Unable to access the data from the provider - flutter

Question

I wish to print the quantity of the items selected but am not able to do so. I am using providers to access data but it's showing some error. The same method worked when I applied it elsewhere but it doesn't seem to work here Please help.
Snippet for the type of data I receive:
{
"delivery_status": true,
"coupon_code": null,
"cart": [
{
"food_item_id": "2c7289c1-17fb-4f3a-90af-7a014e051c53",
"name": "Grape",
"price": 35.0,
"category": "Fresh Fruit Juice",
"available": true,
"veg": false,
"egg": false,
"restaurant": "9adafbd7-a9ba-4890-b707-c9d619c72f02",
"quantity": 1
},
{
"food_item_id": "be303557-90ce-4f9c-a30f-5a6d650977b6",
"name": "Mix Juice",
"price": 35.0,
"category": "Fresh Fruit Juice",
"available": true,
"veg": false,
"egg": false,
"restaurant": "9adafbd7-a9ba-4890-b707-c9d619c72f02",
"quantity": 2
},
{
"food_item_id": "13fb9de8-c774-4f6d-af66-74cc6dedbf14",
"name": "Boondi Raita",
"price": 110.0,
"category": "Salad Bar",
"available": true,
"veg": false,
"egg": false,
"restaurant": "9adafbd7-a9ba-4890-b707-c9d619c72f02",
"quantity": 1
}
],
"total_amount": 215.0
}
Snippet for Mapping Logic:
CartItem _items = CartItem(
couponCode: '',
deliveryStatus: false,
totalAmount: 0.0,
);
CartItem get items {
return _items;
}
// ===============================Looks Here
List<MenuItem> _cartProducts = [];
List<MenuItem> get cartProducts {
return [..._cartProducts];
}
Future<void> getCart() async {
Map<String, String> header = {
'Content-type': 'application/json',
'Authorization': accessToken,
};
try {
final response = await http.get(apiURL + getCartURL, headers: header);
print(response.statusCode);
if (response.statusCode == 200) {
final res = jsonDecode(response.body) as Map<String, dynamic>;
if (res == null) {
return _items;
}
_items = CartItem(
deliveryStatus: res['delivery_status'],
couponCode: res['coupon_code'],
totalAmount: res['total_amount'],
);
// ===============================Looks Here
List<MenuItem> cartStuff = [];
res["cart"].forEach((cartData) {
cartStuff.add(
MenuItem(
foodItemId: cartData['food_item_id'],
category: cartData['category'],
name: cartData['name'],
isAvailable: cartData['available'],
isEgg: cartData['egg'],
isVeg: cartData['veg'],
price: cartData['price'],
restaurant: cartData['restaurant'],
quantity: cartData['quantity'],
),
);
});
// ===============================Looks Here
_cartProducts = cartStuff;
print(_cartProducts);
notifyListeners();
} else if (response.statusCode == 403) {
fetchNewAToken().then((_) {
if (accessToken != null && refreshToken != null) getCart();
notifyListeners();
});
}
} catch (e) {
print("Error in getting the Cart");
print(e);
}
}
Snippet for displaying the data:
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import '../../globals/text_styles.dart';
import '../../globals/colors.dart';
import '../../providers/cart.dart';
class QuantityButton extends StatefulWidget {
//The item id received is correct so the error occurs is in accessing the data from the provider.
final itemID;
QuantityButton(this.itemID);
#override
_QuantityButtonState createState() => _QuantityButtonState();
}
class _QuantityButtonState extends State<QuantityButton> {
#override
Widget build(BuildContext context) {
final cartData = Provider.of<Cart>(context);
final cartQty =
cartData.cartProducts.where((item) => item.foodItemId == widget.itemID);
return Container(
width: 100,
height: 40,
child: Card(
color: primaryColor.withOpacity(0.9),
elevation: 0,
shape: RoundedRectangleBorder(
side: BorderSide(color: Colors.black),
borderRadius: BorderRadius.circular(10),
),
child: Row(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
GestureDetector(
onTap: () {
cartData.deleteItems(widget.itemID);
},
child: Icon(
Icons.arrow_left,
color: Colors.white,
size: 25,
),
),
Spacer(),
Container(
child: Padding(
padding: const EdgeInsets.all(3.0),
child: Text(
// =========== Print Quantity Here ===========
'',
style: valueTextStyle,
),
),
),
Spacer(),
GestureDetector(
onTap: () {
cartData.addItems(widget.itemID);
},
child: Icon(
Icons.arrow_right,
color: Colors.white,
size: 25,
),
),
],
),
),
);
}
}