类型列表动态不是类型映射字符串动态的子类型

Question

这是显示类型列表动态不是类型映射字符串动态的子类型“现在当我运行模拟器时，显示”类型列表动态不是类型映射字符串动态的子类型“在我的模拟器上，我如何修复它？

现在我想创建关于查找api id的程序，从我的模拟器中使用文本字段和按钮，当我把一些数字和单击按钮时，会显示该ID的数据或标题，但我只是初学者，所以如果有人认为我的代码是正确的或不正确的或者你有推荐请告诉我
My JSON

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

Future<Album> fetchAlbum() async {
  final response =
  await http.get(Uri.parse('http://192.168.176.131:3000/api/courses/'));

  if (response.statusCode == 200) {
    // If the server did return a 200 OK response,
    // then parse the JSON.
    return Album.fromJson(jsonDecode(response.body));

  } else {
    // If the server did not return a 200 OK response,
    // then throw an exception1
    throw Exception('Failed to load album');
  }
}

class Album {
  final int userId;
  final int id;
  final String title;

  Album({
    required this.userId,
    required this.id,
    required this.title,
  });

  factory Album.fromJson(Map<String, dynamic> json) {
    return Album(
      userId: json['userId'],
      id: json['id'],
      title: json['title'],
    );
  }
}

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

class MyApp extends StatefulWidget {
  MyApp({Key? key}) : super(key: key);


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

class _MyAppState extends State<MyApp> {
  late Future<Album> futureAlbum;

  @override
  void initState() {
    super.initState();
    futureAlbum = fetchAlbum();
  }

  Widget build(BuildContext context) {
    TextEditingController searchController = new TextEditingController();
    return MaterialApp(
      title: 'Fetch Data Example',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: Scaffold(
          appBar: AppBar(
            title: Text('Fetch Data Example'),
          ),

          body: Column(children: [
            Container(
                child: Row(children: [
                  Expanded(
                      flex: 2,
                      child: TextField(
                          controller: searchController
                      )
                  ),
                  Expanded(
                      flex: 1,
                      child: FlatButton(
                        onPressed: () {
                          print(
                              "this is the text to search for => ${searchController
                                  .text}");
                        },
                        child: Text("Search"),
                      )
                  )
                ],)
            ),
            Center(
              child: FutureBuilder<Album>(
                future: futureAlbum,
                builder: (context, snapshot) {
                  if (snapshot.hasData) {
                    return Text(snapshot.data!.title);
                  } else if (snapshot.hasError) {
                    return Text("${snapshot.error}");
                  }
                  // By default, show a loading spinner.
                  return CircularProgressIndicator();
                },
              ),
            ),
          ],)

      ),
    );
  }
}

JSON代码

const Joi = require('joi');
const express = require('express');
const app = express();

app.use(express.json());

const courses = [
    { userId:1, id:1, title:'course 1'},
    { userId:2, id:2, title:'course 2'},
    { userId:3, id:3, title:'course 3'},
]; 

app.get('/', (req,res)  => {
    res.send('Hello world');

});

app.get('/api/courses',(req, res) => {
    res.send(courses);
});

app.post('/api/courses', (req, res) => {   
    const { error }  = validateCourse(req.body);
    if (error)return res.status(400).send(error.details[0].message);


    const course = {
        id: courses.length +1,
        name: req.body.name
    };
    courses.push(course);
    res.send(course);
});

app.put('/api/courses/:id', (req, res) => {
    const course = courses.find(c => c.id === parseInt(req.params.id));
    if (!course) return res.status(404).send('The course with the given ID was not found.');

    const {error} = validateCourse(req.body); //result.eror
    if (error) return res.status(400).send(error.details[0].message);
        
    
    //Update course
    course.name = req.body.name;
    res.send(course);
    //Return the updated course

});



app.delete('/api/courses/:id', (req, res) => {
    const course = courses.find(c => c.id === parseInt(req.params.id));
    if (!course) return res.status(404).send('The course with the given ID was not found.');

    const index = courses.indexOf(course);
    courses.splice(index, 1);
    res.send(course);
});
function validateCourse(course){
    const schema = {
        name: Joi.string().min(3).required()
    };

    return Joi.validate(course, schema);
}

应用程序。获取（'/api/courses/:id'，（请求，资源）=

const port=进程。环境。港口| | 3000//应用程序。侦听（端口，（）=

Answer 1

您应该将jsonDecode返回的值强制转换为映射