[compass_app] Scope LogoutViewModel to route builder — fix #2604 (#2819)

## Description

**Problem:** `LogoutViewModel` was built inside `HomeHeader.build()`, so
each rebuild could create a new instance and a new `logout` command.
That does not match how other Compass view models are scoped (created in
the GoRouter route `builder` and passed in), and it can affect an
in-flight logout when the home screen rebuilds.

**Change:** Create `LogoutViewModel` once in the `/home` route next to
`HomeViewModel`, pass it through `HomeScreen` → `HomeHeader` →
`LogoutButton`, and remove inline construction in `home_title.dart`.
Update `home_screen_test.dart` to build `LogoutViewModel` with fakes and
remove `Provider` wrappers that only supported `context.read()` in the
header.

**Result:** Logout view model lifetime aligns with the home route; no
visual or copy changes (screenshots not needed).

Fixes https://github.com/flutter/samples/issues/2604

---

## Pre-launch Checklist

- [x] I read the [Flutter Style Guide] _recently_, and have followed its
advice.
- [x] I signed the [CLA].
- [x] I read the [Contributors Guide].
- [x] I have added sample code updates to the [changelog].
- [x] I updated/added relevant documentation (doc comments with `///`).

If you need help, consider asking for advice on the #hackers-devrel
channel on [Discord].

<!-- Links -->
[Flutter Style Guide]:
https://github.com/flutter/flutter/blob/master/docs/contributing/Style-guide-for-Flutter-repo.md
[CLA]: https://cla.developers.google.com/
[Discord]:
https://github.com/flutter/flutter/blob/master/docs/contributing/Chat.md
[Contributors Guide]:
https://github.com/flutter/samples/blob/main/CONTRIBUTING.md
[changelog]: ../CHANGELOG.md

---------

Co-authored-by: Eric Windmill <eric@ericwindmill.com>

CHANGELOG.md

@@ -0,0 +1,10 @@
+# Changelog
+
+Notable changes to the samples in this repository are listed here.
+
+## [Unreleased]
+
+### compass_app
+
+* Scope `LogoutViewModel` to the home route so it is not recreated on every
+  `HomeHeader` rebuild ([#2604](https://github.com/flutter/samples/issues/2604)).

compass_app/app/lib/routing/router.dart

@@ -11,6 +11,7 @@ import '../ui/activities/view_models/activities_viewmodel.dart';
 import '../ui/activities/widgets/activities_screen.dart';
 import '../ui/auth/login/view_models/login_viewmodel.dart';
 import '../ui/auth/login/widgets/login_screen.dart';
+import '../ui/auth/logout/view_models/logout_viewmodel.dart';
 import '../ui/booking/view_models/booking_viewmodel.dart';
 import '../ui/booking/widgets/booking_screen.dart';
 import '../ui/home/view_models/home_viewmodel.dart';
@@ -46,7 +47,14 @@ GoRouter router(AuthRepository authRepository) => GoRouter(
           bookingRepository: context.read(),
           userRepository: context.read(),
         );
-        return HomeScreen(viewModel: viewModel);
+        final logoutViewModel = LogoutViewModel(
+          authRepository: context.read(),
+          itineraryConfigRepository: context.read(),
+        );
+        return HomeScreen(
+          viewModel: viewModel,
+          logoutViewModel: logoutViewModel,
+        );
       },
       routes: [
         GoRoute(

compass_app/app/lib/ui/home/widgets/home_screen.dart

@@ -7,6 +7,7 @@ import 'package:go_router/go_router.dart';
 
 import '../../../domain/models/booking/booking_summary.dart';
 import '../../../routing/routes.dart';
+import '../../auth/logout/view_models/logout_viewmodel.dart';
 import '../../core/localization/applocalization.dart';
 import '../../core/themes/colors.dart';
 import '../../core/themes/dimens.dart';
@@ -18,9 +19,14 @@ import 'home_title.dart';
 const String bookingButtonKey = 'booking-button';
 
 class HomeScreen extends StatefulWidget {
-  const HomeScreen({super.key, required this.viewModel});
+  const HomeScreen({
+    super.key,
+    required this.viewModel,
+    required this.logoutViewModel,
+  });
 
   final HomeViewModel viewModel;
+  final LogoutViewModel logoutViewModel;
 
   @override
   State<HomeScreen> createState() => _HomeScreenState();
@@ -88,7 +94,10 @@ class _HomeScreenState extends State<HomeScreen> {
                         vertical: Dimens.of(context).paddingScreenVertical,
                         horizontal: Dimens.of(context).paddingScreenHorizontal,
                       ),
-                      child: HomeHeader(viewModel: widget.viewModel),
+                      child: HomeHeader(
+                        viewModel: widget.viewModel,
+                        logoutViewModel: widget.logoutViewModel,
+                      ),
                     ),
                   ),
                   SliverList.builder(

compass_app/app/lib/ui/home/widgets/home_title.dart

@@ -4,7 +4,6 @@
 
 import 'package:flutter/material.dart';
 import 'package:google_fonts/google_fonts.dart';
-import 'package:provider/provider.dart';
 
 import '../../auth/logout/view_models/logout_viewmodel.dart';
 import '../../auth/logout/widgets/logout_button.dart';
@@ -13,9 +12,14 @@ import '../../core/themes/dimens.dart';
 import '../view_models/home_viewmodel.dart';
 
 class HomeHeader extends StatelessWidget {
-  const HomeHeader({super.key, required this.viewModel});
+  const HomeHeader({
+    super.key,
+    required this.viewModel,
+    required this.logoutViewModel,
+  });
 
   final HomeViewModel viewModel;
+  final LogoutViewModel logoutViewModel;
 
   @override
   Widget build(BuildContext context) {
@@ -37,12 +41,7 @@ class HomeHeader extends StatelessWidget {
                 height: Dimens.of(context).profilePictureSize,
               ),
             ),
-            LogoutButton(
+            LogoutButton(viewModel: logoutViewModel),
-              viewModel: LogoutViewModel(
-                authRepository: context.read(),
-                itineraryConfigRepository: context.read(),
-              ),
-            ),
           ],
         ),
         const SizedBox(height: Dimens.paddingVertical),

compass_app/app/test/ui/home/widgets/home_screen_test.dart

@@ -2,16 +2,14 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'package:compass_app/data/repositories/auth/auth_repository.dart';
-import 'package:compass_app/data/repositories/itinerary_config/itinerary_config_repository.dart';
 import 'package:compass_app/routing/routes.dart';
+import 'package:compass_app/ui/auth/logout/view_models/logout_viewmodel.dart';
 import 'package:compass_app/ui/home/view_models/home_viewmodel.dart';
 import 'package:compass_app/ui/home/widgets/home_screen.dart';
 import 'package:compass_app/utils/result.dart';
-import 'package:flutter/foundation.dart';
+import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:mocktail/mocktail.dart';
-import 'package:provider/provider.dart';
 
 import '../../../../testing/app.dart';
 import '../../../../testing/fakes/repositories/fake_auth_repository.dart';
@@ -24,6 +22,7 @@ import '../../../../testing/models/booking.dart';
 void main() {
   group('HomeScreen tests', () {
     late HomeViewModel viewModel;
+    late LogoutViewModel logoutViewModel;
     late MockGoRouter goRouter;
     late FakeBookingRepository bookingRepository;
 
@@ -33,6 +32,10 @@ void main() {
         bookingRepository: bookingRepository,
         userRepository: FakeUserRepository(),
       );
+      logoutViewModel = LogoutViewModel(
+        authRepository: FakeAuthRepository(),
+        itineraryConfigRepository: FakeItineraryConfigRepository(),
+      );
       goRouter = MockGoRouter();
       when(() => goRouter.push(any())).thenAnswer((_) => Future.value(null));
     });
@@ -40,12 +43,9 @@ void main() {
     Future<void> loadWidget(WidgetTester tester) async {
       await testApp(
         tester,
-        ChangeNotifierProvider.value(
+        HomeScreen(
-          value: FakeAuthRepository() as AuthRepository,
+          viewModel: viewModel,
-          child: Provider.value(
+          logoutViewModel: logoutViewModel,
-            value: FakeItineraryConfigRepository() as ItineraryConfigRepository,
-            child: HomeScreen(viewModel: viewModel),
-          ),
         ),
         goRouter: goRouter,
       );

cupertino_gallery/lib/widgets/sheet_page.dart

@@ -13,25 +13,20 @@ class SheetPage extends StatelessWidget {
           onPressed: () {
             Navigator.of(context).push(
               CupertinoSheetRoute<void>(
-                scrollableBuilder:
+                builder: (BuildContext context) {
-                    (BuildContext context, ScrollController controller) {
+                  return CupertinoPageScaffold(
-                      Widget widgetBuilder(BuildContext context) {
+                    navigationBar: CupertinoNavigationBar(
-                        return CupertinoPageScaffold(
+                      middle: const Text('Sheet'),
-                          navigationBar: CupertinoNavigationBar(
+                      trailing: GestureDetector(
-                            middle: const Text('Sheet'),
+                        child: const Icon(CupertinoIcons.xmark),
-                            trailing: GestureDetector(
+                        onTap: () {
-                              child: const Icon(CupertinoIcons.xmark),
+                          Navigator.of(context).pop();
-                              onTap: () {
+                        },
-                                Navigator.of(context).pop();
+                      ),
-                              },
+                    ),
-                            ),
+                    child: const Center(child: Text('This is a sheet')),
-                          ),
+                  );
-                          child: const Center(child: Text('This is a sheet')),
+                },
-                        );
-                      }
-
-                      return widgetBuilder(context);
-                    },
               ),
             );
           },