Unhandled Exception: type 'Null' is not a subtype of type 'Map<String, dynamic>' in type cast

Question

import 'dart:convert';

import 'package:flutter/foundation.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];
  }

The errored block( when I do if check to null, vscode says The operand can't be null, so the condition is always false. also, I get an error saying Unhandled Exception: type 'Null' is not a subtype of type 'Map<String, dynamic>' in typecast.

  Future<void> fetchAndSetOrders() async {
    final url =
        Uri.https('shopapp-63-default-rtdb.firebaseio.com', '/orders.json');

    final response = await http.get(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;
    notifyListeners();
  }

Suraj Rao · Accepted Answer · 2022-05-08 15:33:22Z

2

try this method instead.

{
    final response = await http.get(url);
    final _data = json.decode(response.body);
    if (_data != null) {
        final extractedData = _data as Map<String, dynamic>;
    }

edited May 8, 2022 at 15:33

Suraj Rao

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answered May 8, 2022 at 15:24

JB Jason

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Comments

user18520267 · Accepted Answer · 2022-05-14 11:35:57Z

0

I think you are using Flutter 2.0+ which has nullsafety. Thus you can not check for a null to a variable which you do not define nullable explicitly.

Try defining

    final response = await http.get(url);
    final extractedData = json.de...

as

    final response? = await http.get(url);
    final extractedData? = json....

to slove The operand can't be null, so the condition is always false Then you can check null using ?? operator or with the if condition you are already using.

I don't know why null is not a subtype of type Map<String, dynamic> is occurring. Because your http.get(url) should not return null by any means.

edited May 14, 2022 at 11:35

user18520267

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answered Nov 2, 2021 at 9:36

Kaustuv Prajapati

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3 Comments

Narayan Poudel Over a year ago

when I add those question marks it shows a red line underneath wherever I use 'response' and 'extractedData' and it says The final variable 'response' can't be read because it is potentially unassigned at this point. Ensure that it is assigned on necessary execution

Kaustuv Prajapati Over a year ago

If you are now sure that your response is not NULL. then try accessing that variable using '!' at the end. Example. response!

Narayan Poudel Over a year ago

The '!' will have no effect because the receiver can't be null. Try removing the '!' operator. the error i got

Digital Psolite · Accepted Answer · 2022-11-17 05:21:48Z

0

it is caused by nullsafety

try defining

final extractedData = json.decode(response.body) as Map<String, dynamic>

as

final extractedData = json.decode(response.body) as Map<String, dynamic>?

answered Nov 17, 2022 at 5:21

Digital Psolite

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