Implement cart store for cart screen

lib/screens/cart/cart_screen.dart

@@ -1,22 +1,16 @@
 import 'package:flutter/material.dart';
-import 'package:thesis_shop/models/cart_item.dart';
-import 'package:thesis_shop/models/product.dart';
 import 'package:thesis_shop/screens/cart/total_price_text.dart';
+import 'package:thesis_shop/stores/cart_store.dart';
 import 'package:thesis_shop/widgets/user_switch.dart';
 
 import 'cart_item_list.dart';
 
-const _placeHolderItems = [
-  CartItem(product: Product(title: 'Äpfel', price: 3), amount: 3),
-  CartItem(product: Product(title: 'Äpfel', price: 3), amount: 3),
-  CartItem(product: Product(title: 'Äpfel', price: 3), amount: 3),
-];
-
 class CartScreen extends StatelessWidget {
   const CartScreen({Key? key}) : super(key: key);
 
   @override
   Widget build(BuildContext context) {
+    final cartStore = CartStore.of(context);
     return Scaffold(
       appBar: AppBar(
         title: const Text('Warenkorb'),
@@ -24,8 +18,8 @@ class CartScreen extends StatelessWidget {
       ),
       body: Column(
         mainAxisSize: MainAxisSize.max,
-        children: const [
-          Expanded(child: CartItemList(items: _placeHolderItems)),
+        children: [
+          Expanded(child: CartItemList(items: cartStore.cartItems)),
           TotalPriceText(),
         ],
       ),

lib/screens/cart/total_price_text.dart

@@ -1,15 +1,17 @@
 import 'package:flutter/material.dart';
+import 'package:thesis_shop/stores/cart_store.dart';
 
 class TotalPriceText extends StatelessWidget {
   const TotalPriceText({Key? key}) : super(key: key);
 
   @override
   Widget build(BuildContext context) {
+    final cartStore = CartStore.of(context);
     return SafeArea(
       child: Padding(
         padding: const EdgeInsets.all(8.0),
         child: Text(
-          'Gesamtpreis: 27€',
+          'Gesamtpreis: ${cartStore.totalPriceAsText}€',
           style: Theme.of(context).textTheme.labelLarge?.copyWith(fontSize: 24),
         ),
       ),

lib/stores/cart_store.dart

@@ -61,6 +61,11 @@ class CartStore extends InheritedWidget {
   final Function(Product) increaseAmount;
   final Function(Product) decreaseAmount;
 
+  String get totalPriceAsText => cartItems
+      .fold<double>(
+          0.0, (previousValue, item) => previousValue + item.totalPrice)
+      .toStringAsFixed(2);
+
   int amountOfProduct(Product product) {
     final amounts = {
       for (final item in cartItems) item.product: item.amount,