refactor(flutter_firebase_login): use emit.onEach in AppBloc (#4223)

Co-authored-by: Felix Angelov <[email protected]>

docs/src/content/docs/tutorials/flutter-firebase-login.mdx

@@ -159,7 +159,7 @@ The `AppBloc` is responsible for managing the global state of the application. I
 
 ### State
 
-The `AppState` consists of an `AppStatus` and a `User`. Two named constructors are exposed: `unauthenticated` and `authenticated` to make it easier to work with.
+The `AppState` consists of an `AppStatus` and a `User`. The default constructor accepts an optional `User` and redirects to the private constructor with the appropriate authentication status.
 
 <RemoteCode
 	url="https://raw.githubusercontent.com/felangel/bloc/master/examples/flutter_firebase_login/lib/app/bloc/app_state.dart"
@@ -170,8 +170,8 @@ The `AppState` consists of an `AppStatus` and a `User`. Two named constructors a
 
 The `AppEvent` has two subclasses:
 
-- `AppUserChanged` which notifies the bloc that the current user has changed.
-- `AppLogoutRequested` which notifies the bloc that the current user has requested to be logged out.
+- `AppUserSubscriptionRequested` which notifies the bloc to subscribe to the user stream.
+- `AppLogoutPressed` which notifies the bloc of a user logout action.
 
 <RemoteCode
 	url="https://raw.githubusercontent.com/felangel/bloc/master/examples/flutter_firebase_login/lib/app/bloc/app_event.dart"
@@ -180,10 +180,20 @@ The `AppEvent` has two subclasses:
 
 ### Bloc
 
-The `AppBloc` responds to incoming `AppEvents` and transforms them into outgoing `AppStates`. Upon initialization, it immediately subscribes to the `user` stream from the `AuthenticationRepository` and adds an `AuthenticationUserChanged` event internally to process changes in the current user.
+In the constructor body, `AppEvent` subclasses are mapped to their corresponding event handlers.
+
+In the `_onUserSubscriptionRequested` event handler, the `AppBloc` uses `emit.onEach` to subscribe to the user stream of the `AuthenticationRepository` and emit a state in response to each `User`.
+
+`emit.onEach` creates a stream subscription internally and takes care of canceling it when either `AppBloc` or the user stream is closed.
+
+If the user stream emits an error, `addError` forwards the error and stack trace to any `BlocObserver` listening.
 
 :::caution
-`close` is overridden in order to handle cancelling the internal `StreamSubscription`.
+If `onError` is omitted, any errors on the user stream are considered unhandled, and will be thrown by `onEach`. As a result, the subscription to the user stream will be canceled.
+:::
+
+:::tip
+A [`BlocObserver`](/bloc-concepts/#blocobserver-1) is great for logging Bloc events, errors, and state changes especially in the context analytics and crash reporting.
 :::
 
 <RemoteCode

examples/flutter_firebase_login/ios/Podfile

@@ -1,5 +1,5 @@
 # Uncomment this line to define a global platform for your project
-# platform :ios, '11.0'
+# platform :ios, '12.0'
 
 # CocoaPods analytics sends network stats synchronously affecting flutter build latency.
 ENV['COCOAPODS_DISABLE_STATS'] = 'true'
@@ -28,7 +28,6 @@ require File.expand_path(File.join('packages', 'flutter_tools', 'bin', 'podhelpe
 flutter_ios_podfile_setup
 
 target 'Runner' do
-  pod 'FirebaseFirestore', :git => 'https://github.com/invertase/firestore-ios-sdk-frameworks.git', :tag => $FirebaseSDKVersion
   use_frameworks!
   use_modular_headers!
 

examples/flutter_firebase_login/ios/Runner/AppDelegate.swift

@@ -1,7 +1,7 @@
 import UIKit
 import Flutter
 
-@UIApplicationMain
+@main
 @objc class AppDelegate: FlutterAppDelegate {
   override func application(
     _ application: UIApplication,

examples/flutter_firebase_login/lib/app/bloc/app_bloc.dart

@@ -10,36 +10,28 @@ part 'app_state.dart';
 class AppBloc extends Bloc<AppEvent, AppState> {
   AppBloc({required AuthenticationRepository authenticationRepository})
       : _authenticationRepository = authenticationRepository,
-        super(
-          authenticationRepository.currentUser.isNotEmpty
-              ? AppState.authenticated(authenticationRepository.currentUser)
-              : const AppState.unauthenticated(),
-        ) {
-    on<_AppUserChanged>(_onUserChanged);
-    on<AppLogoutRequested>(_onLogoutRequested);
-    _userSubscription = _authenticationRepository.user.listen(
-      (user) => add(_AppUserChanged(user)),
-    );
+        super(AppState(user: authenticationRepository.currentUser)) {
+    on<AppUserSubscriptionRequested>(_onUserSubscriptionRequested);
+    on<AppLogoutPressed>(_onLogoutPressed);
   }
 
   final AuthenticationRepository _authenticationRepository;
-  late final StreamSubscription<User> _userSubscription;
 
-  void _onUserChanged(_AppUserChanged event, Emitter<AppState> emit) {
-    emit(
-      event.user.isNotEmpty
-          ? AppState.authenticated(event.user)
-          : const AppState.unauthenticated(),
+  Future<void> _onUserSubscriptionRequested(
+    AppUserSubscriptionRequested event,
+    Emitter<AppState> emit,
+  ) {
+    return emit.onEach(
+      _authenticationRepository.user,
+      onData: (user) => emit(AppState(user: user)),
+      onError: addError,
     );
   }
 
-  void _onLogoutRequested(AppLogoutRequested event, Emitter<AppState> emit) {
-    unawaited(_authenticationRepository.logOut());
-  }
-
-  @override
-  Future<void> close() {
-    _userSubscription.cancel();
-    return super.close();
+  void _onLogoutPressed(
+    AppLogoutPressed event,
+    Emitter<AppState> emit,
+  ) {
+    _authenticationRepository.logOut();
   }
 }

examples/flutter_firebase_login/lib/app/bloc/app_event.dart

@@ -4,12 +4,10 @@ sealed class AppEvent {
   const AppEvent();
 }
 
-final class AppLogoutRequested extends AppEvent {
-  const AppLogoutRequested();
+final class AppUserSubscriptionRequested extends AppEvent {
+  const AppUserSubscriptionRequested();
 }
 
-final class _AppUserChanged extends AppEvent {
-  const _AppUserChanged(this.user);
-
-  final User user;
+final class AppLogoutPressed extends AppEvent {
+  const AppLogoutPressed();
 }

examples/flutter_firebase_login/lib/app/bloc/app_state.dart

@@ -1,20 +1,17 @@
 part of 'app_bloc.dart';
 
-enum AppStatus {
-  authenticated,
-  unauthenticated,
-}
+enum AppStatus { authenticated, unauthenticated }
 
 final class AppState extends Equatable {
-  const AppState._({
-    required this.status,
-    this.user = User.empty,
-  });
-
-  const AppState.authenticated(User user)
-      : this._(status: AppStatus.authenticated, user: user);
+  const AppState({User user = User.empty})
+      : this._(
+          status: user == User.empty
+              ? AppStatus.unauthenticated
+              : AppStatus.authenticated,
+          user: user,
+        );
 
-  const AppState.unauthenticated() : this._(status: AppStatus.unauthenticated);
+  const AppState._({required this.status, this.user = User.empty});
 
   final AppStatus status;
   final User user;

examples/flutter_firebase_login/lib/app/view/app.dart

@@ -18,9 +18,10 @@ class App extends StatelessWidget {
     return RepositoryProvider.value(
       value: _authenticationRepository,
       child: BlocProvider(
+        lazy: false,
         create: (_) => AppBloc(
           authenticationRepository: _authenticationRepository,
-        ),
+        )..add(const AppUserSubscriptionRequested()),
         child: const AppView(),
       ),
     );

examples/flutter_firebase_login/lib/home/view/home_page.dart

@@ -20,7 +20,7 @@ class HomePage extends StatelessWidget {
             key: const Key('homePage_logout_iconButton'),
             icon: const Icon(Icons.exit_to_app),
             onPressed: () {
-              context.read<AppBloc>().add(const AppLogoutRequested());
+              context.read<AppBloc>().add(const AppLogoutPressed());
             },
           ),
         ],

examples/flutter_firebase_login/packages/authentication_repository/lib/src/models/user.dart

@@ -29,12 +29,6 @@ class User extends Equatable {
   /// Empty user which represents an unauthenticated user.
   static const empty = User(id: '');
 
-  /// Convenience getter to determine whether the current user is empty.
-  bool get isEmpty => this == User.empty;
-
-  /// Convenience getter to determine whether the current user is not empty.
-  bool get isNotEmpty => this != User.empty;
-
   @override
   List<Object?> get props => [email, id, name, photo];
 }

examples/flutter_firebase_login/packages/authentication_repository/test/models/user_test.dart

@@ -13,23 +13,5 @@ void main() {
         equals(User(email: email, id: id)),
       );
     });
-
-    test('isEmpty returns true for empty user', () {
-      expect(User.empty.isEmpty, isTrue);
-    });
-
-    test('isEmpty returns false for non-empty user', () {
-      final user = User(email: email, id: id);
-      expect(user.isEmpty, isFalse);
-    });
-
-    test('isNotEmpty returns false for empty user', () {
-      expect(User.empty.isNotEmpty, isFalse);
-    });
-
-    test('isNotEmpty returns true for non-empty user', () {
-      final user = User(email: email, id: id);
-      expect(user.isNotEmpty, isTrue);
-    });
   });
 }

examples/flutter_firebase_login/packages/form_inputs/pubspec.yaml

@@ -6,4 +6,4 @@ environment:
   sdk: ">=3.0.0 <4.0.0"
 
 dependencies:
-  formz: ^0.6.0
+  formz: ^0.7.0

examples/flutter_firebase_login/pubspec.yaml

@@ -12,15 +12,15 @@ dependencies:
   bloc: ^8.1.0
   equatable: ^2.0.3
   firebase_core: ^3.0.0
-  flow_builder: ^0.0.9
+  flow_builder: ^0.1.0
   flutter:
     sdk: flutter
   flutter_bloc: ^8.1.1
   font_awesome_flutter: ^10.1.0
   form_inputs:
     path: packages/form_inputs
-  formz: ^0.6.0
-  google_fonts: ^4.0.0
+  formz: ^0.7.0
+  google_fonts: ^6.2.1
   meta: ^1.7.0
 
 dev_dependencies:

examples/flutter_firebase_login/test/app/bloc/app_bloc_test.dart

@@ -11,69 +11,68 @@ class MockAuthenticationRepository extends Mock
 class MockUser extends Mock implements User {}
 
 void main() {
-  group('AppBloc', () {
+  group(AppBloc, () {
     final user = MockUser();
     late AuthenticationRepository authenticationRepository;
 
     setUp(() {
       authenticationRepository = MockAuthenticationRepository();
       when(() => authenticationRepository.user).thenAnswer(
-        (_) => Stream.empty(),
+        (_) => const Stream.empty(),
       );
       when(
         () => authenticationRepository.currentUser,
-      ).thenReturn(User.empty);
+      ).thenReturn(user);
     });
 
-    test('initial state is unauthenticated when user is empty', () {
-      expect(
-        AppBloc(authenticationRepository: authenticationRepository).state,
-        AppState.unauthenticated(),
+    AppBloc buildBloc() {
+      return AppBloc(
+        authenticationRepository: authenticationRepository,
       );
+    }
+
+    test('initial state is $AppState', () {
+      expect(buildBloc().state, equals(AppState(user: user)));
     });
 
-    group('UserChanged', () {
+    group(AppUserSubscriptionRequested, () {
+      final error = Exception('oops');
+
       blocTest<AppBloc, AppState>(
-        'emits authenticated when user is not empty',
+        'emits $AppState when user stream emits a new value',
         setUp: () {
-          when(() => user.isNotEmpty).thenReturn(true);
           when(() => authenticationRepository.user).thenAnswer(
             (_) => Stream.value(user),
           );
         },
-        build: () => AppBloc(
-          authenticationRepository: authenticationRepository,
-        ),
-        seed: AppState.unauthenticated,
-        expect: () => [AppState.authenticated(user)],
+        build: buildBloc,
+        act: (bloc) => bloc.add(AppUserSubscriptionRequested()),
+        expect: () => [AppState(user: user)],
       );
 
       blocTest<AppBloc, AppState>(
-        'emits unauthenticated when user is empty',
+        'adds error when user stream emits an error',
         setUp: () {
-          when(() => authenticationRepository.user).thenAnswer(
-            (_) => Stream.value(User.empty),
-          );
+          when(
+            () => authenticationRepository.user,
+          ).thenAnswer((_) => Stream.error(error));
         },
-        build: () => AppBloc(
-          authenticationRepository: authenticationRepository,
-        ),
-        expect: () => [AppState.unauthenticated()],
+        build: buildBloc,
+        act: (bloc) => bloc.add(AppUserSubscriptionRequested()),
+        errors: () => [error],
       );
     });
 
-    group('LogoutRequested', () {
+    group(AppLogoutPressed, () {
       blocTest<AppBloc, AppState>(
         'invokes logOut',
         setUp: () {
           when(
             () => authenticationRepository.logOut(),
           ).thenAnswer((_) async {});
         },
-        build: () => AppBloc(
-          authenticationRepository: authenticationRepository,
-        ),
-        act: (bloc) => bloc.add(AppLogoutRequested()),
+        build: buildBloc,
+        act: (bloc) => bloc.add(AppLogoutPressed()),
         verify: (_) {
           verify(() => authenticationRepository.logOut()).called(1);
         },

examples/flutter_firebase_login/test/app/bloc/app_state_test.dart

@@ -7,22 +7,20 @@ import 'package:mocktail/mocktail.dart';
 class MockUser extends Mock implements User {}
 
 void main() {
-  group('AppState', () {
-    group('unauthenticated', () {
-      test('has correct status', () {
-        final state = AppState.unauthenticated();
-        expect(state.status, AppStatus.unauthenticated);
-        expect(state.user, User.empty);
-      });
+  group(AppState, () {
+    test(
+        'returns state with status unauthenticated '
+        'when user is empty', () {
+      expect(AppState().status, equals(AppStatus.unauthenticated));
     });
 
-    group('authenticated', () {
-      test('has correct status', () {
-        final user = MockUser();
-        final state = AppState.authenticated(user);
-        expect(state.status, AppStatus.authenticated);
-        expect(state.user, user);
-      });
+    test(
+        'returns state with status authenticated and user '
+        'when user is not empty', () {
+      final user = MockUser();
+      final state = AppState(user: user);
+      expect(state.status, equals(AppStatus.authenticated));
+      expect(state.user, equals(user));
     });
   });
 }