Add navigation with expanding sidebar.

namer_app/lib/main.dart

@@ -26,33 +26,128 @@ class MyApp extends StatelessWidget {
 }
 
 class MyAppState extends ChangeNotifier {
-  var current = WordPair.random();// ...
+  var current = WordPair.random();
 
-  // ↓ Add this.
   void getNext() {
     current = WordPair.random();
     notifyListeners();
   }
+
+  var favorites = <WordPair>[];
+
+  void toggleFavorite() {
+    if (favorites.contains(current)) {
+      favorites.remove(current);
+    } else {
+      favorites.add(current);
+    }
+    notifyListeners();
+    print("Favorites are: ${favorites.toString()}");
+  }
 }
 
-class MyHomePage extends StatelessWidget {
+class MyHomePage extends StatefulWidget {
+  @override
+  State<MyHomePage> createState() => _MyHomePageState();
+}
+
+class _MyHomePageState extends State<MyHomePage> {
+
+  var selectedIndex = 0;
+
+  @override
+  Widget build(BuildContext context) {
+
+    Widget page;
+    switch (selectedIndex) {
+      case 0:
+        page = GeneratorPage();
+        break;
+      case 1:
+        page = Placeholder();
+        break;
+      default:
+        throw UnimplementedError('no widget for $selectedIndex');
+    }
+
+    return LayoutBuilder(
+      builder: (context, constraints) {
+        return Scaffold(
+          body: Row(
+            children: [
+              SafeArea(
+                child: NavigationRail(
+                  extended: constraints.maxWidth >= 600,
+                  destinations: [
+                    NavigationRailDestination(
+                      icon: Icon(Icons.home),
+                      label: Text('Home'),
+                    ),
+                    NavigationRailDestination(
+                      icon: Icon(Icons.favorite),
+                      label: Text('Favorites'),
+                    ),
+                  ],
+                  selectedIndex: selectedIndex,
+                  onDestinationSelected: (value) {
+                    setState(() {
+                      selectedIndex = value;
+                    });
+                  }
+                ),
+              ),
+              Expanded(
+                child: Container(
+                  color: Theme.of(context).colorScheme.primaryContainer,
+                  child: page,
+                ),
+              ),
+            ],
+          ),
+        );
+      }
+    );
+  }
+}
+
+class GeneratorPage extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     var appState = context.watch<MyAppState>();
     var pair = appState.current;
 
-    return Scaffold(
+    IconData icon;
-      body: Column(
+    if (appState.favorites.contains(pair)) {
-        children: [
+      icon = Icons.favorite;
-          Text('A random wordpair:'),
+    } else {
-          BigCard(pair: pair),
+      icon = Icons.favorite_border;
-          ElevatedButton(
+    }
-            onPressed: () {
-              appState.getNext();
-            },
-            child: Text('Next'),
-          ),
 
+    return Center(
+      child: Column(
+        mainAxisAlignment: MainAxisAlignment.center,
+        children: [
+          BigCard(pair: pair),
+          SizedBox(height: 10),
+          Row(
+            mainAxisSize: MainAxisSize.min,
+            children: [
+              ElevatedButton.icon(
+                onPressed: () {
+                  appState.toggleFavorite();
+                },
+                icon: Icon(icon),
+                label: Text('Like'),
+              ),
+              SizedBox(width: 10),
+              ElevatedButton(
+                onPressed: () {
+                  appState.getNext();
+                },
+                child: Text('Next'),
+              ),
+            ],
+          ),
         ],
       ),
     );
@@ -74,12 +169,15 @@ class BigCard extends StatelessWidget {
       color: theme.colorScheme.onPrimary,
     );
 
-
     return Card(
       color: theme.colorScheme.primary,
       child: Padding(
         padding: const EdgeInsets.all(15.0),
-        child: Text(pair.asLowerCase, style: style),
+        child: Text(
+          pair.asLowerCase,
+          style: style,
+          semanticsLabel: "${pair.first} ${pair.second}",
+        ),
       ),
     );
   }