我在此代码块中收到一个错误，显示"_TypeError（type 'String' is not a subtype of type 'int' of 'index'）"。当我转到应用的订单页面时发生错误。它在amount:和datetime:上显示错误。当我在购物车结账时，它会将购物车发送到数据库，但是，当我转到订单页面时，错误发生。

extractedData.forEach((orderId, orderData) {
      loadedOrders.add(
        OrderItem(
          id: orderId,
          amount: orderData['amount'],
          dateTime: DateTime.parse(orderData['dateTime']),
          products: (orderData['products'] as List<dynamic>)
              .map(
                (item) => CartItem(
                  id: item['id'],
                  title: item['title'],
                  quantity: item['quantity'],
                  price: item['price'],
                ),
              )
              .toList(),

这是我的数据库：

shopapp-6740d-default-rtdb:
       orders: -MpxLeVE1f5xosVHiYdM
                 amount: 59.99
                 dateTime: "2021-12-02T17:53:52.689091"
                 products: 0
                      id: "2021-12-02 17:53:50.251572"
                      price: 59.99
                      quantity: 1
                      title: "Trousers"

这是我的全部代码。

import 'dart:convert';

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

import './cart.dart';

class OrderItem {
  final String id;
  final double amount;
  final List<CartItem> products;
  final DateTime dateTime;

  OrderItem({
    required this.id,
    required this.amount,
    required this.products,
    required this.dateTime,
  });
}

class Orders with ChangeNotifier {
  List<OrderItem> _orders = [];

  List<OrderItem> get orders {
    return [..._orders];
  }

  Future<void> fetchAndSetOrders() async {
    const url = 'https://shopapp-6740d-default-rtdb.firebaseio.com/orders.json';

    final response = await http.post(Uri.parse(url));
    final List<OrderItem> loadedOrders = [];
    final extractedData = json.decode(response.body) as Map<String, dynamic>;

    if(extractedData == null){
      return;
    }

    extractedData.forEach((orderId, orderData) {
      loadedOrders.add(
        OrderItem(
          id: orderId,
          amount: orderData['amount'],
          dateTime: DateTime.parse(orderData['dateTime']),
          products: (orderData['products'] as List<dynamic>)
              .map(
                (item) => CartItem(
                  id: item['id'],
                  title: item['title'],
                  quantity: item['quantity'],
                  price: item['price'],
                ),
              )
              .toList(),
        ),
      );
    });
    _orders = loadedOrders.reversed.toList();
    notifyListeners();
  }

  Future<void> addOrder(List<CartItem> cartProducts, double total) async {
    const url = 'https://shopapp-6740d-default-rtdb.firebaseio.com/orders.json';
    final timestamp = DateTime.now();
    final response = await http.post(
      Uri.parse(url),
      body: json.encode({
        'amount': total,
        'dateTime': DateTime.now().toIso8601String(),
        'products': cartProducts
            .map((cp) => {
                  'id': cp.id,
                  'title': cp.title,
                  'quantity': cp.quantity,
                  'price': cp.price,
                })
            .toList(),
      }),
    );

    _orders.insert(
      0,
      OrderItem(
        id: json.decode(response.body)['name'],
        amount: total,
        products: cartProducts,
        dateTime: DateTime.now(),
      ),
    );
    notifyListeners();
  }
}