Node.js 和 Dart：未处理的异常：类型“String”不是“index”的“int”类型的子类型

这是完整的错误：

E/flutter (10656): [错误:flutter/runtime/dart_vm_initializer(41)] 未处理的异常：类型“String”不是类型“int”的子类型 'index' E/flutter (10656): #0 _DashboardState.getTodoList dashboard.dart:69 E/颤动 (10656):

我该如何解决这个问题？

这是我的代码：

import 'dart:convert';
import 'package:flutter/material.dart';
import 'package:jwt_decoder/jwt_decoder.dart';
import 'package:velocity_x/velocity_x.dart';
import 'package:http/http.dart' as http;
import 'config.dart';
import 'package:flutter_slidable/flutter_slidable.dart';

class Dashboard extends StatefulWidget {
  final token;
  const Dashboard({@required this.token, Key? key}) : super(key: key);

  @override
  State<Dashboard> createState() => _DashboardState();
}

class _DashboardState extends State<Dashboard> {
  late String userId;
  final TextEditingController _todoTitle = TextEditingController();
  final TextEditingController _todoDesc = TextEditingController();
  List? items = [];
  @override
  void initState() {
    super.initState();
    Map<String, dynamic> jwtDecodedToken = JwtDecoder.decode(widget.token);

    userId = jwtDecodedToken['_id'];
    getTodoList(userId);
  }

  void addTodo() async {
    if (_todoTitle.text.isNotEmpty && _todoDesc.text.isNotEmpty) {
      var regBody = {
        "userId": userId,
        "title": _todoTitle.text,
        "desc": _todoDesc.text
      };

      var response = await http.post(Uri.parse(addtodo),
          headers: {"Content-Type": "application/json"},
          body: jsonEncode(regBody));

var jsonResponse= await json.decode(json.encode(response.body));  
      // var jsonResponse = jsonDecode(response.body);

      print(jsonResponse['status']);

      if (jsonResponse['status']) {
        _todoDesc.clear();
        _todoTitle.clear();
        Navigator.pop(context);
        getTodoList(userId);
      } else {
        print("SomeThing Went Wrong");
      }
    }
  }

  void getTodoList(userId) async {
    var regBody = {"userId": userId};

    var response = await http.post(Uri.parse(getToDoList),
        headers: {"Content-Type": "application/json"},
        body: jsonEncode(regBody));

var jsonResponse= await json.decode(json.encode(response.body));  
    // var jsonResponse = jsonDecode(response.body);

    items = jsonResponse['success'];

    setState(() {});
  }

  void deleteItem(id) async {
    var regBody = {"id": id};

    var response = await http.post(Uri.parse(deleteTodo),
        headers: {"Content-Type": "application/json"},
        body: jsonEncode(regBody));

    var jsonResponse = jsonDecode(response.body);
    if (jsonResponse['status']) {
      getTodoList(userId);
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.lightBlueAccent,
      body: Column(
        crossAxisAlignment: CrossAxisAlignment.start,
        children: [
          Container(
            padding: const EdgeInsets.only(
                top: 60.0, left: 30.0, right: 30.0, bottom: 30.0),
            child: const Column(
              crossAxisAlignment: CrossAxisAlignment.start,
              children: [
                CircleAvatar(
                  backgroundColor: Colors.white,
                  radius: 30.0,
                  child: Icon(
                    Icons.list,
                    size: 30.0,
                  ),
                ),
                SizedBox(height: 10.0),
                Text(
                  'ToDo with NodeJS + Mongodb',
                  style: TextStyle(fontSize: 30.0, fontWeight: FontWeight.w700),
                ),
                SizedBox(height: 8.0),
                Text(
                  'Add your todo and get started!',
                  style: TextStyle(fontSize: 30.0, color: Colors.white),
                ),
              ],
            ),
          ),
          Expanded(
            child: Container(
              width: MediaQuery.of(context).size.width,
              decoration: const BoxDecoration(
                  color: Colors.white,
                  borderRadius: BorderRadius.only(
                      topLeft: Radius.circular(20),
                      topRight: Radius.circular(20))),
              child: Padding(
                padding: const EdgeInsets.all(8.0),
                child: items == null
                    ? null
                    : ListView.builder(
                        itemCount: items!.length,
                        itemBuilder: (context, int index) {
                          return Slidable(
                            key: const ValueKey(0),
                            endActionPane: ActionPane(
                              motion: const ScrollMotion(),
                              dismissible: DismissiblePane(onDismissed: () {}),
                              children: [
                                SlidableAction(
                                  backgroundColor: const Color(0xFFFE4A49),
                                  foregroundColor: Colors.black,
                                  icon: Icons.delete,
                                  label: 'Delete',
                                  onPressed: (BuildContext context) {
                                    print('${items![index]['_id']}');
                                    deleteItem('${items![index]['_id']}');
                                  },
                                ),
                              ],
                            ),
                            child: Card(
                              borderOnForeground: false,
                              child: ListTile(
                                leading: const Icon(Icons.task),
                                title: Text('${items![index]['title']}'),
                                subtitle: Text('${items![index]['desc']}'),
                                trailing: const Icon(Icons.arrow_back),
                              ),
                            ),
                          );
                        }),
              ),
            ),
          )
        ],
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () => _displayTextInputDialog(context),
        tooltip: 'Add-ToDo',
        child: Icon(Icons.add),
      ),
    );
  }

  Future<void> _displayTextInputDialog(BuildContext context) async {
    return showDialog(
        context: context,
        builder: (context) {
          return AlertDialog(
              title: const Text('Add To-Do'),
              content: Column(
                mainAxisSize: MainAxisSize.min,
                children: [
                  TextField(
                    controller: _todoTitle,
                    keyboardType: TextInputType.text,
                    decoration: const InputDecoration(
                        filled: true,
                        fillColor: Colors.white,
                        hintText: "Title",
                        border: OutlineInputBorder(
                            borderRadius:
                                BorderRadius.all(Radius.circular(10.0)))),
                  ).p4().px8(),
                  TextField(
                    controller: _todoDesc,
                    keyboardType: TextInputType.text,
                    decoration: const InputDecoration(
                        filled: true,
                        fillColor: Colors.white,
                        hintText: "Description",
                        border: OutlineInputBorder(
                            borderRadius:
                                BorderRadius.all(Radius.circular(10.0)))),
                  ).p4().px8(),
                  ElevatedButton(
                      onPressed: () {
                        addTodo();
                      },
                      child: const Text("Add"))
                ],
              ));
        });
  }
}

config.dart

const url = 'http://x:3000/';
const registration = "${url}registration";
const login = '${url}login';
const addtodo = '${url}storeTodo';
const getToDoList =  url + 'getUserTodoList';
const deleteTodo = '${url}deleteTodo';

todo.router.js

const router = require('express').Router();
const TodoController = require('../controller/todo.controller');

router.post('/storeTodo', TodoController.createTodo); 

router.get('/getUserTodoList', TodoController.getUserTodo);

module.exports = router;

我试过这个：

List? items = [];

List? items;

感谢您提供的任何帮助