the current state in mapEventToState in Flutter Bloc is not yield - android-studio

Question

I am trying to make a simple app for testing the BloC pattern but, there's a change in the current version of the BloC Pattern, that the "Current State" now not sending with the mapEventToState method as a parameter but according to the online document you can replace it with only "state", but it not working with me,
and this is my code:
class CounterBloc extends Bloc<CounterEvent, CounterState> {
void onIncrement(){
add(IncrementEvent());
}
void onDecrement() {
add(DecrementEvent());
}
#override
// TODO: implement initialState
CounterState get initialState => CounterState.initial();
#override
Stream<CounterState> mapEventToState(CounterEvent event) async* {
if (event is IncrementEvent) {
yield state..counter += 1;
} else if (event is DecrementEvent) {
yield state..counter -= 1;
}
}
}
and this is the Counter state class
class CounterState {
int counter;
CounterState._();
factory CounterState.initial() {
return CounterState._()..counter = 0;
}
}
and this is my main app dart file
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
#override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
#override
Widget build(BuildContext context) {
return BlocProvider(
create: (context) => CounterBloc(),
child: CounterWidget(widget: widget),
);
}
}
class CounterWidget extends StatelessWidget {
final MyHomePage widget;
const CounterWidget({Key key, #required this.widget}) :super (key: key);
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: BlocBuilder(
bloc: BlocProvider.of<CounterBloc>(context),
builder: (context, CounterState state) {
return Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text(
'You have pushed the button this many times:',
),
Text(
'${state.counter}',
style: Theme.of(context).textTheme.display1,
),
],
),
);
},
),
floatingActionButton: Row(
mainAxisAlignment: MainAxisAlignment.end,
children: <Widget>[
FloatingActionButton(
onPressed: () => BlocProvider.of<CounterBloc>(context).onIncrement(),
tooltip: 'Increment',
child: Icon(Icons.add),
),
SizedBox(width: 10,),
FloatingActionButton(
onPressed: () => BlocProvider.of<CounterBloc>(context).onDecrement(),
tooltip: 'Decrement',
child: Icon(Icons.remove),
),
],
)
);
}
}
please can anyone help me with this issue?

Answer 1

You can copy paste run full code below
Step 1 : add CounterState({this.counter}); in CounterState
Step 2 : yield state..counter += 1; will not cause Widget build , please change to yield CounterState(counter: state.counter + 1);
working demo
full code
import 'package:flutter/material.dart';
import 'package:bloc/bloc.dart';
import 'package:flutter_bloc/flutter_bloc.dart';
abstract class CounterEvent {}
class IncrementEvent extends CounterEvent {}
class DecrementEvent extends CounterEvent {}
void main() => runApp(MyApp());
class CounterState {
int counter;
CounterState._();
CounterState({this.counter}); //add this line
factory CounterState.initial() {
return CounterState._()..counter = 0;
}
}
class CounterBloc extends Bloc<CounterEvent, CounterState> {
void onIncrement() {
add(IncrementEvent());
}
void onDecrement() {
add(DecrementEvent());
}
#override
// TODO: implement initialState
CounterState get initialState => CounterState.initial();
#override
Stream<CounterState> mapEventToState(CounterEvent event) async* {
if (event is IncrementEvent) {
//yield state..counter += 1;
yield CounterState(counter: state.counter + 1);
} else if (event is DecrementEvent) {
//yield state..counter -= 1;
yield CounterState(counter: state.counter - 1);
}
}
}
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
#override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
#override
Widget build(BuildContext context) {
return BlocProvider(
create: (context) => CounterBloc(),
child: CounterWidget(widget: widget),
);
}
}
class CounterWidget extends StatelessWidget {
final MyHomePage widget;
const CounterWidget({Key key, #required this.widget}) : super(key: key);
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: BlocBuilder(
bloc: BlocProvider.of<CounterBloc>(context),
builder: (context, CounterState state) {
return Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text(
'You have pushed the button this many times:',
),
Text(
'${state.counter}',
style: Theme.of(context).textTheme.display1,
),
],
),
);
},
),
floatingActionButton: Row(
mainAxisAlignment: MainAxisAlignment.end,
children: <Widget>[
FloatingActionButton(
onPressed: () =>
BlocProvider.of<CounterBloc>(context).onIncrement(),
tooltip: 'Increment',
child: Icon(Icons.add),
),
SizedBox(
width: 10,
),
FloatingActionButton(
onPressed: () =>
BlocProvider.of<CounterBloc>(context).onDecrement(),
tooltip: 'Decrement',
child: Icon(Icons.remove),
),
],
));
}
}