        : Address.fromJson(json['address'] as Map<String, dynamic>),
  );
}

Map<String, dynamic> _$DetailsToJson(Details instance) => <String, dynamic>{
      'work': instance.work?.toJson(),
      'address': instance.address?.toJson(),
    };

工作飞奔

import 'package:json_annotation/json_annotation.dart';
part 'work.g.dart';

@JsonSerializable(explicitToJson: true)
class Work {
  Work(this.salary, this.company);

  String salary;
  String company;

  factory Work.fromJson(Map<String, dynamic> json) => _$WorkFromJson(json);
  Map<String, dynamic> toJson() => _$WorkToJson(this);
}

工作g、飞镖

// GENERATED CODE - DO NOT MODIFY BY HAND

part of 'work.dart';

// **************************************************************************
// JsonSerializableGenerator
// **************************************************************************

Work _$WorkFromJson(Map<String, dynamic> json) {
  return Work(
    json['salary'] as String,
    json['company'] as String,
  );
}

Map<String, dynamic> _$WorkToJson(Work instance) => <String, dynamic>{
      'salary': instance.salary,
      'company': instance.company,
    };

住址飞奔

import 'package:json_annotation/json_annotation.dart';
part 'address.g.dart';

@JsonSerializable(explicitToJson: true)
class Address {
  Address(this.street, this.city);
  
  String street;
  String city;

  factory Address.fromJson(Map<String, dynamic> json) =>
      _$AddressFromJson(json);
  Map<String, dynamic> toJson() => _$AddressToJson(this);
}

address.g.dart

// GENERATED CODE - DO NOT MODIFY BY HAND

part of 'address.dart';

// **************************************************************************
// JsonSerializableGenerator
// **************************************************************************

Address _$AddressFromJson(Map<String, dynamic> json) {
  return Address(
    json['street'] as String,
    json['city'] as String,
  );
}

Map<String, dynamic> _$AddressToJson(Address instance) => <String, dynamic>{
      'street': instance.street,
      'city': instance.city,
    };

最后，这里还有应用：main.dart

import 'package:flutter/material.dart';
import 'dart:convert';
import 'package:http/http.dart' as http;
import 'user.dart';
import 'details.dart';
import 'address.dart';
import 'work.dart';
import 'package:built_value/serializer.dart';
import 'dart:convert' as json;
import 'package:meta/meta.dart';
import 'package:built_value/built_value.dart';
import 'package:built_collection/built_collection.dart';
import 'dart:developer';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        // This is the theme of your application.
        //
        // Try running your application with "flutter run". You'll see the
        // application has a blue toolbar. Then, without quitting the app, try
        // changing the primarySwatch below to Colors.green and then invoke
        // "hot reload" (press "r" in the console where you ran "flutter run",
        // or simply save your changes to "hot reload" in a Flutter IDE).
        // Notice that the counter didn't reset back to zero; the application
        // is not restarted.
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  // This widget is the home page of your application. It is stateful, meaning
  // that it has a State object (defined below) that contains fields that affect
  // how it looks.

  // This class is the configuration for the state. It holds the values (in this
  // case the title) provided by the parent (in this case the App widget) and
  // used by the build method of the State. Fields in a Widget subclass are
  // always marked "final".

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;


  Future<List<User>> getUsers() async {
    var url = "empty for now"; // here there will be the request now I' m using fake data
    //final response = await http.get(url);
    //final parsed = json.decode(response.body).cast<Map<String, dynamic>>();
    String data = r'''[
      {
        "name": "260",
        "surname": "430011",
        "areaName": "Camera1-Zone1",
        "details": "{\"work\":{\"salary\":\"116\",\"company\":\"evolution\"},\"address\":{\"street\":\"grand station\",\"city\":\"salt lake\"}}"
      },
      {
        "name": "260",
        "surname": "430011",
        "areaName": "Camera1-Zone1",
        "details": "{\"work\":{\"salary\":\"116\",\"company\":\"evolution\"},\"address\":{\"street\":\"grand station\",\"city\":\"salt lake\"}}"
      }
    ]''';
    final parsed = json.jsonDecode(data).cast<Map<String, dynamic>>();
    return parsed.map<User>((json) {
      return User.fromJson(json);
    }).toList();
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text("List"),
          backgroundColor: Colors.blue,
        ),
        body: Container(
          child: FutureBuilder<List<User>>(
            future: getUsers(),
            builder: (context, snapshot) {
              if (snapshot.hasData) {
                return ListView.builder(
                  itemCount: snapshot.data.length,
                  itemBuilder: (context, int index) {
                    return ListTile(
                        title: Text(snapshot.data[index].name),
                        subtitle: Text(snapshot.data[index].surname));
                  },
                );
              } else if (snapshot.hasError) {
                return Center(
                  child: Text(snapshot.error.toString()),
                );
              }
              return Center(
                child: CircularProgressIndicator(),
              );
            },
          ),
        ),
      ),
    );
  }
}

你能帮我解决这个错误并显示所有嵌套数据吗？谢谢你！

谢谢你的帮助！

共有2个答案

邹高懿

2023-03-14

我找到一个解决办法。

我使用的模型是：

模型飞奔

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.name,
    this.surname,
    this.areaName,
    this.details,
  });

  String name;
  String surname;
  String areaName;
  String details;

  factory User.fromJson(Map<String, dynamic> json) => User(
        name: json["name"],
        surname: json["surname"],
        areaName: json["areaName"],
        details: json["details"],
      );

  Map<String, dynamic> toJson() => {
        "name": name,
        "surname": surname,
        "areaName": areaName,
        "details": details,
      };
}

Details DetailsFromJson(String str) => Details.fromJson(json.decode(str));

String DetailsToJson(Details data) => json.encode(data.toJson());

class Details {
  Details({
    this.work,
    this.address,
  });

  Work work;
  Address address;

  factory Details.fromJson(Map<String, dynamic> json) => Details(
        work: Work.fromJson(json["work"]),
        address: Address.fromJson(json["address"]),
      );

  Map<String, dynamic> toJson() => {
        "work": work.toJson(),
        "address": address.toJson(),
      };
}

class Address {
  Address({
    this.street,
    this.city,
  });

  String street;
  String city;

  factory Address.fromJson(Map<String, dynamic> json) => Address(
        street: json["street"],
        city: json["city"],
      );

  Map<String, dynamic> toJson() => {
        "street": street,
        "city": city,
      };
}

class Work {
  Work({
    this.salary,
    this.company,
  });

  String salary;
  String company;

  factory Work.fromJson(Map<String, dynamic> json) => Work(
        salary: json["salary"],
        company: json["company"],
      );

  Map<String, dynamic> toJson() => {
        "salary": salary,
        "company": company,
      };
}

主代码是：main。飞奔

import 'package:flutter/material.dart';
import 'dart:convert';
import 'package:http/http.dart' as http;
import 'user.dart';
import 'details.dart';
import 'address.dart';
import 'work.dart';
import 'package:built_value/serializer.dart';
import 'dart:convert' as json;
import 'package:meta/meta.dart';
import 'package:built_value/built_value.dart';
import 'package:built_collection/built_collection.dart';
import 'dart:developer';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        // This is the theme of your application.
        //
        // Try running your application with "flutter run". You'll see the
        // application has a blue toolbar. Then, without quitting the app, try
        // changing the primarySwatch below to Colors.green and then invoke
        // "hot reload" (press "r" in the console where you ran "flutter run",
        // or simply save your changes to "hot reload" in a Flutter IDE).
        // Notice that the counter didn't reset back to zero; the application
        // is not restarted.
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  // This widget is the home page of your application. It is stateful, meaning
  // that it has a State object (defined below) that contains fields that affect
  // how it looks.

  // This class is the configuration for the state. It holds the values (in this
  // case the title) provided by the parent (in this case the App widget) and
  // used by the build method of the State. Fields in a Widget subclass are
  // always marked "final".

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;


  Future<List<User>> getUsers() async {
    var url = "empty for now"; // here there will be the request now I' m using fake data
    //final response = await http.get(url);
    //final parsed = json.decode(response.body).cast<Map<String, dynamic>>();
    String data = r'''[
      {
        "name": "260",
        "surname": "430011",
        "areaName": "Camera1-Zone1",
        "details": "{\"work\":{\"salary\":\"116\",\"company\":\"evolution\"},\"address\":{\"street\":\"grand station\",\"city\":\"salt lake\"}}"
      },
      {
        "name": "260",
        "surname": "430011",
        "areaName": "Camera1-Zone1",
        "details": "{\"work\":{\"salary\":\"116\",\"company\":\"evolution\"},\"address\":{\"street\":\"grand station\",\"city\":\"salt lake\"}}"
      }
    ]''';
    List<User> users= userFromJson(res);
    return users;
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text("List"),
          backgroundColor: Colors.blue,
        ),
        body: Container(
          child: FutureBuilder<List<User>>(
            future: getUsers(),
            builder: (context, snapshot) {
              if (snapshot.hasData) {
                return ListView.builder(
                  itemCount: snapshot.data.length,
                  itemBuilder: (context, int index) {
                    return ListTile(
                        title: Text(snapshot.data[index].name),
                        subtitle: Text(snapshot.data[index].surname));
                  },
                );
              } else if (snapshot.hasError) {
                return Center(
                  child: Text(snapshot.error.toString()),
                );
              }
              return Center(
                child: CircularProgressIndicator(),
              );
            },
          ),
        ),
      ),
    );
  }
}

彭骏

2023-03-14

 Future<List<User>> getUsers() async {
    var url = "empty for now"; 
   final response = await http.get(url);

     if (response.isEmpty) return null;


    Map<String, dynamic> data = json.decode(response);

    List<dynamic> list = data['data'];

     List<User> result =
     list.map((f) => User.fromJson(f)).toList();

    return result;
  }

如果json数据是这样的--

   {
    "name": "260",
    "surname": "430011",
    "areaName": "Camera1-Zone1",
    "details": {"work":{"salary":"116","company":"evolution"},"address": 
      {"street":"grand station","city":"salt lake"}}
  },

您的模型如下所示：

 import 'dart:convert';
  User userFromJson(String str) => User.fromJson(json.decode(str));

  String userToJson(User data) => json.encode(data.toJson());

 class User {
  User({
    this.name,
    this.surname,
    this.areaName,
    this.details,
 });

String name;
String surname;
String areaName;
Details details;

 factory User.fromJson(Map<String, dynamic> json) => User(
    name: json["name"],
    surname: json["surname"],
    areaName: json["areaName"],
    details: Details.fromJson(json["details"]),
 );

 Map<String, dynamic> toJson() => {
    "name": name,
    "surname": surname,
    "areaName": areaName,
    "details": details.toJson(),
 };
}

class Details {
 Details({
    this.work,
    this.address,
 });

 Work work;
 Address address;

  factory Details.fromJson(Map<String, dynamic> json) => Details(
     work: Work.fromJson(json["work"]),
    address: Address.fromJson(json["address"]),
  );

  Map<String, dynamic> toJson() => {
    "work": work.toJson(),
    "address": address.toJson(),
   };
  }

  class Address {
  Address({
    this.street,
    this.city,
  });

String street;
String city;

factory Address.fromJson(Map<String, dynamic> json) => Address(
    street: json["street"],
    city: json["city"],
);

Map<String, dynamic> toJson() => {
    "street": street,
    "city": city,
  };
 }

class Work {
Work({
    this.salary,
     this.company,
});

String salary;
String company;

 factory Work.fromJson(Map<String, dynamic> json) => Work(
    salary: json["salary"],
    company: json["company"],
 );

  Map<String, dynamic> toJson() => {
    "salary": salary,
     "company": company,
   };
  }

或者如果这样：

   {
    "name": "260",
    "surname": "430011",
    "areaName": "Camera1-Zone1",
    "details": "{\"work\": 
  {\"salary\":\"116\",\"company\":\"evolution\"},\"address\": 
   {\"street\":\"grand station\",\"city\":\"salt lake\"}}"
   }

您的模型如下所示：

import 'dart:convert';

User userFromJson(String str) => User.fromJson(json.decode(str));

String userToJson(User data) => json.encode(data.toJson());

class User {
 User({
    this.name,
    this.surname,
    this.areaName,
    this.details,
});

String name;
String surname;
String areaName;
String details;

factory User.fromJson(Map<String, dynamic> json) => User(
    name: json["name"],
    surname: json["surname"],
    areaName: json["areaName"],
    details: json["details"],
);

Map<String, dynamic> toJson() => {
    "name": name,
    "surname": surname,
    "areaName": areaName,
    "details": details,
 };
}

类似资料：

类型'String'不是类型强制转换中的类型'Map'的子类型

当我点击我的颤振应用程序中的一个按钮时，我出现了一个错误。这里有人有解决方案吗？！路线争论还有地图完全错误生成CategoryMalsScreen（脏，依赖项：[[U ModalScopeStatus]，状态：[U CategoryMalsScreenState]时引发了以下错误：类型“String”不是类型“Map”的子类型导致错误的相关小部件是：CategoryMalsScreen
列表不是类型转换中列表类型的子类型

我试图创建动态下拉，其值是从使用微服务的查找表之一填充，但我已经尝试了许多方式相同，到目前为止，我还没有成功地使其工作。下面的代码用于调用webservice 这是我的对象类型仅用于显示目前运行的以下代码我做了什么我尝试调用webservice在多种方式调用它，尝试铸造服务响应直接使用JSON字符串响应和可能的事情我尝试过。你能在这里帮忙吗？我们将不胜感激。
类型列表不是“Map类型”的子类型

我试图从API获取数据。我得到了错误类型列表不是地图的子类型。我是新来的，不明白我在哪里犯了错误。这是我的回帖功能：在我的主屏幕中，我使用了一个，如下所示：如何解决此错误？提前谢谢。
类型“\u InternalLinkedHashMap”不是类型转换中“String”类型的子类型

我试图将一个嵌套的JSON对象发布到API。下面是我正在尝试的简单代码。我收到错误消息：
“\u InternalLinkedHashMap”不是类型转换中“Map”类型的子类型

我有这个通用函数：我这样称呼它：但是，由于我将使用get_存储框作为我的_数据客户端，改为使用配置单元框，因此出现以下错误：配置单元必须以不同的格式存储数据，这可能是由于加密造成的，但如何解释这一点并消除此错误？
类型列表不是类型转换中映射类型的子类型

我在尝试使用JSON_serializable序列化从internet获取的复杂JSON并使用FutureProvider将它们连接在一起时遇到了这个问题。这是json文件，这是包含序列化类的代码，获取json文件并将其转换为dart的未来提供者，这是基因编码，这是转换后的json文件显示的代码当我试着运行这个项目时，我遇到了这个错误 i/flutter（23347）： type'Lis

列表视图中的Flutter显示嵌套json返回类型String不是类型强制转换中的Map类型的子类型

共有2个答案

相关问答

相关文章

相关阅读

相关工具

相关文档