Add cart button

lib/app.dart

@@ -1,5 +1,8 @@
 import 'package:flutter/material.dart';
+import 'package:thesis_shop/route_key.dart';
+import 'package:thesis_shop/screens/cart/cart_screen.dart';
 import 'package:thesis_shop/screens/product_list/product_list_screen.dart';
+import 'package:thesis_shop/utils/map_keys_extension.dart';
 
 class ThesisShopApp extends StatelessWidget {
   const ThesisShopApp({Key? key}) : super(key: key);
@@ -13,7 +16,11 @@ class ThesisShopApp extends StatelessWidget {
         primarySwatch: Colors.red,
         brightness: Brightness.dark,
       ),
-      home: const ProductListScreen(),
+      routes: {
+        RouteKey.products: (context) => const ProductListScreen(),
+        RouteKey.cart: (context) => const CartScreen(),
+      }.mapKeys((key) => key.name),
+      initialRoute: 'products',
     );
   }
 }

lib/route_key.dart

@@ -0,0 +1,7 @@
+import 'package:flutter/widgets.dart';
+
+enum RouteKey { products, cart }
+
+extension NavigatorHelper on NavigatorState {
+  pushRouteKey(RouteKey key) => pushNamed(key.name);
+}

lib/screens/cart/cart_screen.dart

@@ -0,0 +1,12 @@
+import 'package:flutter/material.dart';
+
+class CartScreen extends StatelessWidget {
+  const CartScreen({Key? key}) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(title: const Text('Warenkorb')),
+    );
+  }
+}

lib/screens/product_list/cart_button.dart

@@ -0,0 +1,15 @@
+import 'package:flutter/material.dart';
+import 'package:thesis_shop/route_key.dart';
+
+class CartButton extends StatelessWidget {
+  const CartButton({Key? key}) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return ElevatedButton.icon(
+      onPressed: () => Navigator.of(context).pushRouteKey(RouteKey.cart),
+      icon: const Icon(Icons.shopping_basket),
+      label: const Text('Warenkorb (2 Produkte)'),
+    );
+  }
+}

lib/screens/product_list/cart_button_overlay.dart

@@ -0,0 +1,23 @@
+import 'package:flutter/material.dart';
+
+import 'cart_button.dart';
+
+class CartButtonOverlay extends StatelessWidget {
+  final Widget child;
+  const CartButtonOverlay({Key? key, required this.child}) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return Stack(
+      children: [
+        Positioned.fill(child: child),
+        const Positioned(
+          left: 8,
+          bottom: 8,
+          right: 8,
+          child: SafeArea(child: CartButton()),
+        )
+      ],
+    );
+  }
+}

lib/screens/product_list/product_list.dart

@@ -0,0 +1,18 @@
+import 'package:flutter/material.dart';
+import 'package:thesis_shop/models/product.dart';
+
+import 'product_item.dart';
+
+class ProductList extends StatelessWidget {
+  final List<Product> products;
+  const ProductList({Key? key, required this.products}) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return ListView.separated(
+      itemCount: products.length,
+      itemBuilder: (context, index) => ProductItem(product: products[index]),
+      separatorBuilder: (context, _) => const Divider(),
+    );
+  }
+}

lib/screens/product_list/product_list_screen.dart

@@ -1,6 +1,8 @@
 import 'package:flutter/material.dart';
 import 'package:thesis_shop/models/product.dart';
-import 'package:thesis_shop/screens/product_list/product_item.dart';
+
+import 'cart_button_overlay.dart';
+import 'product_list.dart';
 
 const _productPlaceholder = [
   Product(title: 'Bananen', price: 3),
@@ -17,10 +19,8 @@ class ProductListScreen extends StatelessWidget {
     const products = _productPlaceholder;
     return Scaffold(
       appBar: AppBar(title: const Text('Thesis Shop')),
-      body: ListView.separated(
-        itemCount: products.length,
-        itemBuilder: (context, index) => ProductItem(product: products[index]),
-        separatorBuilder: (context, _) => const Divider(),
+      body: const CartButtonOverlay(
+        child: ProductList(products: _productPlaceholder),
       ),
     );
   }

lib/utils/map_keys_extension.dart

@@ -0,0 +1,6 @@
+typedef MapFunction<T, K> = T Function(K key);
+
+extension MapKeysExtension<K, V> on Map<K, V> {
+  Map<T, V> mapKeys<T>(MapFunction<T, K> keyMapper) =>
+      map((key, value) => MapEntry(keyMapper(key), value));
+}