Flutter Bloc Builder не вызывается и не обновляет пользовательский интерфейс после изменения состояния
У меня проблема с пакетом Flutter Bloc. Основная идея - получить список пользователей из API, я отключился от Интернета, чтобы посмотреть, как работает мое состояние ошибки, но когда блок try / catch вылавливает ошибку, мой Bloc Builder не восстанавливается, и мой пользовательский интерфейс не меняется, а у меня выполнить горячий перезапуск, чтобы увидеть результаты.
UserBloc класс:
import 'dart:io';
import 'package:chopper/chopper.dart';
import 'package:flutter/material.dart';
import 'package:flutter_bloc/flutter_bloc.dart';
import 'package:listviewblocflutter/bloc/user/user_event.dart';
import 'package:listviewblocflutter/bloc/user/user_state.dart';
import 'package:listviewblocflutter/data/error/network_error.dart';
import 'package:listviewblocflutter/data/service/user_service.dart';
import 'package:listviewblocflutter/model/built/built_user.dart';
import 'package:built_collection/built_collection.dart';
class UserBloc extends Bloc<UserEvent, UserState> {
UserService _userService;
UserBloc() {
this._userService = UserService.create();
}
@override
UserState get initialState => UserInitial();
@override
Stream<UserState> mapEventToState(UserEvent event) async* {
yield UserLoading();
if (event is GetAllUsers) {
print("getallusers");
try {
final listOfUsers = await _userService.getAllUsers();
yield UsersLoaded(listOfUsers.body);
print("users loaded (userBloc)");
} catch (_) {
print("got an error (userBloc)");
yield UserLoadingError("Can't get all users!");
}
} else if (event is GetUserById) {
// single user event
}
}
}
UserEvent класс:
import 'package:equatable/equatable.dart';
abstract class UserEvent extends Equatable {
const UserEvent();
}
class GetAllUsers extends UserEvent {
const GetAllUsers();
@override
List<Object> get props => [];
}
class GetUserById extends UserEvent {
final int id;
const GetUserById(this.id);
@override
List<Object> get props => [id];
}
UserState класс:
import 'package:equatable/equatable.dart';
import 'package:flutter/cupertino.dart';
import 'package:listviewblocflutter/model/built/built_user.dart';
import 'package:built_collection/built_collection.dart';
@immutable
abstract class UserState extends Equatable {
const UserState();
}
class UserInitial extends UserState {
const UserInitial();
@override
List<Object> get props => [];
}
class UserLoading extends UserState {
const UserLoading();
@override
List<Object> get props => [];
}
class UserLoaded extends UserState {
final BuiltUser user;
const UserLoaded(this.user);
@override
List<Object> get props => [user];
}
class UsersLoaded extends UserState {
final BuiltList<BuiltUser> listOfUsers;
const UsersLoaded(this.listOfUsers);
@override
List<Object> get props => [listOfUsers];
}
class UserLoadingError extends UserState {
final String message;
const UserLoadingError(this.message);
@override
List<Object> get props => [message];
}
class UserEmpty extends UserState {
const UserEmpty();
@override
List<Object> get props => [];
}
Я завернул свою домашнюю страницу с помощью BlocProvider в файл main.dart, чтобы получить доступ к моему UserBloc в HomePage:
class MyApp extends StatelessWidget {
// This widget is the root of your application.
@override
Widget build(BuildContext context) {
return MaterialApp(
debugShowCheckedModeBanner: false,
title: 'ListView with BLoC pattern',
home: SafeArea(
child: Scaffold(
body: BlocProvider(
create: (context) => UserBloc(), child: HomePage()))),
);
}
}
Пытался сделать мой класс HomePage как StateLessWidget, но проблема все еще возникла, прямо сейчас мой класс StateFulWidget с той же проблемой. Я получаю AllUsers в методе initState:
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:flutter_bloc/flutter_bloc.dart';
import 'package:listviewblocflutter/bloc/bloc.dart';
import 'package:listviewblocflutter/model/built/built_user.dart';
import 'package:built_collection/built_collection.dart';
class HomePage extends StatefulWidget {
@override
_HomePageState createState() => _HomePageState();
}
class _HomePageState extends State<HomePage> {
@override
void initState() {
BlocProvider.of<UserBloc>(context).add(GetAllUsers());
super.initState();
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text("Users"),
),
body: Container(
child: BlocListener<UserBloc, UserState>(
listener: (context, state) {
if (state is UserLoadingError) {
print("showing snackbar (listener)");
_showNetworkErrorSnackbar(context, state.message);
}
},
child: BlocBuilder<UserBloc, UserState>(
builder: (context, state) {
print("bloc builder");
if (state is UserLoading || state is UserInitial)
return _showLoadingStatus();
else if (state is UsersLoaded)
return _buildList(state.listOfUsers);
else if (state is UserEmpty || state is UserLoadingError) {
print("state is empty/error (builder)");
return _emptyListLayout();
}
return Center();
},
),
),
),
);
}
ListView _buildList(BuiltList<BuiltUser> listOfUsers) {
return ListView.builder(
itemCount: listOfUsers.length,
itemBuilder: (context, index) {
return Card(
child: ListTile(
leading: CircleAvatar(
backgroundColor: Colors.redAccent,
),
title: Padding(
padding: EdgeInsets.only(left: 10),
child: Text(
listOfUsers[index].username,
overflow: TextOverflow.ellipsis,
),
),
),
);
});
}
Widget _showLoadingStatus() {
return Center(
child: CircularProgressIndicator(),
);
}
Widget _emptyListLayout() {
return Center(
child: Text(
"List is empty ;(",
textAlign: TextAlign.center,
),
);
}
void _showNetworkErrorSnackbar(BuildContext context, String message) {
Scaffold.of(context).showSnackBar(SnackBar(
content: Text(message),
));
}
}
My goal is to tell the user that list is empty and show a snackbar when UserLoadingError state appears, but I only see a stuck LoadingIndicator
My "print" debugger in logs says:
I/flutter (14034): bloc builder
I/flutter (14034): getallusers
I/flutter (14034): bloc builder
I/flutter (14034): got an error (userBloc)
I/flutter (14034): showing snackbar (listener)
Expected results:
I/flutter (14034): bloc builder
I/flutter (14034): getallusers
I/flutter (14034): bloc builder
I/flutter (14034): got an error (userBloc)
I/flutter (14034): showing snackbar (listener) /// a snackbar should appear after this message
I/flutter (14034): bloc builder
I/flutter (14034): state is empty/error (builder) /// an empty list layout should be created after this message
pubspecs.yaml fragment:
dependencies:
flutter:
sdk: flutter
cupertino_icons: ^0.1.3
chopper: ^3.0.2
equatable: ^1.1.1
flutter_bloc: ^4.0.0
provider: ^4.1.1
built_value: ^7.1.0
dev_dependencies:
chopper_generator: ^3.0.4
build_runner: ^1.10.0
built_value_generator: ^7.1.0
flutter_test:
sdk: flutter
I could upload my UserService class where I get users from API using Chopper, let me know if it's needed.
1 ответ
Наконец-то я обнаружил проблему. Проблема была в моем дереве BlockBuilder if/else, точнее:
if (state is UserLoading || state is UserInitial)
return _showLoadingStatus();
я изменился на:
if (state is UserLoading)
return _showLoadingStatus();
И вот проблема исчезла.