问题：
类型列表不是类型转换中映射类型的子类型
壤驷涛
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，
{
"data": {
"quiz": {
"stats": {
"played": 6691,
"totalPlayers": "29553"
},
"publishedVersion": "5a13431202b92110003fdb92",
"_id": "5a133e2302b92110003fd8ef",
"createdBy": {
"local": {
"username": "jshutt"
},
"occupation": "teacher_school"
}, //createdBy
"info": {
"name": "Proportional Relationships",
"image": "https://quizizz.com/media/resource/gs/quizizz-media/quizzes/L2FwcGhvc3RpbmdfcHJvZC9ibG9icy9BRW5CMlVyNUFUSlN0VXhVSzcxY1hHZGN4UmJYVEdiWHRpeXBCcmVvQXhwT0JhckZwdnhBdkw4cHFqYjNVNktJSnlwSEdtUlJubV9Nc2Qxck51Z2Z5ampNSzJWb09Qek1tU0Joc0NaSUZtdGNyYzlQN1ZUQWREQS5EOUxuUGh3MUxaZzk0MUYz",
"subjects": [
"Mathematics"
],
"topics": [
"Pre-algebra"
],
"subtopics": [
"Proportional relationships",
"Constant of Proportionality",
"proportional graphs",
"proportion equations"
],
"questions": [
{
"structure": {
"kind": "MCQ",
"query": {
"media": [
{
"url": "https://quizizz.com/media/resource/gs/quizizz-media/questions/L2FwcGhvc3RpbmdfcHJvZC9ibG9icy9BRW5CMlVwajVWZnl0S2RBRXpIazROejFaSTl0dkU3Rmt6cjhtcTRvTGVxeFJzeHVLQzlZa3hzYjNZdkpNa3N1TTItaE5UNmVHUUZVdl9ZdTR6YnNaTk5hV0luZWhZQm9sUS5pOTBwLU1YLUtMRXR5YlBZ"
}
], //media
"text": "Write an equation for this relationship.",
}, //query
"options": [
{
"text": "y=1/5x"
},
{
"text": "y=1/2x"
},
{
"text": "y=2x"
},
{
"text": "y=5x"
}
], //options
"answer": 3
}
}
]
}
}
这是包含序列化类的代码，
import 'package:json_annotation/json_annotation.dart';
import 'questions_data/questions_quiz.dart';
part 'questions.g.dart';
@JsonSerializable(explicitToJson: true)
class CoreData {
QuestionData data;
CoreData({this.data});
factory CoreData.fromJson(Map<String, dynamic> json) => _$CoreDataFromJson(json);
Map<String, dynamic> toJson() => _$CoreDataToJson(this);
}
@JsonSerializable(explicitToJson: true)
class QuestionData {
Quiz quiz;
QuestionData({this.quiz});
factory QuestionData.fromJson(Map<String, dynamic> json) => _$QuestionDataFromJson(json);
Map<String, dynamic> toJson() => _$QuestionDataToJson(this);
}
@JsonSerializable(explicitToJson: true)
class QuestionsList {
List<Questions> questions;
QuestionsList({this.questions});
factory QuestionsList.fromJson(Map<String, dynamic> json) => _$QuestionsListFromJson(json);
Map<String, dynamic> toJson() => _$QuestionsListToJson(this);
}
@JsonSerializable(explicitToJson: true)
class Questions {
Structure structure;
Questions({this.structure});
factory Questions.fromJson(Map<String, dynamic> json) => _$QuestionsFromJson(json);
Map<String, dynamic> toJson() => _$QuestionsToJson(this);
}
@JsonSerializable(explicitToJson: true)
class Structure {
String kind;
Query query;
Options options;
int answer;
Structure({this.kind, this.query, this.options, this.answer});
factory Structure.fromJson(Map<String, dynamic> json) => _$StructureFromJson(json);
Map<String, dynamic> toJson() => _$StructureToJson(this);
}
@JsonSerializable(explicitToJson: true)
class Quiz {
String publishedVersion;
@JsonKey(name: '_id')
String id;
Stats stats;
CreatedBy createdBy;
Info info;
Quiz({this.publishedVersion, this.id, this.stats, this.createdBy, this.info});
factory Quiz.fromJson(Map<String, dynamic> json) => _$QuizFromJson(json);
Map<String, dynamic> toJson() => _$QuizToJson(this);
}
@JsonSerializable(explicitToJson: true)
class CreatedBy {
Local local;
String occupation;
CreatedBy({this.local, this.occupation});
factory CreatedBy.fromJson(Map<String, dynamic> json) => _$CreatedByFromJson(json);
Map<String, dynamic> toJson() => _$CreatedByToJson(this);
}
@JsonSerializable(explicitToJson: true)
class Local {
String username;
Local({this.username});
factory Local.fromJson(Map<String, dynamic> json) => _$LocalFromJson(json);
Map<String, dynamic> toJson() => _$LocalToJson(this);
}
@JsonSerializable(explicitToJson: true)
class Stats {
int played;
int totalPlayers;
Stats({this.played, this.totalPlayers});
factory Stats.fromJson(Map<String, dynamic> json) => _$StatsFromJson(json);
Map<String, dynamic> toJson() => _$StatsToJson(this);
}
@JsonSerializable(explicitToJson: true)
class Info {
String name;
String image;
List<String> subjects, topics, subtopics;
Questions questions;
Info({
this.name,
this.image,
this.subjects,
this.topics,
this.subtopics,
this.questions});
factory Info.fromJson(Map<String, dynamic> json) => _$InfoFromJson(json);
Map<String, dynamic> toJson() => _$InfoToJson(this);
}
@JsonSerializable(explicitToJson: true)
class Query {
String text;
List<Images> media;
Query({this.text, this.media});
factory Query.fromJson(Map<String, dynamic> json) => _$QueryFromJson(json);
Map<String, dynamic> toJson() => _$QueryToJson(this);
}
@JsonSerializable(explicitToJson: true)
class Images {
String url;
Images({this.url});
factory Images.fromJson(Map<String, dynamic> json) => _$ImagesFromJson(json);
Map<String, dynamic> toJson() => _$ImagesToJson(this);
}
@JsonSerializable(explicitToJson: true)
class Options {
List<QuestionText> options;
Options ({this.options});
factory Options.fromJson(Map<String, dynamic> json) => _$OptionsFromJson(json);
Map<String, dynamic> toJson() => _$OptionsToJson(this);
}
@JsonSerializable(explicitToJson: true)
class QuestionText {
String text;
QuestionText({this.text});
factory QuestionText.fromJson(Map<String, dynamic> json) => _$QuestionTextFromJson(json);
Map<String, dynamic> toJson() => _$QuestionTextToJson(this);
}
获取json文件并将其转换为dart的未来提供者，
import 'dart:convert' as convert;
import 'package:http/http.dart' as http;
import 'package:quizizz_cheat/models/questions.dart';
class QuestionsService {
Future<CoreData> fetchQuestion() async {
final response = await http.get(url);
var jsonResponse = convert.jsonDecode(response.body);
CoreData parsedQuestions = CoreData.fromJson(jsonResponse);
return parsedQuestions;
}
}
这是基因编码，
part of 'questions.dart';
// **************************************************************************
// JsonSerializableGenerator
// **************************************************************************
CoreData _$CoreDataFromJson(Map<String, dynamic> json) {
return CoreData(
data: json['data'] == null
? null
: QuestionData.fromJson(json['data'] as Map<String, dynamic>),
);
}
Map<String, dynamic> _$CoreDataToJson(CoreData instance) => <String, dynamic>{
'data': instance.data?.toJson(),
};
QuestionData _$QuestionDataFromJson(Map<String, dynamic> json) {
return QuestionData(
quiz: json['quiz'] == null
? null
: Quiz.fromJson(json['quiz'] as Map<String, dynamic>),
);
}
Map<String, dynamic> _$QuestionDataToJson(QuestionData instance) =>
<String, dynamic>{
'quiz': instance.quiz?.toJson(),
};
QuestionsList _$QuestionsListFromJson(Map<String, dynamic> json) {
return QuestionsList(
questions: (json['questions'] as List)
?.map((e) =>
e == null ? null : Questions.fromJson(e as Map<String, dynamic>))
?.toList(),
);
}
Map<String, dynamic> _$QuestionsListToJson(QuestionsList instance) =>
<String, dynamic>{
'questions': instance.questions?.map((e) => e?.toJson())?.toList(),
};
Questions _$QuestionsFromJson(Map<String, dynamic> json) {
return Questions(
structure: json['structure'] == null
? null
: Structure.fromJson(json['structure'] as Map<String, dynamic>),
);
}
Map<String, dynamic> _$QuestionsToJson(Questions instance) => <String, dynamic>{
'structure': instance.structure?.toJson(),
};
Structure _$StructureFromJson(Map<String, dynamic> json) {
return Structure(
kind: json['kind'] as String,
query: json['query'] == null
? null
: Query.fromJson(json['query'] as Map<String, dynamic>),
options: json['options'] == null
? null
: Options.fromJson(json['options'] as Map<String, dynamic>),
answer: json['answer'] as int,
);
}
Map<String, dynamic> _$StructureToJson(Structure instance) => <String, dynamic>{
'kind': instance.kind,
'query': instance.query?.toJson(),
'options': instance.options?.toJson(),
'answer': instance.answer,
};
Quiz _$QuizFromJson(Map<String, dynamic> json) {
return Quiz(
publishedVersion: json['publishedVersion'] as String,
id: json['_id'] as String,
stats: json['stats'] == null
? null
: Stats.fromJson(json['stats'] as Map<String, dynamic>),
createdBy: json['createdBy'] == null
? null
: CreatedBy.fromJson(json['createdBy'] as Map<String, dynamic>),
info: json['info'] == null
? null
: Info.fromJson(json['info'] as Map<String, dynamic>),
);
}
Map<String, dynamic> _$QuizToJson(Quiz instance) => <String, dynamic>{
'publishedVersion': instance.publishedVersion,
'_id': instance.id,
'stats': instance.stats?.toJson(),
'createdBy': instance.createdBy?.toJson(),
'info': instance.info?.toJson(),
};
CreatedBy _$CreatedByFromJson(Map<String, dynamic> json) {
return CreatedBy(
local: json['local'] == null
? null
: Local.fromJson(json['local'] as Map<String, dynamic>),
occupation: json['occupation'] as String,
);
}
Map<String, dynamic> _$CreatedByToJson(CreatedBy instance) => <String, dynamic>{
'local': instance.local?.toJson(),
'occupation': instance.occupation,
};
Local _$LocalFromJson(Map<String, dynamic> json) {
return Local(
username: json['username'] as String,
);
}
Map<String, dynamic> _$LocalToJson(Local instance) => <String, dynamic>{
'username': instance.username,
};
Stats _$StatsFromJson(Map<String, dynamic> json) {
return Stats(
played: json['played'] as int,
totalPlayers: json['totalPlayers'] as int,
);
}
Map<String, dynamic> _$StatsToJson(Stats instance) => <String, dynamic>{
'played': instance.played,
'totalPlayers': instance.totalPlayers,
};
Info _$InfoFromJson(Map<String, dynamic> json) {
return Info(
name: json['name'] as String,
image: json['image'] as String,
subjects: (json['subjects'] as List)?.map((e) => e as String)?.toList(),
topics: (json['topics'] as List)?.map((e) => e as String)?.toList(),
subtopics: (json['subtopics'] as List)?.map((e) => e as String)?.toList(),
questions: json['questions'] == null
? null
: Questions.fromJson(json['questions'] as Map<String, dynamic>),
);
}
Map<String, dynamic> _$InfoToJson(Info instance) => <String, dynamic>{
'name': instance.name,
'image': instance.image,
'subjects': instance.subjects,
'topics': instance.topics,
'subtopics': instance.subtopics,
'questions': instance.questions?.toJson(),
};
Query _$QueryFromJson(Map<String, dynamic> json) {
return Query(
text: json['text'] as String,
media: (json['media'] as List)
?.map((e) =>
e == null ? null : Images.fromJson(e as Map<String, dynamic>))
?.toList(),
);
}
Map<String, dynamic> _$QueryToJson(Query instance) => <String, dynamic>{
'text': instance.text,
'media': instance.media?.map((e) => e?.toJson())?.toList(),
};
Images _$ImagesFromJson(Map<String, dynamic> json) {
return Images(
url: json['url'] as String,
);
}
Map<String, dynamic> _$ImagesToJson(Images instance) => <String, dynamic>{
'url': instance.url,
};
Options _$OptionsFromJson(Map<String, dynamic> json) {
return Options(
options: (json['options'] as List)
?.map((e) =>
e == null ? null : QuestionText.fromJson(e as Map<String, dynamic>))
?.toList(),
);
}
Map<String, dynamic> _$OptionsToJson(Options instance) => <String, dynamic>{
'options': instance.options?.map((e) => e?.toJson())?.toList(),
};
QuestionText _$QuestionTextFromJson(Map<String, dynamic> json) {
return QuestionText(
text: json['text'] as String,
);
}
Map<String, dynamic> _$QuestionTextToJson(QuestionText instance) =>
<String, dynamic>{
'text': instance.text,
};
这是转换后的json文件显示的代码
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import 'package:quiz/screens/home.dart';
import 'package:quiz/services/questions_service.dart';
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
final QuestionsService questionsService = QuestionsService();
@override
Widget build(BuildContext context) {
return FutureProvider(
create: (context) async => questionsService.fetchQuestion(),
catchError: (context, error) {
print(error.toString());
},
child: MaterialApp(
title: 'Quizizz cheat',
home: HomePage(),
),
);
}
}
class HomePage extends StatelessWidget {
@override
Widget build(BuildContext context) {
var question = Provider.of<CoreData>(context);
return Scaffold(
appBar: AppBar(
title: Text('Quizizz Cheat'),
),
body: question == null
? Center(child: CircularProgressIndicator())
: Center(
child: Text(question.data.quiz.info.questions.structure.kind),
),
);
}
}
当我试着运行这个项目时，我遇到了这个错误
i/flutter（23347）： type'List'不是type'Map的子类型
我相信问题来自这段代码，它试图转换包含映射列表的json和包含json序列化方法的代码
@JsonSerializable(explicitToJson: true)
class QuestionsList {
List<Questions> questions;
QuestionsList({this.questions});
factory QuestionsList.fromJson(Map<String, dynamic> json) => _$QuestionsListFromJson(json);
Map<String, dynamic> toJson() => _$QuestionsListToJson(this);
}
共有1个答案
喻珂
我已经解决了这个问题，似乎在编写代码时需要更加小心。答案很简单，我需要改变这个类型。。。
@JsonSerializable(explicitToJson: true)
class Info {
String name;
String image;
List<String> subjects, topics, subtopics;
Questions questions;
Info({
this.name,
this.image,
this.subjects,
this.topics,
this.subtopics,
this.questions});
factory Info.fromJson(Map<String, dynamic> json) => _$InfoFromJson(json);
Map<String, dynamic> toJson() => _$InfoToJson(this);
}
对此。。。
@JsonSerializable(explicitToJson: true)
class Info {
String name;
String image;
List<String> subjects, topics, subtopics;
List<Questions> questions;
Info({
this.name,
this.image,
this.subjects,
this.topics,
this.subtopics,
this.questions});
factory Info.fromJson(Map<String, dynamic> json) => _$InfoFromJson(json);
Map<String, dynamic> toJson() => _$InfoToJson(this);
}
而从这个...
@JsonSerializable(explicitToJson: true)
class Structure {
String kind;
Query query;
Options options;
int answer;
Structure({this.kind, this.query, this.options, this.answer});
factory Structure.fromJson(Map<String, dynamic> json) => _$StructureFromJson(json);
Map<String, dynamic> toJson() => _$StructureToJson(this);
}
对此。。。
@JsonSerializable(explicitToJson: true)
class Structure {
String kind;
Query query;
List<QuestionText> options;
int answer;
Structure({this.kind, this.query, this.options, this.answer});
factory Structure.fromJson(Map<String, dynamic> json) => _$StructureFromJson(json);
Map<String, dynamic> toJson() => _$StructureToJson(this);
}
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