Merge pull request #55 from flutter-news-app-full-source-code/enhance-contenet-management-data-perfetching-performance

Enhance contenet management data perfetching performance

Author: fulleni

lib/app/view/app.dart

@@ -108,12 +108,14 @@ class App extends StatelessWidget {
               headlinesRepository: context.read<DataRepository<Headline>>(),
               topicsRepository: context.read<DataRepository<Topic>>(),
               sourcesRepository: context.read<DataRepository<Source>>(),
-            ),
+              countriesRepository: context.read<DataRepository<Country>>(),
+              languagesRepository: context.read<DataRepository<Language>>(),
+            )..add(const SharedDataRequested()),
           ),
           BlocProvider(
             create: (context) => DashboardBloc(
-              dashboardSummaryRepository:
-                  context.read<DataRepository<DashboardSummary>>(),
+              dashboardSummaryRepository: context
+                  .read<DataRepository<DashboardSummary>>(),
               headlinesRepository: context.read<DataRepository<Headline>>(),
               topicsRepository: context.read<DataRepository<Topic>>(),
               sourcesRepository: context.read<DataRepository<Source>>(),

lib/content_management/bloc/archived_headlines/archived_headlines_bloc.dart

@@ -12,8 +12,8 @@ class ArchivedHeadlinesBloc
     extends Bloc<ArchivedHeadlinesEvent, ArchivedHeadlinesState> {
   ArchivedHeadlinesBloc({
     required DataRepository<Headline> headlinesRepository,
-  })  : _headlinesRepository = headlinesRepository,
-        super(const ArchivedHeadlinesState()) {
+  }) : _headlinesRepository = headlinesRepository,
+       super(const ArchivedHeadlinesState()) {
     on<LoadArchivedHeadlinesRequested>(_onLoadArchivedHeadlinesRequested);
     on<RestoreHeadlineRequested>(_onRestoreHeadlineRequested);
     on<DeleteHeadlineForeverRequested>(_onDeleteHeadlineForeverRequested);

lib/content_management/bloc/archived_sources/archived_sources_bloc.dart

@@ -10,8 +10,8 @@ class ArchivedSourcesBloc
     extends Bloc<ArchivedSourcesEvent, ArchivedSourcesState> {
   ArchivedSourcesBloc({
     required DataRepository<Source> sourcesRepository,
-  })  : _sourcesRepository = sourcesRepository,
-        super(const ArchivedSourcesState()) {
+  }) : _sourcesRepository = sourcesRepository,
+       super(const ArchivedSourcesState()) {
     on<LoadArchivedSourcesRequested>(_onLoadArchivedSourcesRequested);
     on<RestoreSourceRequested>(_onRestoreSourceRequested);
   }

lib/content_management/bloc/archived_sources/archived_sources_state.dart

@@ -46,11 +46,11 @@ class ArchivedSourcesState extends Equatable {
 
   @override
   List<Object?> get props => [
-        status,
-        sources,
-        cursor,
-        hasMore,
-        exception,
-        restoredSource,
-      ];
+    status,
+    sources,
+    cursor,
+    hasMore,
+    exception,
+    restoredSource,
+  ];
 }

lib/content_management/bloc/archived_topics/archived_topics_bloc.dart

@@ -10,8 +10,8 @@ class ArchivedTopicsBloc
     extends Bloc<ArchivedTopicsEvent, ArchivedTopicsState> {
   ArchivedTopicsBloc({
     required DataRepository<Topic> topicsRepository,
-  })  : _topicsRepository = topicsRepository,
-        super(const ArchivedTopicsState()) {
+  }) : _topicsRepository = topicsRepository,
+       super(const ArchivedTopicsState()) {
     on<LoadArchivedTopicsRequested>(_onLoadArchivedTopicsRequested);
     on<RestoreTopicRequested>(_onRestoreTopicRequested);
   }

lib/content_management/bloc/archived_topics/archived_topics_state.dart

@@ -46,11 +46,11 @@ class ArchivedTopicsState extends Equatable {
 
   @override
   List<Object?> get props => [
-        status,
-        topics,
-        cursor,
-        hasMore,
-        exception,
-        restoredTopic,
-      ];
+    status,
+    topics,
+    cursor,
+    hasMore,
+    exception,
+    restoredTopic,
+  ];
 }

lib/content_management/bloc/content_management_bloc.dart

@@ -24,10 +24,15 @@ class ContentManagementBloc
     required DataRepository<Headline> headlinesRepository,
     required DataRepository<Topic> topicsRepository,
     required DataRepository<Source> sourcesRepository,
+    required DataRepository<Country> countriesRepository,
+    required DataRepository<Language> languagesRepository,
   }) : _headlinesRepository = headlinesRepository,
        _topicsRepository = topicsRepository,
        _sourcesRepository = sourcesRepository,
+       _countriesRepository = countriesRepository,
+       _languagesRepository = languagesRepository,
        super(const ContentManagementState()) {
+    on<SharedDataRequested>(_onSharedDataRequested);
     on<ContentManagementTabChanged>(_onContentManagementTabChanged);
     on<LoadHeadlinesRequested>(_onLoadHeadlinesRequested);
     on<HeadlineUpdated>(_onHeadlineUpdated);
@@ -43,6 +48,99 @@ class ContentManagementBloc
   final DataRepository<Headline> _headlinesRepository;
   final DataRepository<Topic> _topicsRepository;
   final DataRepository<Source> _sourcesRepository;
+  final DataRepository<Country> _countriesRepository;
+  final DataRepository<Language> _languagesRepository;
+
+  // --- Background Data Fetching for countries/languages for the ui Dropdown ---
+  //
+  // The DropdownButtonFormField widget does not natively support on-scroll
+  // pagination. To preserve UI consistency across the application, this BLoC
+  // employs an event-driven background fetching mechanism.
+  Future<void> _onSharedDataRequested(
+    SharedDataRequested event,
+    Emitter<ContentManagementState> emit,
+  ) async {
+    // Helper function to fetch all items of a given type.
+    Future<List<T>> fetchAll<T>({
+      required DataRepository<T> repository,
+      required List<SortOption> sort,
+    }) async {
+      final allItems = <T>[];
+      String? cursor;
+      bool hasMore;
+
+      do {
+        final response = await repository.readAll(
+          sort: sort,
+          pagination: PaginationOptions(cursor: cursor),
+          filter: {'status': ContentStatus.active.name},
+        );
+        allItems.addAll(response.items);
+        cursor = response.cursor;
+        hasMore = response.hasMore;
+      } while (hasMore);
+
+      return allItems;
+    }
+
+    // Check if data is already loaded or is currently loading to prevent
+    // redundant fetches.
+    if (state.allCountriesStatus == ContentManagementStatus.success &&
+        state.allLanguagesStatus == ContentManagementStatus.success) {
+      return;
+    }
+
+    // Set loading status for both lists.
+    emit(
+      state.copyWith(
+        allCountriesStatus: ContentManagementStatus.loading,
+        allLanguagesStatus: ContentManagementStatus.loading,
+      ),
+    );
+
+    try {
+      // Fetch both lists in parallel.
+      final results = await Future.wait([
+        fetchAll<Country>(
+          repository: _countriesRepository,
+          sort: [const SortOption('name', SortOrder.asc)],
+        ),
+        fetchAll<Language>(
+          repository: _languagesRepository,
+          sort: [const SortOption('name', SortOrder.asc)],
+        ),
+      ]);
+
+      final countries = results[0] as List<Country>;
+      final languages = results[1] as List<Language>;
+
+      // Update the state with the complete lists.
+      emit(
+        state.copyWith(
+          allCountries: countries,
+          allCountriesStatus: ContentManagementStatus.success,
+          allLanguages: languages,
+          allLanguagesStatus: ContentManagementStatus.success,
+        ),
+      );
+    } on HttpException catch (e) {
+      emit(
+        state.copyWith(
+          allCountriesStatus: ContentManagementStatus.failure,
+          allLanguagesStatus: ContentManagementStatus.failure,
+          exception: e,
+        ),
+      );
+    } catch (e) {
+      emit(
+        state.copyWith(
+          allCountriesStatus: ContentManagementStatus.failure,
+          allLanguagesStatus: ContentManagementStatus.failure,
+          exception: UnknownException('An unexpected error occurred: $e'),
+        ),
+      );
+    }
+  }
 
   void _onContentManagementTabChanged(
     ContentManagementTabChanged event,

lib/content_management/bloc/content_management_event.dart

@@ -155,3 +155,12 @@ final class SourceUpdated extends ContentManagementEvent {
   @override
   List<Object?> get props => [source];
 }
+
+/// {@template shared_data_requested}
+/// Event to request loading of shared data like countries and languages.
+/// This should be dispatched once when the content management section is loaded.
+/// {@endtemplate}
+final class SharedDataRequested extends ContentManagementEvent {
+  /// {@macro shared_data_requested}
+  const SharedDataRequested();
+}

lib/content_management/bloc/content_management_state.dart

@@ -32,6 +32,10 @@ class ContentManagementState extends Equatable {
     this.sources = const [],
     this.sourcesCursor,
     this.sourcesHasMore = false,
+    this.allCountriesStatus = ContentManagementStatus.initial,
+    this.allCountries = const [],
+    this.allLanguagesStatus = ContentManagementStatus.initial,
+    this.allLanguages = const [],
     this.exception,
   });
 
@@ -74,6 +78,18 @@ class ContentManagementState extends Equatable {
   /// Indicates if there are more sources to load.
   final bool sourcesHasMore;
 
+  /// Status of all countries data operations.
+  final ContentManagementStatus allCountriesStatus;
+
+  /// Cached list of all countries.
+  final List<Country> allCountries;
+
+  /// Status of all languages data operations.
+  final ContentManagementStatus allLanguagesStatus;
+
+  /// Cached list of all languages.
+  final List<Language> allLanguages;
+
   /// The error describing an operation failure, if any.
   final HttpException? exception;
 
@@ -92,6 +108,10 @@ class ContentManagementState extends Equatable {
     List<Source>? sources,
     String? sourcesCursor,
     bool? sourcesHasMore,
+    ContentManagementStatus? allCountriesStatus,
+    List<Country>? allCountries,
+    ContentManagementStatus? allLanguagesStatus,
+    List<Language>? allLanguages,
     HttpException? exception,
   }) {
     return ContentManagementState(
@@ -108,6 +128,10 @@ class ContentManagementState extends Equatable {
       sources: sources ?? this.sources,
       sourcesCursor: sourcesCursor ?? this.sourcesCursor,
       sourcesHasMore: sourcesHasMore ?? this.sourcesHasMore,
+      allCountriesStatus: allCountriesStatus ?? this.allCountriesStatus,
+      allCountries: allCountries ?? this.allCountries,
+      allLanguagesStatus: allLanguagesStatus ?? this.allLanguagesStatus,
+      allLanguages: allLanguages ?? this.allLanguages,
       exception: exception ?? this.exception,
     );
   }
@@ -127,6 +151,10 @@ class ContentManagementState extends Equatable {
     sources,
     sourcesCursor,
     sourcesHasMore,
+    allCountriesStatus,
+    allCountries,
+    allLanguagesStatus,
+    allLanguages,
     exception,
   ];
 }

lib/content_management/bloc/create_headline/create_headline_bloc.dart

@@ -8,10 +8,6 @@ import 'package:uuid/uuid.dart';
 part 'create_headline_event.dart';
 part 'create_headline_state.dart';
 
-final class _FetchNextCountryPage extends CreateHeadlineEvent {
-  const _FetchNextCountryPage();
-}
-
 /// A BLoC to manage the state of creating a new headline.
 class CreateHeadlineBloc
     extends Bloc<CreateHeadlineEvent, CreateHeadlineState> {
@@ -20,12 +16,11 @@ class CreateHeadlineBloc
     required DataRepository<Headline> headlinesRepository,
     required DataRepository<Source> sourcesRepository,
     required DataRepository<Topic> topicsRepository,
-    required DataRepository<Country> countriesRepository,
+    required List<Country> countries,
   }) : _headlinesRepository = headlinesRepository,
        _sourcesRepository = sourcesRepository,
        _topicsRepository = topicsRepository,
-       _countriesRepository = countriesRepository,
-       super(const CreateHeadlineState()) {
+       super(CreateHeadlineState(countries: countries)) {
     on<CreateHeadlineDataLoaded>(_onDataLoaded);
     on<CreateHeadlineTitleChanged>(_onTitleChanged);
     on<CreateHeadlineExcerptChanged>(_onExcerptChanged);
@@ -36,13 +31,11 @@ class CreateHeadlineBloc
     on<CreateHeadlineCountryChanged>(_onCountryChanged);
     on<CreateHeadlineStatusChanged>(_onStatusChanged);
     on<CreateHeadlineSubmitted>(_onSubmitted);
-    on<_FetchNextCountryPage>(_onFetchNextCountryPage);
   }
 
   final DataRepository<Headline> _headlinesRepository;
   final DataRepository<Source> _sourcesRepository;
   final DataRepository<Topic> _topicsRepository;
-  final DataRepository<Country> _countriesRepository;
   final _uuid = const Uuid();
 
   Future<void> _onDataLoaded(
@@ -65,26 +58,13 @@ class CreateHeadlineBloc
       final sources = (sourcesResponse as PaginatedResponse<Source>).items;
       final topics = (topicsResponse as PaginatedResponse<Topic>).items;
 
-      final countriesResponse = await _countriesRepository.readAll(
-        sort: [const SortOption('name', SortOrder.asc)],
-      );
-
       emit(
         state.copyWith(
           status: CreateHeadlineStatus.initial,
           sources: sources,
           topics: topics,
-          countries: countriesResponse.items,
-          countriesCursor: countriesResponse.cursor,
-          countriesHasMore: countriesResponse.hasMore,
         ),
       );
-
-      // After the initial page of countries is loaded, start a background
-      // process to fetch all remaining pages.
-      if (state.countriesHasMore) {
-        add(const _FetchNextCountryPage());
-      }
     } on HttpException catch (e) {
       emit(state.copyWith(status: CreateHeadlineStatus.failure, exception: e));
     } catch (e) {
@@ -159,49 +139,6 @@ class CreateHeadlineBloc
   }
 
   // --- Background Data Fetching for Dropdown ---
-  // The DropdownButtonFormField widget does not natively support on-scroll
-  // pagination. To preserve UI consistency across the application, this BLoC
-  // employs an event-driven background fetching mechanism.
-  //
-  // After the first page of items is loaded, a chain of events is initiated
-  // to progressively fetch all remaining pages. This process is throttled
-  // and runs in the background, ensuring the UI remains responsive while the
-  // full list of dropdown options is populated over time.
-  Future<void> _onFetchNextCountryPage(
-    _FetchNextCountryPage event,
-    Emitter<CreateHeadlineState> emit,
-  ) async {
-    if (!state.countriesHasMore || state.countriesIsLoadingMore) return;
-
-    try {
-      emit(state.copyWith(countriesIsLoadingMore: true));
-
-      // ignore: inference_failure_on_instance_creation
-      await Future.delayed(const Duration(milliseconds: 400));
-
-      final nextCountries = await _countriesRepository.readAll(
-        pagination: PaginationOptions(cursor: state.countriesCursor),
-        sort: [const SortOption('name', SortOrder.asc)],
-      );
-
-      emit(
-        state.copyWith(
-          countries: List.of(state.countries)..addAll(nextCountries.items),
-          countriesCursor: nextCountries.cursor,
-          countriesHasMore: nextCountries.hasMore,
-          countriesIsLoadingMore: false,
-        ),
-      );
-
-      if (nextCountries.hasMore) {
-        add(const _FetchNextCountryPage());
-      }
-    } catch (e) {
-      emit(state.copyWith(countriesIsLoadingMore: false));
-      // Optionally log the error without disrupting the user
-    }
-  }
-
   Future<void> _onSubmitted(
     CreateHeadlineSubmitted event,
     Emitter<CreateHeadlineState> emit,