remove navigation rail, update adaptive scaffold (#404)

experimental/web_dashboard/lib/src/app.dart

@@ -5,12 +5,20 @@
 import 'package:flutter/material.dart';
 import 'package:provider/provider.dart';
 
-import 'pages/home.dart';
 import 'api/api.dart';
 import 'api/mock.dart';
+import 'pages/home.dart';
+import 'widgets/third_party/adaptive_scaffold.dart';
 
 /// An app that shows a responsive dashboard.
-class DashboardApp extends StatelessWidget {
+class DashboardApp extends StatefulWidget {
+  @override
+  _DashboardAppState createState() => _DashboardAppState();
+}
+
+class _DashboardAppState extends State<DashboardApp> {
+  int _pageIndex = 0;
+
   @override
   Widget build(BuildContext context) {
     return MultiProvider(
@@ -18,8 +26,34 @@ class DashboardApp extends StatelessWidget {
         Provider<DashboardApi>(create: (_) => MockDashboardApi()),
       ],
       child: MaterialApp(
-        home: HomePage(),
+        home: AdaptiveScaffold(
+          currentIndex: _pageIndex,
+          destinations: [
+            AdaptiveScaffoldDestination(title: 'Home', icon: Icons.home),
+            AdaptiveScaffoldDestination(title: 'Entries', icon: Icons.list),
+            AdaptiveScaffoldDestination(
+                title: 'Settings', icon: Icons.settings),
+          ],
+          body: _pageAtIndex(_pageIndex),
+          onNavigationIndexChange: (newIndex) {
+            setState(() {
+              _pageIndex = newIndex;
+            });
+          },
+        ),
       ),
     );
   }
+
+  static Widget _pageAtIndex(int index) {
+    switch (index) {
+      case 1:
+        return Center(child: Text('page 2'));
+      case 2:
+        return Center(child: Text('page 3'));
+      case 0:
+      default:
+        return HomePage();
+    }
+  }
 }