Creating a cart app with GetIt

Let's create our cart application using GetIt. You will need to create a new Flutter app named cart_get_it, add a dependency for get_it and equatable from pub.dev, and copy the item.dart file from the previous section's code into your lib folder. Let's get started:

1. Create a new file named cart_model.dart and add the following code:

   import 'package:flutter/material.dart';
   import 'item.dart';
   import 'main.dart';
   // One
   class CartModel extends ChangeNotifier {
     // Two
     List<Item> items = populateItems();
     List<Item> cart = [];
     // Three
     void addItemToCart(Item item) {
       var newCart = <Item>[];
       newCart.addAll(cart);
       newCart.add(item);
       cart = newCart;
       notifyListeners();
     }
     removeItemFromCart(Item...