I am new in this state management world. So I was trying to follow this tutorial (How to Save Products in a Wishlist using the BloC Pattern - EP10 - The eCommerce Series), but mapEventToState is deprecated so I am not sure what to do.
Here is my state:
part of 'wishlist_bloc.dart';
abstract class WishlistState extends Equatable {
const WishlistState();
#override
List<Object> get props => [];
}
class WishlistLoading extends WishlistState {}
class WishlistLoaded extends WishlistState {
final WishlistModel wishlist;
const WishlistLoaded({this.wishlist = const WishlistModel()});
#override
List<Object> get props => [wishlist];
}
class WishlistError extends WishlistState {}
Here is my event:
part of 'wishlist_bloc.dart';
abstract class WishlistEvent extends Equatable {
const WishlistEvent();
#override
List<Object> get props => [];
}
class StartWishlist extends WishlistEvent {}
class AddWishlistProduct extends WishlistEvent {
final ProductModel product;
const AddWishlistProduct(this.product);
#override
List<Object> get props => [product];
}
class RemoveWishlistProduct extends WishlistEvent {
final ProductModel product;
const RemoveWishlistProduct(this.product);
#override
List<Object> get props => [product];
}
Here is my bloc:
import '../models/product_model.dart';
import '../models/wishlist_model.dart';
import 'package:flutter_bloc/flutter_bloc.dart';
import 'package:equatable/equatable.dart';
part 'wishlist_event.dart';
part 'wishlist_state.dart';
class WishlistBloc extends Bloc<WishlistEvent, WishlistState> {
WishlistBloc() : super(WishlistLoading()) {
on<StartWishlist>(_mapStartWishlistToState);
on<AddWishlistProduct>(_mapAddWishlistToState);
on<RemoveWishlistProduct>(_mapRemoveWishlistToState);
}
void _mapStartWishlistToState(event, emit) async {
emit(WishlistLoading());
try {
await Future.delayed(Duration(seconds: 1));
emit(WishlistLoaded());
} catch (_) {}
}
// Error ...
void _mapAddWishlistToState(event, emit) async {
if (state is WishlistLoaded) {
try {
emit(WishlistLoaded(
wishlist: WishlistModel(
products: List.from(state.wishlist.products)
..add(event.product))));
} catch (_) {}
}
}
void _mapRemoveWishlistToState(event, emit) async {}
}
But I get this error instead: "The getter 'wishlist' isn't defined for the type 'WishlistState'. Try importing the library that defines 'wishlist', correcting the name to the name of an existing getter, or defining a getter or field name 'wishlist'".
How to access 'wishlist' in the new version of flutter_bloc? Thank you.
Try to define arguments types while difining the functions. So your updated code would look like this:
import '../models/product_model.dart';
import '../models/wishlist_model.dart';
import 'package:flutter_bloc/flutter_bloc.dart';
import 'package:equatable/equatable.dart';
part 'wishlist_event.dart';
part 'wishlist_state.dart';
class WishlistBloc extends Bloc<WishlistEvent, WishlistState> {
WishlistBloc() : super(WishlistLoading()) {
on<StartWishlist>(_mapStartWishlistToState);
on<AddWishlistProduct>(_mapAddWishlistToState);
on<RemoveWishlistProduct>(_mapRemoveWishlistToState);
}
void _mapStartWishlistToState(
// Added argument types below
StartWishlist event, Emitter<WishlistState> emit) async {
emit(WishlistLoading());
try {
await Future.delayed(Duration(seconds: 1));
emit(WishlistLoaded());
} catch (_) {}
}
void _mapAddWishlistToState(
// Added argument types below
AddWishlistProduct event, Emitter<WishlistState> emit) async {
if (state is WishlistLoaded) {
try {
emit(WishlistLoaded(
wishlist: WishlistModel(
products: List.from(state.wishlist.products)
..add(event.product))));
} catch (_) {}
}
}
void _mapRemoveWishlistToState(
// Added argument types below
RemoveWishlistProduct event, Emitter<WishlistState> emit) async {}
}
Type promotion is impossible for properties, since they can potentially return different values each time they are called. As such, it is impossible for the compiler to know that the state getter will return a WishlistLoaded instance, even after knowing that the same getter returned a WishlistLoaded four lines earlier.
One way around this is to assign the state to a local variable, which is eligible for type promotion.
void _mapAddWishlistToState(AddWishlistProduct event, Emitter<WishlistState> emit) async {
final state = this.state; // local variable
if (state is WishlistLoaded) {
try {
emit(WishlistLoaded(
wishlist: WishlistModel(
products: List.from(state.wishlist.products)
..add(event.product))));
} catch (_) {}
}
}
The linked video used a parameter, which is also eligible for type promotion. If it had used the state getter directly in _mapAddWishlistProductToState, it would have run into the same error.
You just need to cast your state as following
void _mapAddWishlistToState(event, emit) async {
if (state is WishlistLoaded) {
try {
emit(WishlistLoaded(
wishlist: WishlistModel(
products: List.from((state as WishlistLoaded).wishlist.products)
..add(event.product))));
} catch (_) {}
}
}
Related
I am trying to fix an issue related to Flutter Bloc. I am editing someone else code to make it work with the latest flutter_bloc version but I am unable to do so. Can someone do a rewrite for my code so I can run it? I saw many answers but I am unable to understand how to fix my own code.
This is the complete code for all_categories_bloc.dart
class AllCategoriesBloc extends Bloc<AllCategoriesEvent, AllCategoriesState> {
AllCategoriesBloc({
this.apiRepository,
}) : super(AllCategoriesInitial()) {
on<GetAllCategories>(_onGetAllCategories);
}
final ApiRepository apiRepository;
Future<void> _onGetAllCategories(
GetAllCategories event,
Emitter<AllCategoriesState> emit,
) async {
try {
emit(const AllCategoriesLoading());
final categoriesModel = await apiRepository.fetchCategoriesList();
emit(AllCategoriesLoaded(categoriesModel));
if (categoriesModel.error != null) {
emit(AllCategoriesError(categoriesModel.error));
}
} catch (e) {
emit(
const AllCategoriesError(
"Failed to fetch all categories data. Is your device online ?",
),
);
}
}
}
Code for all_categories_event.dart
abstract class AllCategoriesEvent extends Equatable {
AllCategoriesEvent();
}
class GetAllCategories extends AllCategoriesEvent {
#override
List<Object> get props => null;
}
Code for all_categories_state.dart
abstract class AllCategoriesState extends Equatable {
const AllCategoriesState();
}
class AllCategoriesInitial extends AllCategoriesState {
AllCategoriesInitial();
#override
List<Object> get props => [];
}
class AllCategoriesLoading extends AllCategoriesState {
const AllCategoriesLoading();
#override
List<Object> get props => null;
}
class AllCategoriesLoaded extends AllCategoriesState {
final CategoriesModel categoriesModel;
const AllCategoriesLoaded(this.categoriesModel);
#override
List<Object> get props => [categoriesModel];
}
class AllCategoriesError extends AllCategoriesState {
final String message;
const AllCategoriesError(this.message);
#override
List<Object> get props => [message];
}
It throws an error "Bad state: add(GetAllCategories) was called without a registered event handler.
Make sure to register a handler via on((event, emit) {...})"
I have this add(GetAllCategories) in my home. dart file but the solution is to edit this code which I am unable to do so. Can someone do a rewrite for the latest bloc? I would be thankful.
Let's get through the migration guide step by step:
package:bloc v5.0.0: initialState has been removed. For more information check out #1304.
You should simply remove the AllCategoriesState get initialState => AllCategoriesInitial(); portion from your BLoC.
package:bloc v7.2.0 Introduce new on<Event> API. For more information, read the full proposal.
As a part of this migration, the mapEventToState method was removed, each event is registered in the constructor separately with the on<Event> API.
First of all, register your events in the constructor:
AllCategoriesBloc() : super(AllCategoriesInitial()) {
on<GetAllCategories>(_onGetAllCategories);
}
Then, create the _onGetAllCategories method:
Future<void> _onGetAllCategories(
GetAllCategories event,
Emitter<AllCategoriesState> emit,
) async {
try {
emit(const AllCategoriesLoading());
final categoriesModel = await _apiRepository.fetchCategoriesList();
emit(AllCategoriesLoaded(categoriesModel));
if (categoriesModel.error != null) {
emit(AllCategoriesError(categoriesModel.error));
}
} catch (e) {
emit(
const AllCategoriesError(
"Failed to fetch all categories data. Is your device online ?",
),
);
}
}
Notice, that instead of using generators and yielding the next state, you should use the Emitter<AllCategoriesState> emitter.
Here is the final result of the migrated AllCategoriesBloc:
class AllCategoriesBloc extends Bloc<AllCategoriesEvent, AllCategoriesState> {
AllCategoriesBloc() : super(AllCategoriesInitial()) {
on<GetAllCategories>(_onGetAllCategories);
}
final ApiRepository _apiRepository = ApiRepository();
Future<void> _onGetAllCategories(
GetAllCategories event,
Emitter<AllCategoriesState> emit,
) async {
try {
emit(const AllCategoriesLoading());
final categoriesModel = await _apiRepository.fetchCategoriesList();
emit(AllCategoriesLoaded(categoriesModel));
if (categoriesModel.error != null) {
emit(AllCategoriesError(categoriesModel.error));
}
} catch (e) {
emit(
const AllCategoriesError(
"Failed to fetch all categories data. Is your device online ?",
),
);
}
}
}
Bonus tip
Instead of creating an instance of ApiRepository inside the BLoC directly, you can use the constructor injection:
class AllCategoriesBloc extends Bloc<AllCategoriesEvent, AllCategoriesState> {
AllCategoriesBloc({
required this.apiRepository,
}) : super(AllCategoriesInitial()) {
on<GetAllCategories>(_onGetAllCategories);
}
final ApiRepository apiRepository;
...
}
Now, when creating BLoC, pass the instance of the repository to the constructor, like AllCategoriesBloc(apiRepository: ApiRepository()). This way you will be able to properly unit test your BLoC by mocking dependencies (in this case, ApiRepository).
since one cannot extend an extension of a class such as class MyBloc extends Bloc<MyEvent, MyState>, what is a cleanest way to get some functions out of my bloc file? Since the logic is a bit more complex, I would like to get some sub functions out like in
#override
Stream<MyState> mapEventToState(MyEvent event) async* {
yield* event.map(
loadRequested: (e) => _mapLoadRequestedToState(),
dataEntered: (e) => _mapDataEnteredToState(),
);
}
Stream<LogicChainState> _mapLoadRequestedToState() async* {
final dataRaw = loadData();
final dataProc = initData(dataRaw);
yield doSomeMore(dataProc);
}
I don't like the idea of using global functions. I could create a class
class MyBlocUtils {
MyData initData(MyData dataRaw) {
...
}
MyData doSomeMore(MyData dataProc) {
...
}
}
which still isn't as nice as using a function defined within the class MyBloc.
Any advice?
If all you want is to separate your methods into multiple files, but keep them in the same class, you could use extension methods.
my_bloc.dart
part 'my_bloc_utils.dart';
class MyBloc extends Bloc<MyEvent, MyState> {
Stream<LogicChainState> _mapLoadRequestedToState() async* {
final dataRaw = loadData();
final dataProc = initData(dataRaw);
yield doSomeMore(dataProc);
}
}
my_bloc_utils.dart
part of 'my_bloc.dart';
extension MyBlocUtils on MyBloc {
#override
Stream<MyState> mapEventToState(MyEvent event) async* {
yield* event.map(
loadRequested: (e) => _mapLoadRequestedToState(),
dataEntered: (e) => _mapDataEnteredToState(),
);
}
}
You can access the methods in just the same way as you keep everything in a single file:
import 'my_bloc.dart';
final myBloc = MyBloc();
final stream = myBloc.mapEventToState(MyEvent());
I am trying to find solution to manage async queries. For example, i have internet shop and i want to update all products and categories when city is changed. And i don't want to keep all async logic on ui. In order to achieve this result, i've created this bloc:
class AppEvent {
String message;
AppEvent({this.message = ''});
}
class EventsBlock extends Bloc<AppEvent, AppEvent> {
EventsBlock() : super(AppEvent());
#override
Stream<AppEvent> mapEventToState(AppEvent event) async* {
yield event;
}
}
final events = EventsBlock();
Then, i can use it like this:
class CityCubit() {
CityCubit() : super(CityState());
Future<void> changeCity() async {
await api.changeCity();
events.add(AppEvent(message: 'cityChanged'));
}
}
class CategoryCubit extends Cubit<CategoryState> {
CategoryCubit() : super(CategoryEmptyState()) {
events.stream.listen((e) {
if(e.message == 'cityChanged') {
fetchCategories();
}
});
};
Future<void> fetchCategories() async {
//fetch categories
}
}
class ProductCubit extends Cubit<ProductState> {
ProductCubit() : super(ProductEmptyState()) {
events.stream.listen((e) {
if(e.message == 'cityChanged') {
fetchProducts();
}
});
};
Future<void> fetchProducts() async {
//fetch products
}
}
It's something like eventBus pattern. But i am not sure that it's a correct way to use bloc. I've tried to use redux + redux saga, but it has a lot of boilerplate and i believe that flutter has better solution to manage things like that.
Your general idea is ok, but I can't see a real need for the EventsBloc class. In fact, it is kinda strange that you use the same class for the events and for the states of this bloc, and simply yield the event you receive. It's like EventsBloc could be a simple stream.
Here's a way to go, turning CityCubit into an actual bloc (and also with some error handling, which is something you can do gracefully with bloc):
abstract class CityState {}
class CityInitial extends CityState {}
class CityLoadingCities extends CityState {}
class CityCitiesLoaded extends CityState {}
class CityLoadError extends CityState {}
abstract class CityEvent {}
class CityLoadCities extends CityEvent {}
class CityBloc<CityEvent, CityState> {
CityBloc() : super(CityInitial());
#override
Stream<AppEvent> mapEventToState(CityEvent event) async* {
if(event is CityLoadCities) {
yield CityLoadingCities();
try {
await api.changeCity();
yield CityCitiesLoaded();
} catch (error) {
yield CityLoadError();
}
}
}
void changeCity() {
add(CityLoadCities());
}
}
Now you can do this inside any other bloc:
instanceOfCityBloc.listen((cityState) {
if(cityState is CityCitiesLoaded){
// do stuff
}
});
I ended up with this code:
class CityChangedEvent {
int cityId;
CityChangedEvent(this.cityId);
}
EventBus eventBus = EventBus();
mixin EventBusMixin {
StreamSubscription<T> listenEvent<T>(void Function(T) subscription) =>
eventBus.on<T>().listen(subscription);
void shareEvent<S>(S event) => eventBus.fire(event);
}
class CityCubit extends CityCubit<CityState> with EventBusMixin {
CityCubit() : super(CityInitialState());
Future<void> changeCity(cityId) async {
try {
emit(ChangeCityLoadingState());
final result = await api.changeCity(cityId);
if(result.success) {
emit(ChangeCitySuccessState());
shareEvent(CityChangedEvent(cityId));
}
} catch (_) {
emit(ChangeCityErrorState());
}
}
}
class CategoryCubit extends Cubit<CategoryState> with EventBusMixin {
CategoryCubit() : super(CategoryEmptyState()) {
listenEvent<CityChangedEvent>((e) {
fetchCategories(e.cityId);
);
}
Future<void> fetchCategories(cityId) async {
try {
emit(CategoryLoadingState());
final categoriesList = await fetchCategoriesApi();
emit(CategoryLoadedState(categories: categoriesList));
} catch (_) {
emit(CategoryErrorState());
}
}
}
Now, i can communicate between blocs without the need to instantiate or inject their instances. Thanks to this library https://pub.dev/packages/event_bus
I'm trying to figure out the BLoC library, but it gives me headaches.
I'm trying to fetch hotel names from an API. I have a model and a service responsible for contacting the API and fetching the data. However, I don't know how to connect it to the BLoC library.
Once my app starts, I want BLoC to fetch the data from the API and then show it in the app.
Here's my code:
hotel_model.dart
class Hotels {
final List<Hotel> hotels;
Hotels({this.hotels});
factory Hotels.fromJson(Map<String, dynamic> json) {
return Hotels(
hotels: List<Hotel>.from(
json['hotels'].map(
(x) => Hotel.fromJson(x),
),
),
);
}
}
class Hotel {
final String hotelName;
Hotel({this.hotelName});
factory Hotel.fromJson(Map<String, dynamic> json) {
return Hotel(
hotelName: json['name'],
);
}
}
hotel_service.dart
import 'package:http/http.dart' as http;
abstract class DownloadService {
Future<http.Response> fetchHotels();
}
class HotelService extends DownloadService {
#override
Future<http.Response> fetchHotels() {
final Uri uri = Uri.https('services.lastminute.com', 'mobile/stubs/hotels');
return http.get(uri);
}
}
And here's what I did wit the BLoC lib.
hotel_event.dart
part of 'hotel_bloc.dart';
#immutable
abstract class HotelEvent {}
class OnAppStartEvent extends HotelEvent {}
hotel_bloc.dart
import 'dart:async';
import 'package:bloc/bloc.dart';
import 'package:hotels/models/hotel/hotel_model.dart';
import 'package:hotels/services/hotel/hotel_service.dart';
import 'package:meta/meta.dart';
part 'hotel_event.dart';
part 'hotel_state.dart';
class HotelBloc extends Bloc<HotelEvent, HotelState> {
HotelBloc() : super(HotelFinal());
final HotelService hotelService = HotelService();
#override
Stream<HotelState> mapEventToState(
HotelEvent event,
) async* {
if (event is FetchEvent) {
final response = hotelService.fetchHotels();
yield
}
}
}
hotel_state.dart
part of 'hotel_bloc.dart';
#immutable
abstract class HotelState {
HotelState();
}
class HotelFinal extends HotelState {
final Hotel hotel;
HotelFinal(this.hotel);
Hotel getHotel() {
return hotel;
}
}
First of all add await to this line in your bloc
final response = await hotelService.fetchHotels();
return List<Hotel> from your fetchHotels function
you must have stateful class for your screen and in the initState
you can create your bloc object and call .add method on it
in your build method wrap your widget with BlocBuilder and on builder callback check your bloc state, if the state is HotelFinal return your ui with list of hotels in your state object.
It'll be useful to add another state for your HotelState for when your bloc is fetching the data, and even for when there's an error. e.g;
part of 'hotel_bloc.dart';
#immutable
abstract class HotelState {
HotelState();
}
class HotelFinal extends HotelState {
final Hotel hotel;
HotelFinal(this.hotel);
Hotel getHotel() {
return hotel;
}
}
class HotelLoading extends HotelState {
HotelLoading();
}
class HotelError extends HotelState {
final String error;
HotelError(this.error);
}
You would want to change your mapEventToState to something like this:
#override
Stream<HotelState> mapEventToState(
HotelEvent event,
) async* {
if (event is FetchEvent) {
yield HotelLoading();
try {
final response = await hotelService.fetchHotels();
// It seems like your service doesn't return an hotel directly, so you'll have to deal with this as it is not part of the question.
final hotel = getYourHotelHereWithTheResponse;
yield HotelFinal(hotel);
} catch (e) {
yield HotelError('something went wrong getting the hotel info');
}
}
}
Lastly, add a widget to your widget tree that adds FetchEvent to your bloc and add a BlocBuilder to react to the change of states. Note that this is very flexible and can be done in many ways, but it is out of the scope of your very broad question, I'm just showing you how to use the library at a minimal:
class MyStatefulWidget extends StatefulWidget {
#override
_MyStatefulWidgetState createState() => _MyStatefulWidgetState();
}
class _MyStatefulWidgetState extends State<MyStatefulWidget> {
HotelBloc hotelBloc;
#override
void initState() {
hotelBloc = HotelBloc..add(FetchEvent());
super.initState();
}
#override
void dispose() {
hotelBloc.close();
super.dispose();
}
#override
Widget build(BuildContext context) {
return BlocBuilder(builder: (context, state) {
if(state is HotelLoading) {
// return a widget to deal with loading
}
if(state is HotelFinal) {
// return a widget to deal with success
}
if(state is HotelError) {
// return a widget to deal with error
}
});
}
}
what is the correct approach to test riverpod with mockito?
running the code above,
/// ### edited snippets from production side ###
/// not important, skip to the TEST below!
/// this seems meaningless just because it is out of context
mixin FutureDelegate<T> {
Future<T> call();
}
/// delegate implementation
import '../../shared/delegate/future_delegate.dart';
const k_STRING_DELEGATE = StringDelegate();
class StringDelegate implements FutureDelegate<String> {
const StringDelegate();
#override
Future<String> call() async {
/// ... returns a string at some point, not important now
}
}
/// the future provider
import 'package:hooks_riverpod/hooks_riverpod.dart';
import '<somewhere>/delegate.dart'; /// the code above
final stringProvider = FutureProvider<String>((ref) => k_STRING_DELEGATE());
/// ### edited snippets from TEST side ###
/// mocking the delegate
import 'package:mockito/mockito.dart';
import '<see above>/future_delegate.dart';
class MockDelegate extends Mock implements FutureDelegate<String> {}
/// actual test
import 'package:flutter_test/flutter_test.dart';
import 'package:hooks_riverpod/all.dart';
import 'package:mockito/mockito.dart';
import '<somewhere in my project>/provider.dart';
import '../../domain/<somewhere>/mock_delegate.dart'; // <= the code above
void main() {
group('`stringProvider`', () {
final _delegate = MockDelegate();
test('WHEN `delegate` throws THEN `provider`return exception',
() async {
when(_delegate.call()).thenAnswer((_) async {
await Future.delayed(const Duration(seconds: 1));
throw 'ops';
});
final container = ProviderContainer(
overrides: [
stringProvider
.overrideWithProvider(FutureProvider((ref) => _delegate()))
],
);
expect(
container.read(stringProvider),
const AsyncValue<String>.loading(),
);
await Future<void>.value();
expect(container.read(stringProvider).data.value, [isA<Exception>()]);
});
});
}
running the test returns
NoSuchMethodError: The getter 'value' was called on null.
Receiver: null
Tried calling: value
dart:core Object.noSuchMethod
src/logic/path/provider_test.dart 28:48 main.<fn>.<fn>
I'm new to riverpod, clearly I'm missing something
I tried to follow this
I found that I had some extra errors specifically when using StateNotifierProvider. The trick was to not only override the StateNotifierProvider, but also its state property (which is a StateNotifierStateProvider object).
class SomeState {
final bool didTheThing;
SomeState({this.didTheThing = false});
}
class SomeStateNotifier extends StateNotifier<SomeState> {
SomeStateNotifier() : super(SomeState());
bool doSomething() {
state = SomeState(didTheThing: true);
return true;
}
}
final someStateProvider = StateNotifierProvider<SomeStateNotifier>((ref) {
return SomeStateNotifier();
});
class MockStateNotifier extends Mock implements SomeStateNotifier {}
void main() {
final mockStateNotifier = MockStateNotifier();
when(mockStateNotifier.doSomething()).thenReturn(true);
final dummyState = SomeState(didTheThing: true); // This could also be mocked
ProviderScope(
overrides: [
someStateProvider.overrideWithValue(mockStateProvider), // This covers usages like "useProvider(someStateProvider)"
someStateProvider.state.overrideWithValue(dummyState), // This covers usages like "useProvider(someStateProvider.state)"
],
child: MaterialApp(...),
);
}
There are 2 errors in your code
You're trying to test a throw error, so you should use thenThrow instead of thenAnswer, but because you're overriding a mixing method I would recommend instead of using Mock use Fake (from the same mockito library) to override methods and then throw it as you want
class MockDelegate extends Fake implements FutureDelegate<String> {
#override
Future<String> call() async {
throw NullThrownError; //now you can throw whatever you want
}
}
And the second problem (and the one your code is warning you) is that you deliberately are throwing, so you should expect an AsyncError instead, so calling container.read(stringProvider).data.value is an error because reading the riverpod documentation:
When calling data:
The current data, or null if in loading/error.
so if you're expecting an error (AsyncError) data is null, and because of that calling data.value its the same as writing null.value which is the error you're experiencing
This is the code you could try:
class MockDelegate extends Fake implements FutureDelegate<String> {
#override
Future<String> call() async {
throw NullThrownError;
}
}
void main() {
group('`stringProvider`', () {
final _delegate = MockDelegate();
test('WHEN `delegate` throws THEN `provider`return exception', () async {
final container = ProviderContainer(
overrides: [
stringProvider
.overrideWithProvider(FutureProvider((ref) => _delegate.call()))
],
);
expect(container.read(stringProvider), const AsyncValue<String>.loading());
container.read(stringProvider).data.value;
await Future<void>.value();
expect(container.read(stringProvider), isA<AsyncError>()); // you're expecting to be of type AsyncError because you're throwing
});
});
}
Also consider mocking out various providers by using an Override in your top level ProviderScope. That's what override can do quite well.