错误：清单 不是Map类型的子类型

  • Z时代
  • 2024-01-10
  • 分类：问答

我目前正在构建一个应用程序，以通过api读取数据，并且试图从JSON Placeholder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"]
    );
  }
}

这是将json读取到小部件中的main.dart：

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"
}
}

我当前遇到的错误是：

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

我该如何纠正此错误？

回答：

API返回JSON数组而不是json对象，因此列表不是Map。

即用户json是Json Array的第一个元素。

因此，要获取第一个元素，请使用第一个索引。内部获取信息更新

return Users.fromJson(jsonresponse[0]);

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