Add multiplayer counter sample

.github/workflows/test_dart.yml

@@ -38,6 +38,11 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
+      - name: Set up Flutter
+        uses: subosito/flutter-action@v2
+        with:
+          channel: 'stable'
+
       - name: Set up Dart ${{ matrix.dart-version }}
         uses: dart-lang/setup-dart@v1.6.0
         with:
@@ -49,7 +54,11 @@ jobs:
           for dir in $(find Dart -name pubspec.yaml -exec dirname {} \;); do
             echo "::group::Testing $dir"
             cd "$dir"
-            dart pub get
+            if grep -q "sdk: flutter" pubspec.yaml; then
+              flutter pub get
+            else
+              dart pub get
+            fi
             dart format --set-exit-if-changed .
             dart analyze .
             cd - > /dev/null

Dart/multi_counter/.gitignore

@@ -0,0 +1,9 @@
+.dart_tool
+.firebaserc
+.firebase
+*-debug.log
+
+app/.flutter-plugins-dependencies
+app/build
+
+server/bin/server

Dart/multi_counter/README.md

@@ -0,0 +1,10 @@
+# Multi-counter
+
+This is sample code from a talk at Cloud Next 2026.
+
+[Unify your tech stack with Dart](https://www.googlecloudevents.com/next-vegas/session-library?session_id=3911912&name=unify-your-tech-stack-with-dart)
+
+This sample contains three projects:
+- `app/` A Flutter application for a shared multi-counter.
+- `server/` A Cloud Functions for Firebase project containing functions for the multi-counter written in Dart.
+- `shared/` A shared Dart package containing logic and models used by both the app and the server.

Dart/multi_counter/analysis_options.yaml

@@ -0,0 +1,8 @@
+include: package:dart_flutter_team_lints/analysis_options.yaml
+
+linter:
+  rules:
+    - avoid_redundant_argument_values
+    - prefer_expression_function_bodies
+    - unnecessary_breaks
+    - unnecessary_ignore

Dart/multi_counter/app/.metadata

@@ -0,0 +1,30 @@
+# This file tracks properties of this Flutter project.
+# Used by Flutter tool to assess capabilities and perform upgrades etc.
+#
+# This file should be version controlled and should not be manually edited.
+
+version:
+  revision: "0c2d316b1565bc97fcf6125fa87dfb90ef05ed8f"
+  channel: "main"
+
+project_type: app
+
+# Tracks metadata for the flutter migrate command
+migration:
+  platforms:
+    - platform: root
+      create_revision: 0c2d316b1565bc97fcf6125fa87dfb90ef05ed8f
+      base_revision: 0c2d316b1565bc97fcf6125fa87dfb90ef05ed8f
+    - platform: web
+      create_revision: 0c2d316b1565bc97fcf6125fa87dfb90ef05ed8f
+      base_revision: 0c2d316b1565bc97fcf6125fa87dfb90ef05ed8f
+
+  # User provided section
+
+  # List of Local paths (relative to this file) that should be
+  # ignored by the migrate tool.
+  #
+  # Files that are not part of the templates will be ignored by default.
+  unmanaged_files:
+    - 'lib/main.dart'
+    - 'ios/Runner.xcodeproj/project.pbxproj'

Dart/multi_counter/app/lib/firebase_options.dart

@@ -0,0 +1,23 @@
+// File generated by FlutterFire CLI.
+// ignore_for_file: type=lint
+import 'package:firebase_core/firebase_core.dart' show FirebaseOptions;
+import 'package:flutter/foundation.dart' show defaultTargetPlatform, kIsWeb;
+
+/// Default [FirebaseOptions] for use with your Firebase apps.
+///
+/// Example:
+/// ```dart
+/// import 'firebase_options.dart';
+/// // ...
+/// await Firebase.initializeApp(
+///   options: DefaultFirebaseOptions.currentPlatform,
+/// );
+/// ```
+class DefaultFirebaseOptions {
+  static FirebaseOptions get currentPlatform {
+    throw UnsupportedError(
+      'DefaultFirebaseOptions have not been configured for $defaultTargetPlatform - '
+      'you can reconfigure this by running the FlutterFire CLI again.',
+    );
+  }
+}

Dart/multi_counter/app/lib/main.dart

@@ -0,0 +1,12 @@
+import 'package:flutter/material.dart';
+
+import 'src/app.dart';
+import 'src/config_state.dart';
+
+void main() async {
+  WidgetsFlutterBinding.ensureInitialized();
+
+  await initializeWorld();
+
+  runApp(const MyApp());
+}

Dart/multi_counter/app/lib/src/app.dart

@@ -0,0 +1,42 @@
+import 'package:flutter/material.dart';
+
+import 'router.dart';
+
+class MyApp extends StatelessWidget {
+  const MyApp({super.key});
+
+  @override
+  Widget build(BuildContext context) => MaterialApp.router(
+    debugShowCheckedModeBanner: false,
+    title: 'Flutter Demo',
+    routerConfig: router,
+    theme: ThemeData(
+      useMaterial3: true,
+      colorScheme: const ColorScheme.light(
+        primary: Color(0xFF18181B), // Zinc 900
+        secondary: Color(0xFF3F3F46), // Zinc 700
+        onSecondary: Colors.white,
+      ),
+      appBarTheme: const AppBarTheme(
+        backgroundColor: Colors.white,
+        foregroundColor: Color(0xFF18181B),
+        elevation: 0,
+      ),
+    ),
+    darkTheme: ThemeData(
+      useMaterial3: true,
+      colorScheme: const ColorScheme.dark(
+        primary: Color(0xFFFAFAFA), // Zinc 50
+        secondary: Color(0xFFD4D4D8), // Zinc 300
+        surface: Color(0xFF09090B), // Zinc 950
+        onPrimary: Color(0xFF18181B),
+        onSecondary: Color(0xFF18181B),
+      ),
+      appBarTheme: const AppBarTheme(
+        backgroundColor: Color(0xFF09090B),
+        foregroundColor: Color(0xFFFAFAFA),
+        elevation: 0,
+      ),
+    ),
+  );
+}

Dart/multi_counter/app/lib/src/config_state.dart

@@ -0,0 +1,34 @@
+import 'package:cloud_firestore/cloud_firestore.dart';
+import 'package:cloud_functions/cloud_functions.dart';
+import 'package:firebase_auth/firebase_auth.dart';
+import 'package:firebase_core/firebase_core.dart';
+import 'package:flutter/foundation.dart';
+import 'package:multi_counter_shared/multi_counter_shared.dart';
+
+import '../firebase_options.dart';
+
+Future<void> initializeWorld() async {
+  await Firebase.initializeApp(options: DefaultFirebaseOptions.currentPlatform);
+
+  if (kDebugMode) {
+    await FirebaseAuth.instance.useAuthEmulator('127.0.0.1', 9099);
+    FirebaseFirestore.instance.useFirestoreEmulator('127.0.0.1', 8080);
+    FirebaseFunctions.instance.useFunctionsEmulator('127.0.0.1', 5001);
+  }
+}
+
+final _options = HttpsCallableOptions(timeout: const Duration(seconds: 15));
+
+HttpsCallable get incrementHttpsCallable {
+  if (kDebugMode) {
+    return FirebaseFunctions.instance.httpsCallable(
+      incrementCallable,
+      options: _options,
+    );
+  } else {
+    return FirebaseFunctions.instance.httpsCallableFromUrl(
+      'https://increment-138342796561.us-central1.run.app',
+      options: _options,
+    );
+  }
+}

Dart/multi_counter/app/lib/src/constants.dart

@@ -0,0 +1,8 @@
+const appTitle = 'Multi-Counter';
+const maxContentWidth = 440.0;
+const double spaceSize = 16;
+const double doubleSpaceSize = spaceSize * 2;
+
+// TODO: Update this to the final example URI
+const githubDisplayUrl = 'github.com/kevmoo/next26_demo';
+final githubUri = Uri.parse('https://$githubDisplayUrl');

Dart/multi_counter/app/lib/src/router.dart

@@ -0,0 +1,48 @@
+import 'dart:async';
+
+import 'package:firebase_auth/firebase_auth.dart' hide EmailAuthProvider;
+import 'package:flutter/material.dart';
+import 'package:go_router/go_router.dart';
+
+import 'screens/counter/screen.dart';
+import 'screens/login.dart';
+
+final router = GoRouter(
+  initialLocation: '/',
+  routes: [
+    GoRoute(path: '/', builder: (context, state) => const CounterScreen()),
+    GoRoute(path: '/login', builder: (context, state) => const LoginScreen()),
+  ],
+  redirect: (context, state) async {
+    // Ensure we capture the redirect result before checking the auth state.
+    await FirebaseAuth.instance.getRedirectResult();
+
+    final loggedIn = FirebaseAuth.instance.currentUser != null;
+    final loggingIn = state.matchedLocation == '/login';
+
+    if (!loggedIn) return '/login';
+    if (loggingIn) return '/';
+
+    return null;
+  },
+  refreshListenable: GoRouterRefreshStream(
+    FirebaseAuth.instance.authStateChanges(),
+  ),
+);
+
+class GoRouterRefreshStream extends ChangeNotifier {
+  GoRouterRefreshStream(Stream<dynamic> stream) {
+    notifyListeners();
+    _subscription = stream.asBroadcastStream().listen(
+      (dynamic _) => notifyListeners(),
+    );
+  }
+
+  late final StreamSubscription<dynamic> _subscription;
+
+  @override
+  void dispose() {
+    _subscription.cancel();
+    super.dispose();
+  }
+}

Dart/multi_counter/app/lib/src/screens/counter/screen.dart

@@ -0,0 +1,109 @@
+import 'dart:async';
+
+import 'package:flutter/material.dart';
+import 'package:multi_counter_shared/multi_counter_shared.dart';
+
+import '../../constants.dart';
+import '../../widgets/app_scaffold.dart';
+import 'state.dart';
+
+class CounterScreen extends StatefulWidget {
+  const CounterScreen({super.key});
+
+  @override
+  State<CounterScreen> createState() => _CounterScreenState();
+}
+
+class _CounterScreenState extends State<CounterScreen> {
+  final state = CounterState();
+  late final StreamSubscription<IncrementResponse> _sub;
+  late final Listenable _merger;
+
+  @override
+  void initState() {
+    super.initState();
+
+    _merger = Listenable.merge([state.userCounter, state.globalCounter]);
+
+    ScaffoldFeatureController<SnackBar, SnackBarClosedReason>?
+    snackBarController;
+
+    _sub = state.incrementResponseStream.listen((response) {
+      if (!mounted) return;
+
+      final message = response.message;
+      if (message != null && snackBarController == null) {
+        snackBarController = ScaffoldMessenger.of(context).showSnackBar(
+          SnackBar(
+            content: Text(message),
+            backgroundColor: response.success ? null : Colors.red,
+          ),
+        );
+
+        snackBarController?.closed.then((reason) {
+          snackBarController = null;
+        });
+      }
+    });
+  }
+
+  @override
+  void dispose() {
+    _sub.cancel();
+    state.dispose();
+    super.dispose();
+  }
+
+  @override
+  Widget build(BuildContext context) => AppScaffold(
+    child: ListenableBuilder(
+      listenable: _merger,
+      builder: (context, child) {
+        final globalCount = state.globalCounter.value;
+        return SingleChildScrollView(
+          child: Column(
+            mainAxisSize: MainAxisSize.min,
+            mainAxisAlignment: MainAxisAlignment.center,
+            children: [
+              Text(
+                appTitle,
+                style: Theme.of(context).textTheme.headlineMedium,
+                textAlign: TextAlign.center,
+              ),
+              _spacer,
+              const Text('You have pushed the button this many times:'),
+              Text(
+                '${state.userCounter.value}',
+                style: Theme.of(context).textTheme.headlineMedium,
+              ),
+              _spacer,
+              if (globalCount == null) const Text('...'),
+              if (globalCount != null) ...[
+                const Text('Total button pushes:'),
+                Text(
+                  '${globalCount.totalClicks}',
+                  style: Theme.of(context).textTheme.headlineMedium,
+                ),
+                _spacer,
+                const Text('Total people who have pushed the button:'),
+                Text(
+                  '${globalCount.totalUsers}',
+                  style: Theme.of(context).textTheme.headlineMedium,
+                ),
+              ],
+              _spacer,
+              FloatingActionButton.extended(
+                onPressed: state.increment,
+                tooltip: 'Increment',
+                icon: const Icon(Icons.add),
+                label: const Text('Increment'),
+              ),
+            ],
+          ),
+        );
+      },
+    ),
+  );
+}
+
+const _spacer = SizedBox(height: doubleSpaceSize);