Using Stream/Sink in Flutter - dart

Question

I'm trying to replace the increment flutter app code, by using Streams from Dart API without using scoped_model or rxdart.
So I read this and watched this, but could not get it work for me, my codes are:
StreamProvider.dart:
import 'package:flutter/widgets.dart';
import 'businessLogic.dart';
import 'dart:async';
class Something {
final _additionalContrllerr = StreamController<int>();
Sink<int> get addition => _additionalContrllerr.sink;
Stream<int> get itemCount => _additionalContrllerr.stream;
}
class StreemProvider extends InheritedWidget {
final Something myBloc; // Business Logic Component
StreemProvider({
Key key,
#required this.myBloc,
Widget child,
}) : super(key: key, child: child);
#override
bool updateShouldNotify(InheritedWidget oldWidget) => true;
static Something of(BuildContext context) =>
(context.inheritFromWidgetOfExactType(StreemProvider) as StreemProvider)
.myBloc;
}
main.dart:
import 'package:flutter/material.dart';
import 'package:flutter_app/StreemProvider.dart';
void main() => runApp(MyApp(
textInput: Text("Provided By the Main"),
));
class MyApp extends StatefulWidget {
final Widget textInput;
MyApp({this.textInput});
#override
State<StatefulWidget> createState() => MyAppState();
}
class MyAppState extends State<MyApp> {
bool checkBoxValue = false;
int _counter = 0;
#override
Widget build(BuildContext ctxt) {
var x = Something(); //// Not sure if have to use this!
return StreemProvider(
myBloc: x, //// Not sure about this!!
child: MaterialApp(
home: SafeArea(
child: Scaffold(
body: new Center(
child: new Column(
children: <Widget>[
widget.textInput,
Text("clickec $_counter times"),
Text("clickec ${x.itemCount.listen((int i) => i)} times"),
/// How to get the value of i??!
Checkbox(
value: checkBoxValue,
onChanged: (bool newValue){
setState(() {
checkBoxValue = newValue;
});
}
)
],
)),
floatingActionButton: Incrementer(_increment),
// floatingActionButton: Incrementer(x),
),
),
),
);
}
_increment() {
setState(() {
_counter += 1;
});
}
}
class Incrementer extends StatefulWidget {
final Function increment;
Incrementer(this.increment);
#override
State<StatefulWidget> createState() {
return IncrementerState();
}
}
class IncrementerState extends State<Incrementer>{
#override
Widget build(BuildContext ctxt) {
final myBloc = StreemProvider.of(context);
return new FloatingActionButton(
//onPressed: widget.increment,
// How ot get the latest value!!
onPressed: () async {
var y = await myBloc.itemCount.last;
if (y.isNaN) y = 0;
myBloc.addition.add(y+1);
},
child: new Icon(Icons.add),
);
}
}

Answer 1

don't know the restrictions on rx_dart, but I can only try to answer by you using it. lol
your bloc doesnt define wht to listen in your input stream, this is how I could get it to work
counter_bloc.dart
import 'package:rxdart/rxdart.dart';
import 'dart:async';
class CounterBloc {
int _count = 0;
ReplaySubject<int> _increment = ReplaySubject<int>();
Sink<int> get increment => _increment;
BehaviorSubject<int> _countStream = BehaviorSubject<int>(seedValue: 0);
Stream<int> get count => _countStream.stream;
CounterBloc() {
_increment.listen((increment) {
_count += increment;
_countStream.add(_count);
});
}
}
In the constructor the listen method is set for that stream. for each increment sent, it'll increment the counter and send the current count to another stream.
In main.dart, removed the _counter property since that's now being handled by the BLOC. and to display I used a stream builder.
also added a second fab, with a +2 increment to test the logic.
hope this helps you model your bloc class. :)
a good bloc reference: https://www.youtube.com/watch?v=PLHln7wHgPE
main.dart
import 'counter_bloc.dart';
import 'package:flutter/material.dart';
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> {
CounterBloc bloc = CounterBloc();
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text(
'You have pushed the button this many times:',
),
StreamBuilder<int>(
stream: bloc.count,
initialData: 0,
builder: (BuildContext c, AsyncSnapshot<int> data) {
return Text(
'${data.data}',
style: Theme.of(context).textTheme.display1,
);
},
),
],
),
),
floatingActionButton: Row(
mainAxisAlignment: MainAxisAlignment.end,
children: <Widget>[
FloatingActionButton(
onPressed: () {
bloc.increment.add(2);
},
tooltip: 'Increment 2',
child: Text("+2"),
),
FloatingActionButton(
onPressed: () {
bloc.increment.add(1);
},
tooltip: 'Increment 1',
child: Text("+1"),
),
],
), // This trailing comma makes auto-formatting nicer for build methods.
);
}
}

Answer 2

Thanks a lot to vbandrade his answer helped me figuring t out. the solution worked with me is:
I need to have 2 StreamController if I need to listen to a sink in my bloc Business Logic Component, then process and stream the output to other elements.
The counter_bloc.dart is:
import 'dart:async';
class CounterBloc {
int _count = 0;
// The controller to stream the final output to the required StreamBuilder
final _counter = StreamController.broadcast<int>();
Stream<int> get counter => _counter.stream;
// The controller to receive the input form the app elements
final _query = StreamController<int>();
Sink<int> get query => _query.sink;
Stream<int> get result => _query.stream;
// The business logic
CounterBloc() {
result.listen((increment) { // Listen for incoming input
_count += increment; // Process the required data
_counter.add(_count); // Stream the required output
});
}
void dispose(){
_query.close();
_counter.close();
}
}
And the main.dart is:
import 'counter_bloc.dart';
import 'package:flutter/material.dart';
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
State<StatefulWidget> createState() {
return _MyHomePageState();
}
}
class _MyHomePageState extends State<MyHomePage> {
var bloc = CounterBloc();
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text(
'You have pushed the button this many times:',
),
StreamBuilder<int>( // Listen to the final output sent from the Bloc
stream: bloc.counter,
initialData: 0,
builder: (BuildContext c, AsyncSnapshot<int> data) {
return Text(
'${data.data}',
style: Theme.of(context).textTheme.display1,
);
},
),
],
),
),
floatingActionButton: Row(
mainAxisAlignment: MainAxisAlignment.end,
children: <Widget>[
FloatingActionButton(
onPressed: () {
bloc.query.add(2); // Send input to the Bloc
},
tooltip: 'Increment 2',
child: Text("+2"),
),
FloatingActionButton(
onPressed: () {
bloc.query.add(1); // Send input to the Bloc
},
tooltip: 'Increment 1',
child: Text("+1"),
),
],
), // This trailing comma makes auto-formatting nicer for build methods.
);
}
}

Answer 3

A simple implementation
import 'dart:async';
import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Counter Demo',
debugShowCheckedModeBanner: false,
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: MyHomePage(),
);
}
}
class MyHomePage extends StatelessWidget {
int _counter = 0;
final StreamController<int> _streamController =
StreamController<int>.broadcast();
Stream<int> get _stream => _streamController.stream;
void incrementCounter() {
_counter++;
_streamController.add(_counter);
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('Flutter demo'),
),
body: Center(
child: StreamBuilder<int>(
stream: _stream,
builder: (ctxt, snapshot) {
if (snapshot.hasData) {
return Text(
'You have pushed this button ${snapshot.data} times');
}
return Text('You have pushed this button ${0} times');
}),
),
floatingActionButton: FloatingActionButton(
onPressed: () {
incrementCounter();
},
tooltip: 'Increment',
child: Icon(Icons.add),
),
);
}
}