Upgrading samples to flutter_lints, part 1 of n (#804)

provider_shopper/lib/common/theme.dart

@@ -6,7 +6,7 @@ import 'package:flutter/material.dart';
 
 final appTheme = ThemeData(
   primarySwatch: Colors.yellow,
-  textTheme: TextTheme(
+  textTheme: const TextTheme(
     headline1: TextStyle(
       fontFamily: 'Corben',
       fontWeight: FontWeight.w700,

provider_shopper/lib/screens/cart.dart

@@ -24,7 +24,7 @@ class MyCart extends StatelessWidget {
                 child: _CartList(),
               ),
             ),
-            Divider(height: 4, color: Colors.black),
+            const Divider(height: 4, color: Colors.black),
             _CartTotal()
           ],
         ),
@@ -45,9 +45,9 @@ class _CartList extends StatelessWidget {
     return ListView.builder(
       itemCount: cart.items.length,
       itemBuilder: (context, index) => ListTile(
-        leading: Icon(Icons.done),
+        leading: const Icon(Icons.done),
         trailing: IconButton(
-          icon: Icon(Icons.remove_circle_outline),
+          icon: const Icon(Icons.remove_circle_outline),
           onPressed: () {
             cart.remove(cart.items[index]);
           },
@@ -82,14 +82,14 @@ class _CartTotal extends StatelessWidget {
             Consumer<CartModel>(
                 builder: (context, cart, child) =>
                     Text('\$${cart.totalPrice}', style: hugeStyle)),
-            SizedBox(width: 24),
+            const SizedBox(width: 24),
             TextButton(
               onPressed: () {
                 ScaffoldMessenger.of(context).showSnackBar(
-                    SnackBar(content: Text('Buying not supported yet.')));
+                    const SnackBar(content: Text('Buying not supported yet.')));
               },
               style: TextButton.styleFrom(primary: Colors.white),
-              child: Text('BUY'),
+              child: const Text('BUY'),
             ),
           ],
         ),

provider_shopper/lib/screens/catalog.dart

@@ -14,7 +14,7 @@ class MyCatalog extends StatelessWidget {
       body: CustomScrollView(
         slivers: [
           _MyAppBar(),
-          SliverToBoxAdapter(child: SizedBox(height: 12)),
+          const SliverToBoxAdapter(child: SizedBox(height: 12)),
           SliverList(
             delegate: SliverChildBuilderDelegate(
                 (context, index) => _MyListItem(index)),
@@ -62,7 +62,9 @@ class _AddButton extends StatelessWidget {
           return null; // Defer to the widget's default.
         }),
       ),
-      child: isInCart ? Icon(Icons.check, semanticLabel: 'ADDED') : Text('ADD'),
+      child: isInCart
+          ? const Icon(Icons.check, semanticLabel: 'ADDED')
+          : const Text('ADD'),
     );
   }
 }
@@ -75,7 +77,7 @@ class _MyAppBar extends StatelessWidget {
       floating: true,
       actions: [
         IconButton(
-          icon: Icon(Icons.shopping_cart),
+          icon: const Icon(Icons.shopping_cart),
           onPressed: () => Navigator.pushNamed(context, '/cart'),
         ),
       ],
@@ -86,7 +88,7 @@ class _MyAppBar extends StatelessWidget {
 class _MyListItem extends StatelessWidget {
   final int index;
 
-  _MyListItem(this.index, {Key? key}) : super(key: key);
+  const _MyListItem(this.index, {Key? key}) : super(key: key);
 
   @override
   Widget build(BuildContext context) {
@@ -109,11 +111,11 @@ class _MyListItem extends StatelessWidget {
                 color: item.color,
               ),
             ),
-            SizedBox(width: 24),
+            const SizedBox(width: 24),
             Expanded(
               child: Text(item.name, style: textTheme),
             ),
-            SizedBox(width: 24),
+            const SizedBox(width: 24),
             _AddButton(item: item),
           ],
         ),

provider_shopper/lib/screens/login.dart

@@ -10,7 +10,7 @@ class MyLogin extends StatelessWidget {
     return Scaffold(
       body: Center(
         child: Container(
-          padding: EdgeInsets.all(80.0),
+          padding: const EdgeInsets.all(80.0),
           child: Column(
             mainAxisAlignment: MainAxisAlignment.center,
             children: [
@@ -19,21 +19,21 @@ class MyLogin extends StatelessWidget {
                 style: Theme.of(context).textTheme.headline1,
               ),
               TextFormField(
-                decoration: InputDecoration(
+                decoration: const InputDecoration(
                   hintText: 'Username',
                 ),
               ),
               TextFormField(
-                decoration: InputDecoration(
+                decoration: const InputDecoration(
                   hintText: 'Password',
                 ),
                 obscureText: true,
               ),
-              SizedBox(
+              const SizedBox(
                 height: 24,
               ),
               ElevatedButton(
-                child: Text('ENTER'),
+                child: const Text('ENTER'),
                 onPressed: () {
                   Navigator.pushReplacementNamed(context, '/catalog');
                 },