未处理的异常：类型'_InternalLinkedHashMap <String，dynamic>'不是类型转换中类型'List <dynamic>'的子类型吗？

Question

这是答复

{
"overview": "A ticking-time-bomb insomniac and a slippery soap salesman channel primal male aggression into a shocking new form of therapy. Their concept catches on, with underground "fight clubs" forming in every town, until an eccentric gets in the way and ignites an out-of-control spiral toward oblivion.",
"title": "Fight Club",
}

模型

class Movies {
  String title;
  String overview;
  

  Movies(
      {this.title , this.overview});

      factory Movies.fromJson(Map <String, dynamic> parsedJson){
        return Movies(title: parsedJson['title'] , overview: parsedJson['overview']);
      }

}

和

  Future <List<Movies>> fetchMovies () async {
    var response = await http.get(url);
    var jsonData = jsonDecode(response.body) as List ;
    List<Movies> movies = jsonData.map((e) => Movies.fromJson(e)).toList();
    
    print(movies.length);
    return movies;

  }

无论我做什么，都会收到此错误（未处理的异常：类型'_InternalLinkedHashMap '不是类型转换中'List'类型的子类型）

Answer 1

您尝试将jsonData转换为List，但是解码器说它的类型为Map（也显示为Map类型）

Future <List<Movies>> fetchMovies () async {
  var response = await http.get(url);
  var jsonData = jsonDecode(response.body);
  if(jsonData is List) //check if it's a List
    return List<Movies>.from(jsonData.map(map) => Movies.fromJson(map));
  else if(jsonData is Map) //check if it's a Map
    return [Movies.fromJson(jsonData)]; //return a List of length 1

}

Answer 2

您可以在下面复制粘贴运行完整代码
您可以使用moviesFromJson并与FutureBuilder一起显示
代码段

List<Movies> moviesFromJson(String str) =>
    List<Movies>.from(json.decode(str).map((x) => Movies.fromJson(x)));
    
if (response.statusCode == 200) {
      return moviesFromJson(jsonString);

工作演示

完整代码

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

List<Movies> moviesFromJson(String str) =>
    List<Movies>.from(json.decode(str).map((x) => Movies.fromJson(x)));

String moviesToJson(List<Movies> data) =>
    json.encode(List<dynamic>.from(data.map((x) => x.toJson())));

class Movies {
  Movies({
    this.overview,
    this.title,
  });

  String overview;
  String title;

  factory Movies.fromJson(Map<String, dynamic> json) => Movies(
        overview: json["overview"],
        title: json["title"],
      );

  Map<String, dynamic> toJson() => {
        "overview": overview,
        "title": title,
      };
}

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

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

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;
  Future<List<Movies>> _future;

  Future<List<Movies>> fetchMovies() async {
    String jsonString = '''
    [{
"overview" : "with underground \\"fight clubs\\" forming in every town, until an eccentric gets in the way and ignites an out-of-control spiral toward oblivion",
"title" : "Fight Club"
},
{
"overview" : "test overview",
"title" : "test title"
}
]
    ''';

    var response = http.Response(jsonString, 200);

    if (response.statusCode == 200) {
      return moviesFromJson(jsonString);
    } else {
      print(response.statusCode);
    }
  }

  @override
  void initState() {
    _future = fetchMovies();
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text(widget.title),
        ),
        body: FutureBuilder(
            future: _future,
            builder: (context, AsyncSnapshot<List<Movies>> snapshot) {
              switch (snapshot.connectionState) {
                case ConnectionState.none:
                  return Text('none');
                case ConnectionState.waiting:
                  return Center(child: CircularProgressIndicator());
                case ConnectionState.active:
                  return Text('');
                case ConnectionState.done:
                  if (snapshot.hasError) {
                    return Text(
                      '${snapshot.error}',
                      style: TextStyle(color: Colors.red),
                    );
                  } else {
                    return ListView.builder(
                        itemCount: snapshot.data.length,
                        itemBuilder: (context, index) {
                          return Card(
                              elevation: 6.0,
                              child: Padding(
                                padding: const EdgeInsets.only(
                                    top: 6.0,
                                    bottom: 6.0,
                                    left: 8.0,
                                    right: 8.0),
                                child: Row(
                                  crossAxisAlignment: CrossAxisAlignment.start,
                                  children: <Widget>[
                                    Text(snapshot.data[index].title),
                                    Spacer(),
                                    Expanded(
                                      child: Text(
                                        snapshot.data[index].overview,
                                      ),
                                    ),
                                  ],
                                ),
                              ));
                        });
                  }
              }
            }));
  }
}

Answer 3

只需查看他的回答

[
    {
       "overview":"A ticking-time-bomb insomniac and a slippery soap salesman channel primal male aggression into a shocking new form of therapy. Their concept catches on, with underground \"fight clubs\" forming in every town, until an eccentric gets in the way and ignites an out-of-control spiral toward oblivion.",
       "title":"Fight Club"
    },
    {
       "overview":"A ticking-time-bomb insomniac and a slippery soap salesman channel primal male aggression into a shocking new form of therapy. Their concept catches on, with underground fight clubs forming in every town, until an eccentric gets in the way and ignites an out-of-control spiral toward oblivion.",
       "title":"second Club"
    }
 ]

型号

// To parse this JSON data, do
//
//     final movies = moviesFromJson(jsonString);

import 'dart:convert';

List<Movies> moviesFromJson(String str) => List<Movies>.from(json.decode(str).map((x) => Movies.fromJson(x)));

String moviesToJson(List<Movies> data) => json.encode(List<dynamic>.from(data.map((x) => x.toJson())));

class Movies {
    Movies({
        this.overview,
        this.title,
    });

    String overview;
    String title;

    factory Movies.fromJson(Map<String, dynamic> json) => Movies(
        overview: json["overview"],
        title: json["title"],
    );

    Map<String, dynamic> toJson() => {
        "overview": overview,
        "title": title,
    };
}

用户界面页面：

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:json_parsing_example/models.dart';

// To parse this JSON data, do
//
//     final user = userFromJson(jsonString);

void main() => runApp(new MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Flutter Demo',
      theme: new ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: new MyHomePage(title: 'Users'),
    );
  }
}

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

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  bool _isLoading = false;
  List<Movies> dataList = List();
  Future<String> loadFromAssets() async {
    return await rootBundle.loadString('json/parse.json');
  }

  @override
  void initState() {
    super.initState();
    getData();
  }

  getData() async {
    setState(() {
      _isLoading = true;
    });
    String jsonString = await loadFromAssets();
    final movies = moviesFromJson(jsonString);

    dataList = movies;

    setState(() {
      _isLoading = false;
    });
  }
    // In your case you just check out this code check out the model class
  /* Future <List<Movies>> fetchMovies () async {
    var response = await http.get(url);
    return moviesFromJson(response.body);

  } */

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text(widget.title),
      ),
      body: _isLoading
          ? Center(
              child: CircularProgressIndicator(),
            )
          : Container(
              child: ListView.builder(
                  itemCount: dataList.length,
                  shrinkWrap: true,
                  itemBuilder: (context, i) {
                    return Card(
                        child: Padding(
                      padding: const EdgeInsets.all(8.0),
                      child: Text(dataList[i].overview),
                    ));
                  }),
            ),
    );
  }
}

值得一提的是，概述的值带有双引号，这就是为什么可能存在一些解析问题的原因，只需检查代码并让我知道它是否有效。