platform_design: Enforce use_key_in_widget_constructors (#927)

platform_design/lib/main.dart

@@ -11,9 +11,11 @@ import 'settings_tab.dart';
 import 'songs_tab.dart';
 import 'widgets.dart';
 
-void main() => runApp(MyAdaptingApp());
+void main() => runApp(const MyAdaptingApp());
 
 class MyAdaptingApp extends StatelessWidget {
+  const MyAdaptingApp({Key? key}) : super(key: key);
+
   @override
   Widget build(context) {
     // Either Material or Cupertino widgets work in either Material or Cupertino
@@ -34,6 +36,7 @@ class MyAdaptingApp extends StatelessWidget {
           child: Material(child: child),
         );
       },
+      // ignore: use_key_in_widget_constructors
       home: PlatformAdaptingHomePage(),
     );
   }
@@ -47,6 +50,8 @@ class MyAdaptingApp extends StatelessWidget {
 // These differences are also subjective and have more than one 'right' answer
 // depending on the app and content.
 class PlatformAdaptingHomePage extends StatefulWidget {
+  const PlatformAdaptingHomePage({Key? key}) : super(key: key);
+
   @override
   _PlatformAdaptingHomePageState createState() =>
       _PlatformAdaptingHomePageState();
@@ -107,12 +112,12 @@ class _PlatformAdaptingHomePageState extends State<PlatformAdaptingHomePage> {
           case 1:
             return CupertinoTabView(
               defaultTitle: NewsTab.title,
-              builder: (context) => NewsTab(),
+              builder: (context) => const NewsTab(),
             );
           case 2:
             return CupertinoTabView(
               defaultTitle: ProfileTab.title,
-              builder: (context) => ProfileTab(),
+              builder: (context) => const ProfileTab(),
             );
           default:
             assert(false, 'Unexpected tab');
@@ -161,8 +166,8 @@ class _AndroidDrawer extends StatelessWidget {
             title: const Text(NewsTab.title),
             onTap: () {
               Navigator.pop(context);
-              Navigator.push<void>(
-                  context, MaterialPageRoute(builder: (context) => NewsTab()));
+              Navigator.push<void>(context,
+                  MaterialPageRoute(builder: (context) => const NewsTab()));
             },
           ),
           ListTile(
@@ -171,7 +176,7 @@ class _AndroidDrawer extends StatelessWidget {
             onTap: () {
               Navigator.pop(context);
               Navigator.push<void>(context,
-                  MaterialPageRoute(builder: (context) => ProfileTab()));
+                  MaterialPageRoute(builder: (context) => const ProfileTab()));
             },
           ),
           // Long drawer contents are often segmented.
@@ -185,7 +190,7 @@ class _AndroidDrawer extends StatelessWidget {
             onTap: () {
               Navigator.pop(context);
               Navigator.push<void>(context,
-                  MaterialPageRoute(builder: (context) => SettingsTab()));
+                  MaterialPageRoute(builder: (context) => const SettingsTab()));
             },
           ),
         ],

platform_design/lib/news_tab.dart

@@ -15,6 +15,8 @@ class NewsTab extends StatefulWidget {
   static const androidIcon = Icon(Icons.library_books);
   static const iosIcon = Icon(CupertinoIcons.news);
 
+  const NewsTab({Key? key}) : super(key: key);
+
   @override
   _NewsTabState createState() => _NewsTabState();
 }

platform_design/lib/profile_tab.dart

@@ -13,6 +13,8 @@ class ProfileTab extends StatelessWidget {
   static const androidIcon = Icon(Icons.person);
   static const iosIcon = Icon(CupertinoIcons.profile_circled);
 
+  const ProfileTab({Key? key}) : super(key: key);
+
   Widget _buildBody(BuildContext context) {
     return SafeArea(
       child: Padding(
@@ -55,7 +57,7 @@ class ProfileTab extends StatelessWidget {
             Expanded(
               child: Container(),
             ),
-            LogOutButton(),
+            const LogOutButton(),
           ],
         ),
       ),
@@ -89,7 +91,7 @@ class ProfileTab extends StatelessWidget {
               CupertinoPageRoute(
                 title: SettingsTab.title,
                 fullscreenDialog: true,
-                builder: (context) => SettingsTab(),
+                builder: (context) => const SettingsTab(),
               ),
             );
           },
@@ -113,7 +115,8 @@ class PreferenceCard extends StatelessWidget {
     required this.header,
     required this.content,
     required this.preferenceChoices,
-  });
+    Key? key,
+  }) : super(key: key);
 
   final String header;
   final String content;
@@ -171,6 +174,8 @@ class LogOutButton extends StatelessWidget {
   static const _logoutMessage = Text(
       "You can't actually log out! This is just a demo of how alerts work.");
 
+  const LogOutButton({Key? key}) : super(key: key);
+
   // ===========================================================================
   // Non-shared code below because this tab shows different interfaces. On
   // Android, it's showing an alert dialog with 2 buttons and on iOS,

platform_design/lib/settings_tab.dart

@@ -12,6 +12,8 @@ class SettingsTab extends StatefulWidget {
   static const androidIcon = Icon(Icons.settings);
   static const iosIcon = Icon(CupertinoIcons.gear);
 
+  const SettingsTab({Key? key}) : super(key: key);
+
   @override
   _SettingsTabState createState() => _SettingsTabState();
 }

platform_design/lib/song_detail_tab.dart

@@ -16,7 +16,8 @@ class SongDetailTab extends StatelessWidget {
     required this.id,
     required this.song,
     required this.color,
-  });
+    Key? key,
+  }) : super(key: key);
 
   final int id;
   final String song;
@@ -71,7 +72,7 @@ class SongDetailTab extends StatelessWidget {
                   );
                 }
                 // Just a bunch of boxes that simulates loading song choices.
-                return SongPlaceholderTile();
+                return const SongPlaceholderTile();
               },
             ),
           ),

platform_design/lib/widgets.dart

@@ -41,7 +41,8 @@ class PressableCard extends StatefulWidget {
     required this.color,
     required this.flattenAnimation,
     this.child,
-  });
+    Key? key,
+  }) : super(key: key);
 
   final VoidCallback? onPressed;
   final Color color;
@@ -140,7 +141,8 @@ class HeroAnimatingSongCard extends StatelessWidget {
     required this.color,
     required this.heroAnimation,
     this.onPressed,
-  });
+    Key? key,
+  }) : super(key: key);
 
   final String song;
   final Color color;
@@ -218,6 +220,8 @@ class HeroAnimatingSongCard extends StatelessWidget {
 /// This is an example of a custom widget that an app developer might create for
 /// use on both iOS and Android as part of their brand's unique design.
 class SongPlaceholderTile extends StatelessWidget {
+  const SongPlaceholderTile({Key? key}) : super(key: key);
+
   @override
   Widget build(BuildContext context) {
     return SizedBox(