未处理的异常：类型 'List<dynamic>' 不是类型 'Map<String, dynamic
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【中文标题】未处理的异常：类型 \'List<dynamic>\' 不是类型 \'Map<String, dynamic【英文标题】：Unhandled Exception: type 'List<dynamic>' is not a subtype of type 'Map<String, dynamic未处理的异常：类型 'List<dynamic>' 不是类型 'Map<String, dynamic 【发布时间】：2020-11-05 13:15:32 【问题描述】：我正在解码响应正文并收到错误消息：
[ERROR:flutter/lib/ui/ui_dart_state.cc(157)] Unhandled Exception: type 'List<dynamic>' is not a subtype of type 'Map<String, dynamic>'
我正在尝试使用 API，同时遵循 Udemy 上的颤振教程。该教程说使用 https://javiercbk.github.io/json_to_dart/ 将 JSON 转换为 Dart。我从https://www.openbrewerydb.org/ 获取 JSON 并将其转换为 Dart，但我遇到的问题是当我尝试解码 API 时出现错误 Unhandled Exception: type 'List' is not a subtype of type 'Map
作为 Flutter/Dart 的新手，我不确定如何解决此类错误。我的代码发布在下面以供参考。欢迎任何帮助！
BreweryModel.dart
class BreweryModel
int id;
String name;
String breweryType;
String street;
String city;
String state;
String postalCode;
String country;
String longitude;
String latitude;
String phone;
String websiteUrl;
String updatedAt;
BreweryModel(
this.id,
this.name,
this.breweryType,
this.street,
this.city,
this.state,
this.postalCode,
this.country,
this.longitude,
this.latitude,
this.phone,
this.websiteUrl,
this.updatedAt);
factory BreweryModel.fromJson(Map<String, dynamic> json)
return BreweryModel(
id: json['id'],
name: json['name'],
breweryType: json['brewery_type'],
street: json['street'],
city: json['city'],
state: json['state'],
postalCode: json['postal_code'],
country: json['country'],
phone: json['phone']);
Map<String, dynamic> toJson()
final Map<String, dynamic> data = new Map<String, dynamic>();
data['id'] = this.id;
data['name'] = this.name;
data['brewery_type'] = this.breweryType;
data['street'] = this.street;
data['city'] = this.city;
data['state'] = this.state;
data['postal_code'] = this.postalCode;
data['country'] = this.country;
data['longitude'] = this.longitude;
data['latitude'] = this.latitude;
data['phone'] = this.phone;
data['website_url'] = this.websiteUrl;
data['updated_at'] = this.updatedAt;
return data;
Network.dart
import 'package:brewery_app/model/BreweryModel.dart';
import 'package:http/http.dart';
import 'dart:convert';
class Network
Future<BreweryModel> getBreweryModel(String cityName) async
var URL = 'https://api.openbrewerydb.org/breweries?by_city=$cityName';
final response = await get(Uri.encodeFull(URL));
print('URL $Uri.encodeFull(URL)');
if (response.statusCode == 200)
print(response.body);
return BreweryModel.fromJson(json.decode(response.body));
else
throw Exception('Error getting brewery');
Main.dart
import 'package:brewery_app/model/BreweryModel.dart';
import 'package:brewery_app/network/network.dart';
import 'package:flutter/material.dart';
void main()
runApp(MyApp());
class MyApp extends StatelessWidget
// This widget is the root of your application.
@override
Widget build(BuildContext context)
return MaterialApp(
home: Brewery(),
);
class Brewery extends StatefulWidget
@override
_BreweryState createState() => _BreweryState();
class _BreweryState extends State<Brewery>
Future<BreweryModel> breweryObject;
String cityName = 'Austin';
@override
void initState()
// TODO: implement initState
super.initState();
breweryObject = Network().getBreweryModel(cityName: cityName);
breweryObject.then((brewery)
print(brewery.city);
);
@override
Widget build(BuildContext context)
return Container();
这是发布到控制台的所有内容
I/flutter (25205): URL https://api.openbrewerydb.org/breweries?by_city=Austin
I/flutter (25205): ["id":6780,"name":"Jester King Brewery","brewery_type":"micro","street":"13187 Fitzhugh Rd","city":"Austin","state":"Texas","postal_code":"78736-6510","country":"United States","longitude":"-98.0824692","latitude":"30.2547264","phone":"5125375100","website_url":"http://www.jesterkingbrewery.com","updated_at":"2018-08-24T16:21:26.875Z","tag_list":[],"id":6822,"name":"Oasis Texas Brewing Company","brewery_type":"micro","street":"6548 Comanche Trl Ste 301","city":"Austin","state":"Texas","postal_code":"78732-1210","country":"United States","longitude":"-98.151206","latitude":"30.043267","phone":"5122849407","website_url":"http://www.otxbc.com","updated_at":"2018-08-24T16:22:10.184Z","tag_list":[],"id":6631,"name":"Barking Armadillo Brewing","brewery_type":"planning","street":"","city":"Austin","state":"Texas","postal_code":"78723-3342","country":"United States","longitude":null,"latitude":null,"phone":"","website_url":"","updated_at":"2018-08-11T21:39:46.076Z","tag_list":[],"id":6632,"name":"Barrel Assem
E/flutter (25205): [ERROR:flutter/lib/ui/ui_dart_state.cc(157)] Unhandled Exception: type 'List<dynamic>' is not a subtype of type 'Map<String, dynamic>'
E/flutter (25205): #0 Network.getBreweryModel (package:brewery_app/network/network.dart:15:41)
E/flutter (25205): <asynchronous suspension>
E/flutter (25205): #1 _BreweryState.initState (package:brewery_app/main.dart:31:31)
E/flutter (25205): #2 StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:4640:58)
E/flutter (25205): #3 ComponentElement.mount (package:flutter/src/widgets/framework.dart:4476:5)
E/flutter (25205): #4 Element.inflateWidget (package:flutter/src/widgets/framework.dart:3446:14)
E/flutter (25205): #5 Element.updateChild (package:flutter/src/widgets/framework.dart:3214:18)
E/flutter (25205): #6 SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:5830:14)
E/flutter (25205): #7 Element.inflateWidget (package:flutter/src/widgets/framework.dart:3446:14)
E/flutter (25205): #8 Element.updateChild (package:flutter/src/widgets/framework.dart:3214:18)
E/flutter (25205): #9 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4527:16)
E/flutter (25205): #10 Element.rebuild (package:flutter/src/widgets/framework.dart:4218:5)
E/flutter (25205): #11 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:4481:5)
E/flutter (25205): #12 ComponentElement.mount (package:flutter/src/widgets/framework.dart:4476:5)
E/flutter (25205): #13 Element.inflateWidget (package:flutter/src/widgets/framework.dart:3446:14)
E/flutter (25205): #14 Element.updateChild (package:flutter/src/widgets/framework.dart:3214:18)
E/flutter (25205): #15 SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:5830:14)
E/flutter (25205): #16 Element.inflateWidget (package:flutter/src/widgets/framework.dart:3446:14)
E/flutter (25205): #17 Element.updateChild (package:flutter/src/widgets/framework.dart:3214:18)
E/flutter (25205): #18 SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:5830:14)
E/flutter (25205): #19 Element.inflateWidget (package:flutter/src/widgets/framework.dart:3446:14)
E/flutter (25205): #20 Element.updateChild (package:flutter/src/widgets/framework.dart:3214:18)
E/flutter (25205): #21 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4527:16)
E/flutter (25205): #22 StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4675:11)
E/flutter (25205): #23 Element.rebuild (package:flutter/src/widgets/framework.dart:4218:5)
E/flutter (25205): #24 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:4481:5)
E/flutter (25205): #25 StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:4666:11)
E/flutter (25205): #26 ComponentElement.mount (package:flutter/src/widgets/framework.dart:4476:5)
E/flutter (25205): #27 Element.inflateWidget (package:flutter/src/widgets/framework.dart:3446:14)
E/flutter (25205): #28 Element.updateChild (package:flutter/src/widgets/framework.dart:3214:18)
E/flutter (25205): #29 SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:5830:14)
E/flutter (25205): #30 Element.inflateWidget (package:flutter/src/widgets/framework.dart:3446:14)
E/flutter (25205): #31 Element.updateChild (package:flutter/src/widgets/framework.dart:3214:18)
E/flutter (25205): #32 SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:5830:14)
E/flutter (25205): #33 Element.inflateWidget (package:flutter/src/widgets/framework.dart:3446:14)
E/flutter (25205): #34 Element.updateChild (package:flutter/src/widgets/framework.dart:3214:18)
E/flutter (25205): #35 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4527:16)
E/flutter (25205): #36 StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4675:11)
E/flutter (25205): #37 Element.rebuild (package:flutter/src/widgets/framework.dart:4218:5)
E/flutter (25205): #38 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:4481:5)
E/flutter (25205): #39 StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:4666:11)
E/flutter (25205): #40 ComponentElement.mount (package:flutter/src/widgets/framework.dart:4476:5)
E/flutter (25205): #41 Element.inflateWidget (package:flutter/src/widgets/framework.dart:3446:14)
E/flutter (25205): #42 Element.updateChild (package:flutter/src/widgets/framework.dart:3214:18)
E/flutter (25205): #43 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4527:16)
E/flutter (25205): #44 Element.rebuild (package:flutter/src/widgets/framework.dart:4218:5)
E/flutter (25205): #45 ComponentElement._firstBuild (package:flutter
【问题讨论】：
你能澄清你的错误吗？您的标题表明与正文所说的不同。也请直接复制粘贴出错。 我编辑了帖子，希望能澄清我遇到的错误。 【参考方案1】：您可以在下面复制粘贴运行完整代码
第 1 步：将Future<List<BreweryModel>> 用于breweryObject;
Future<List<BreweryModel>> breweryObject;
第 2 步：将Future<List<BreweryModel>> 用于getBreweryModel
Future<List<BreweryModel>> getBreweryModel(String cityName) async
var URL = 'https://api.openbrewerydb.org/breweries?by_city=$cityName';
final response = await http.get(Uri.encodeFull(URL));
print('URL $Uri.encodeFull(URL)');
if (response.statusCode == 200)
print(response.body);
return breweryModelFromJson(response.body);
第 3 步：在 getBreweryModel() 中，您需要返回 breweryModelFromJson(response.body)，因为它是 List<BreweryModel>
工作演示
完整代码
import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
import 'dart:convert';
List<BreweryModel> breweryModelFromJson(String str) => List<BreweryModel>.from(
json.decode(str).map((x) => BreweryModel.fromJson(x)));
String breweryModelToJson(List<BreweryModel> data) =>
json.encode(List<dynamic>.from(data.map((x) => x.toJson())));
class BreweryModel
int id;
String name;
String breweryType;
String street;
String city;
String state;
String postalCode;
String country;
String longitude;
String latitude;
String phone;
String websiteUrl;
String updatedAt;
BreweryModel(
this.id,
this.name,
this.breweryType,
this.street,
this.city,
this.state,
this.postalCode,
this.country,
this.longitude,
this.latitude,
this.phone,
this.websiteUrl,
this.updatedAt);
factory BreweryModel.fromJson(Map<String, dynamic> json)
return BreweryModel(
id: json['id'],
name: json['name'],
breweryType: json['brewery_type'],
street: json['street'],
city: json['city'],
state: json['state'],
postalCode: json['postal_code'],
country: json['country'],
phone: json['phone']);
Map<String, dynamic> toJson()
final Map<String, dynamic> data = new Map<String, dynamic>();
data['id'] = this.id;
data['name'] = this.name;
data['brewery_type'] = this.breweryType;
data['street'] = this.street;
data['city'] = this.city;
data['state'] = this.state;
data['postal_code'] = this.postalCode;
data['country'] = this.country;
data['longitude'] = this.longitude;
data['latitude'] = this.latitude;
data['phone'] = this.phone;
data['website_url'] = this.websiteUrl;
data['updated_at'] = this.updatedAt;
return data;
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: Brewery(title: 'Flutter Demo Home Page'),
);
class Network
Future<List<BreweryModel>> getBreweryModel(String cityName) async
var URL = 'https://api.openbrewerydb.org/breweries?by_city=$cityName';
final response = await http.get(Uri.encodeFull(URL));
print('URL $Uri.encodeFull(URL)');
if (response.statusCode == 200)
print(response.body);
return breweryModelFromJson(response.body);
else
throw Exception('Error getting brewery');
class Brewery extends StatefulWidget
Brewery(Key key, this.title) : super(key: key);
final String title;
@override
_BreweryState createState() => _BreweryState();
class _BreweryState extends State<Brewery>
Future<List<BreweryModel>> breweryObject;
String cityName = 'Austin';
@override
void initState()
super.initState();
breweryObject = Network().getBreweryModel(cityName: cityName);
@override
Widget build(BuildContext context)
return Scaffold(
appBar: AppBar(
title: Text("Demo"),
),
body: FutureBuilder(
future: breweryObject,
builder: (context, AsyncSnapshot<List<BreweryModel>> snapshot)
switch (snapshot.connectionState)
case ConnectionState.none:
return Text('none');
case ConnectionState.waiting:
return Center(child: CircularProgressIndicator());
case ConnectionState.active:
return Text('');
case ConnectionState.done:
if (snapshot.hasError)
return Text(
'$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].name,
),
Spacer(),
Text(
snapshot.data[index].street,
),
],
),
));
);
));
【讨论】：
【参考方案2】：示例 JSON here 显示了一个示例输出，它将是您代码中 BreweryModels 的 List。因此，您应该尝试生成List 的BreweryModels。当您使用 JSON 到 dart 转换器时，您可能没有复制整个示例 JSON。以下是处理正确接收的List 的示例修复，但您实际需要的内容可能会因您的预期应用程序而异。
网络类：
返回List 的BreweryModels：
Future<List<BreweryModel>> getBreweryModel(String cityName) async
var URL = 'https://api.openbrewerydb.org/breweries?by_city=$cityName';
final response = await get(Uri.encodeFull(URL));
print('URL $Uri.encodeFull(URL)');
if (response.statusCode == 200)
print(response.body);
List<BreweryModel> toReturn = List()
List json = json.decode(response.body);
for(Map unparsed in json)
toReturn.add(BreweryModel.fromJson(unparsed);
return toReturn;
else
throw Exception('Error getting brewery');
或者如果您只希望收到的 JSON 中有一个啤酒厂：
Future<BreweryModel> getBreweryModel(String cityName) async
var URL = 'https://api.openbrewerydb.org/breweries?by_city=$cityName';
final response = await get(Uri.encodeFull(URL));
print('URL $Uri.encodeFull(URL)');
if (response.statusCode == 200)
print(response.body);
return BreweryModel.fromJson(json.decode(response.body)[0]);
else
throw Exception('Error getting brewery');
【讨论】：
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