Add navigation with expanding sidebar.

namer_app/lib/main.dart

@@ -46,7 +46,71 @@ class MyAppState extends ChangeNotifier {
   }
 }
 
-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>();
@@ -59,13 +123,12 @@ class MyHomePage extends StatelessWidget {
       icon = Icons.favorite_border;
     }
 
-    return Scaffold(
+    return Center(
-      body: Center(
       child: Column(
         mainAxisAlignment: MainAxisAlignment.center,
         children: [
           BigCard(pair: pair),
-            SizedBox(height: 10.0), // Just a spacer.
+          SizedBox(height: 10),
           Row(
             mainAxisSize: MainAxisSize.min,
             children: [
@@ -74,11 +137,9 @@ class MyHomePage extends StatelessWidget {
                   appState.toggleFavorite();
                 },
                 icon: Icon(icon),
-                  label: Text('Favorite'),
+                label: Text('Like'),
               ),
-
+              SizedBox(width: 10),
-                SizedBox(width: 10.0),
-
               ElevatedButton(
                 onPressed: () {
                   appState.getNext();
@@ -89,7 +150,6 @@ class MyHomePage extends StatelessWidget {
           ),
         ],
       ),
-      ),
     );
   }
 }