flutter 错误：列表< dynamic>不是Map〈String，dynamic>类型的子类型

tktrz96b 于 2022-11-25 发布在 Flutter

关注(0)|答案(7)|浏览(275)

我目前正在构建一个通过API读取数据的应用程序，并尝试从JSON占位符解析JSON API。
我为用户创建了一个模型类（users_future_model.dart）：

class Users {
  final int userID;
  final String name;
  final String username;
  final String email;
  final Address address;

  Users({this.userID, this.name, this.username, this.email, this.address});

  factory Users.fromJson(Map<String, dynamic> usersjson)=> Users(
      userID: usersjson["id"],
      name: usersjson["name"],
      username: usersjson["username"],
      email: usersjson["email"],
      address: Address.fromJson(usersjson["address"])
  );
}

class Address{

  final String street;
  final String suite;
  final String city;
  final String zipcode;

  Address({this.street, this.suite, this.city, this.zipcode});

  factory Address.fromJson(Map<String, dynamic> addjson){

    return Address(
      street: addjson["street"],
      suite:  addjson["suite"],
      city: addjson["city"],
      zipcode: addjson["zipcode"]
    );
  }
}

这是main.dart将json读入小部件：

import 'package:flutter/material.dart';
import 'model/users_future_model.dart';
import 'dart:convert';
import 'dart:async';
import 'package:http/http.dart' as http;

final String jsonplaceholder = "http://jsonplaceholder.typicode.com/users/";

//Future method to read the URL
Future<Users> fetchInfo() async{
  final response = await http.get(jsonplaceholder);
  final jsonresponse = json.decode(response.body);

  return Users.fromJson(jsonresponse);
}

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      home: new MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => new _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text("Parse JSON"),
      ),
      body: new Center(
        child: new Column(
          children: <Widget>[
            new FutureBuilder(
                future: fetchInfo(),
                builder: (context, snapshot){
                  if(snapshot.hasData){
                    return new Text(snapshot.data.email);
                  }else if(snapshot.hasError){
                    return new Text("Error ${snapshot.error}");
                  }
                })
          ],
        ),
      )
    );
  }
}

这是我尝试读取的JSON信息，尽管它只是其中的一小部分：

{
id: 1,
name: "Leanne Graham",
username: "Bret",
email: "Sincere@april.biz",
address: {
 street: "Kulas Light",
 suite: "Apt. 556",
 city: "Gwenborough",
 zipcode: "92998-3874",
 geo: {
  lat: "-37.3159",
  lng: "81.1496"
 }
},
phone: "1-770-736-8031 x56442",
website: "hildegard.org",
company: {
 name: "Romaguera-Crona",
 catchPhrase: "Multi-layered client-server neural-net",
 bs: "harness real-time e-markets"
}
}

我目前遇到的错误是：

Error type 'List<dynamic>' is not a subtype of type 'Map<String, dynamic>'

如何更正此错误？

flutter

来源：https://stackoverflow.com/questions/51854891/error-listdynamic-is-not-a-subtype-of-type-mapstring-dynamic

7条答案

按热度按时间

mm5n2pyu1#

API返回JSON数组而不是json对象，因此是List而不是Map。
即用户json是Json数组得第一个元素。
因此，要获取第一个元素，请使用第一个索引。
return Users.fromJson(jsonresponse[0]);

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2guxujil2#

var streetsFromJson = parsedJson['streets'];
List<String> streetsList = new List<String>.from(streetsFromJson);

Thnx适用于https://medium.com/flutter-community/parsing-complex-json-in-flutter-747c46655f51

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0kjbasz63#

查看此答案

Future<List<ProductList>> getProductList() async {
  print("comes");
  String productURl= mainURL+'api/store/product-with-category/';

  final response = await http.get(productURl,headers:{"Content-Type": 
 "application/json"});
  List jsonResponse = json.decode(response.body);
  return jsonResponse.map((job) => new ProductList.fromJson(job)).toList();
  
}

获取函数

FutureBuilder<List<ProductList>>(
    future: getProductList(),
    builder: (context, snapshot) {
      print("snapshot");
      print(snapshot.data);
      if (snapshot.hasData) {
        return Padding(
          padding: const EdgeInsets.all(8.0),
          child: GridView.builder(
          itemCount: snapshot.data.length,
            gridDelegate:SliverGridDelegateWithFixedCrossAxisCount( crossAxisCount: 2,),
            itemBuilder:  (BuildContext context, int i){
              return Card(
                child: Container(
                  decoration: BoxDecoration(
                      border: Border.all(width: 0.5,color: Colors.grey)
                  ),
                  child: Padding(
                    padding: const EdgeInsets.all(8.0),
                    child: Column(
                      children: <Widget>[
                         text18(snapshot.data[i].title, Colors.black, FontWeight.bold)
                      ],
                    ),
                  ),
                ),
              );
            }
        )
        );
      } else if (snapshot.hasError) {
        return Text("${snapshot.error}");
      }

      // By default, show a loading spinner.
      return CircularProgressIndicator();
    },
  ),

只需更改URL并创建模型类

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n53p2ov04#

只是注意错误

List<dynamic> is not a subtype of type Map<String, dynamic>

基本上，这意味着您在点击Web服务后接收到的数据是列表形式的，但您使用的内部数据类是Map类型的。因此，由于结构不匹配，无法解析数据，因为Map在中定义，而不是数据类中的List。

重新检查Json响应和相应的PODO类

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o4tp2gmn5#

另一种轻松实现此目的的方法：

import 'package:json_helpers/json_helpers.dart';

void main() {
  // If request returns list of users
  var body = '[{"id": 1}, {"id": 2} ]';
  final users = body.jsonList((e) => User.fromJson(e));
  assert(users[1].id == 2);
  print(users[1].id);

  // If request returns the user
  body = '{"id": 1}';
  final user = body.json((e) => User.fromJson(e));
  assert(user.id == 1);
  print(user.id);
}

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uurity8g6#

import 'dart:convert';
List<User> userFromJson(String str) => List<User>.from(json.decode(str).map((x) => User.fromJson(x)));
class User {
  int? id;
  String? name;
  String? username;
  String? email;
  Address? address;
  String? phone;
  String? website;
  Company? company;
  factory User.fromJson(Map<String, dynamic> json) => User(
    id: json["id"],
    name: json["name"],
    username: json["username"],
    email: json["email"],
    //   address =
    //   json['address'] != null ? Address.fromJson(json['address']) : null;
    address :Address.fromJson(json['address']),// chua check null
    phone: json["phone"],
    website: json["website"],
    company :Company.fromJson(json['company']),// chua check null
  );
  User({
    required this.id,
    required this.name,
    required this.username,
    required this.email,
    required this.address,
    required this.phone,
    required this.website,
    required this.company,
  });

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data =  <String, dynamic>{};
    data['id'] = id;
    data['name'] = name;
    data['username'] = username;
    data['email'] = email;
    if (address != null) {
      data['address'] = address!.toJson();
    }
    data['phone'] = phone;
    data['website'] = website;
    if (company != null) {
      data['company'] = company!.toJson();
    }
    return data;
  }
}

class Address {
  String? street;
  String? suite;
  String? city;
  String? zipcode;
  Geo? geo;

  Address({this.street, this.suite, this.city, this.zipcode, this.geo});

  Address.fromJson(Map<String, dynamic> json) {
    street = json['street'];
    suite = json['suite'];
    city = json['city'];
    zipcode = json['zipcode'];
    geo = json['geo'] != null ? Geo.fromJson(json['geo']) : null;
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = <String, dynamic>{};
    data['street'] = street;
    data['suite'] = suite;
    data['city'] = city;
    data['zipcode'] = zipcode;
    if (geo != null) {
      data['geo'] = geo!.toJson();
    }
    return data;
  }
}

class Geo {
  String? lat;
  String? lng;

  Geo({this.lat, this.lng});

  Geo.fromJson(Map<String, dynamic> json) {
    lat = json['lat'];
    lng = json['lng'];
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = <String, dynamic>{};
    data['lat'] = lat;
    data['lng'] = lng;
    return data;
  }
}

class Company {
  String? name;
  String? catchPhrase;
  String? bs;

  Company({this.name, this.catchPhrase, this.bs});

  Company.fromJson(Map<String, dynamic> json) {
    name = json['name'];
    catchPhrase = json['catchPhrase'];
    bs = json['bs'];
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = <String, dynamic>{};
    data['name'] = name;
    data['catchPhrase'] = catchPhrase;
    data['bs'] = bs;
    return data;
  }
}

import 'dart:core';
import 'package:demo_user_api_http/models/user.dart';
import 'package:http/http.dart' as http;

class RemoteService{
  Future<List<User>?> getUsers() async{
    var client = http.Client();

    var uri = Uri.parse('https://jsonplaceholder.typicode.com/users');
    var response = await client.get(uri);
    if (response.statusCode == 200) {
      var json = response.body;
      return userFromJson(json);
    }
    return null;
  }

List<User>? users;
  var isLoaded = false;
  @override
  void initState() {
    super.initState();
    getData();
  }
  getData() async {
    users = await RemoteService().getUsers();
    if (users != null) {
      setState(() {
        isLoaded = true;
      });
    }
  }

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gajydyqb7#

用途

List<dynamic> output = jsonDecode(yourJsonSource);

代替

Map<String, dynamic> output = jsonDecode(yourJsonSource);

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我来回答

flutter 错误：列表< dynamic>不是Map〈String，dynamic>类型的子类型

7条答案

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