Converting a map into list of objects in flutter - flutter

Question

I'm pretty new to Flutter and still struggling to understand a few things. My objective right now is to place map objects inside a list the logic for which that I've written hasn't been kind. I would therefore need suggestions as to how this can be achieved. The code I've written by far is below:
class CartItemProvider with ChangeNotifier {
Map<String, dynamic> _cartItems = {};
var _cartItemList = [];
List<dynamic> _individualItems = [];
Network network = Network();
String baseUrl = 'https://achievexsolutions.in/current_work/eatiano/';
double deliveryCost = 40;
double discountCost = 50;
Map<String, dynamic> get cartItems {
return {..._cartItems};
}
Future<void> fetchCartItems() async {
final url = Uri.parse(baseUrl + 'api/auth/cart');
final response = await http.get(url, headers: {
'Authorization': 'Bearer ${network.getToken()}',
'Accept': 'application/json'
});
Cart cartJson = cartFromJson(response.body);
_cartItems = cartJson.toJson();
_cartItems.forEach((key, values) => _cartItemList.add(values['data']));
print(_cartItems);
}
}
The error that I get says Unhandled Exception: NoSuchMethodError: The method 'map' was called on null.
{
"status": "success",
"data": [
{
"cart_id": 9,
"restaurant_id": "6",
"product_id": "8",
"restaurant_name": "Mocambo",
"product_name": "Kaju Paneer",
"product_description": "Tasty yummy paneer gravy dish",
"product_image": "/public/assets/product/lgml5L03-19-41.jpg",
"product_selling_price": "320",
"product_status": "active",
"product_quantity": "41",
"product_rating": null,
"product_rating_count": null,
"product_sell_count": null,
"quantity": "1"
}
]
}
I would like to store the objects in the list named data which is my main priority. The model class for the above response is below:
import 'package:meta/meta.dart';
import 'dart:convert';
Cart cartFromJson(String str) => Cart.fromJson(json.decode(str));
String cartToJson(Cart data) => json.encode(data.toJson());
class Cart {
Cart({
required this.status,
required this.data,
});
String status;
List<Datum> data;
factory Cart.fromJson(Map<String, dynamic> json) => Cart(
status: json["status"],
data: List<Datum>.from(json["data"].map((x) => Datum.fromJson(x))),
);
Map<String, dynamic> toJson() => {
"status": status,
"data": List<dynamic>.from(data.map((x) => x.toJson())),
};
}
class Datum {
Datum({
required this.cartId,
required this.restaurantId,
required this.productId,
required this.restaurantName,
required this.productName,
required this.productDescription,
required this.productImage,
required this.productSellingPrice,
required this.productStatus,
required this.productQuantity,
required this.productRating,
required this.productRatingCount,
required this.productSellCount,
required this.quantity,
});
int cartId;
String restaurantId;
String productId;
String restaurantName;
String productName;
String productDescription;
String productImage;
String productSellingPrice;
String productStatus;
String productQuantity;
dynamic productRating;
dynamic productRatingCount;
dynamic productSellCount;
String quantity;
factory Datum.fromJson(Map<String, dynamic> json) => Datum(
cartId: json["cart_id"],
restaurantId: json["restaurant_id"],
productId: json["product_id"],
restaurantName: json["restaurant_name"],
productName: json["product_name"],
productDescription: json["product_description"],
productImage: json["product_image"],
productSellingPrice: json["product_selling_price"],
productStatus: json["product_status"],
productQuantity: json["product_quantity"],
productRating: json["product_rating"],
productRatingCount: json["product_rating_count"],
productSellCount: json["product_sell_count"],
quantity: json["quantity"],
);
Map<String, dynamic> toJson() => {
"cart_id": cartId,
"restaurant_id": restaurantId,
"product_id": productId,
"restaurant_name": restaurantName,
"product_name": productName,
"product_description": productDescription,
"product_image": productImage,
"product_selling_price": productSellingPrice,
"product_status": productStatus,
"product_quantity": productQuantity,
"product_rating": productRating,
"product_rating_count": productRatingCount,
"product_sell_count": productSellCount,
"quantity": quantity,
};
}

Answer 1

This three cases are likely the cause of your problem:
"product_rating": null,
"product_rating_count": null,
"product_sell_count": null,
because in your function below
Map<String, dynamic> toJson() => {
"status": status,
"data": List<dynamic>.from(data.map((x) => x.toJson())),
};
you're calling .map on a null object, hence the error. You have to handle somehow the cases where json["data"] is null before calling any method on it. Is your code null-safe? That might help in cases like this because I think the IDE would warn you of such nullable cases (at least, Android Studio does).