Rx.combineLatest2 not working as expected - google-app-engine

Question

I am a newbie in using flutter. I am try to create some sample application in flutter for create own application. I found a nice application in flutter with bloc pattern. please see the following link.
it's just a login page. there is a email and password textbox in the form with validation. One validator for email and another validator for the password length. There is a submit button in the form, initially it's disabled, if the email and password successfully validated then the submit button enabled. it uses the bloc pattern architecture with rxdart package.
I have a issue in submit button validation, after enter the email and password field it's not enabled the button field.
button validation code
Stream<bool> get submitCheck =>
Rx.combineLatest2(email, password, (e, p) => true);
Please see the below code.
main.dart
import 'package:bloc_login/pagetwo.dart';
import 'package:flutter/material.dart';
import 'package:bloc_login/bloc.dart';
import 'package:flutter/rendering.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
home: MyHomePage(title: 'Flutter Demo Home Page'),
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.teal,
),
debugShowCheckedModeBanner: false,
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
#override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
changethePage(BuildContext context) {
Navigator.of(context)
.push(MaterialPageRoute(builder: (context) => PageTwo()));
}
#override
Widget build(BuildContext context) {
final bloc = Bloc();
return Scaffold(
appBar: AppBar(
title: Text("Bloc pattern"),
),
body: SingleChildScrollView(
child: Container(
height: MediaQuery.of(context).size.height,
padding: EdgeInsets.all(16),
child: Column(
mainAxisSize: MainAxisSize.max,
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
StreamBuilder<String>(
stream: bloc.email,
builder: (context, snapshot) => TextField(
onChanged: bloc.emailChanged,
keyboardType: TextInputType.emailAddress,
decoration: InputDecoration(
border: OutlineInputBorder(),
hintText: "Enter Email",
labelText: "Email",
errorText: snapshot.error),
),
),
SizedBox(
height: 20,
),
StreamBuilder<String>(
stream: bloc.password,
builder: (context, snapshot) => TextField(
onChanged: bloc.passwordChanged,
keyboardType: TextInputType.text,
obscureText: true,
decoration: InputDecoration(
border: OutlineInputBorder(),
hintText: "Enter password",
labelText: "Password",
errorText: snapshot.error),
),
),
SizedBox(
height: 20,
),
StreamBuilder<bool>(
stream: bloc.submitCheck,
builder: (context, snapshot) => RaisedButton(
color: Colors.tealAccent,
onPressed: (snapshot.data != null)
? () => changethePage(context)
: null,
child: Text("Submit"),
))
],
),
),
),
);
}
}
bloc.dart
import 'dart:async';
import 'package:bloc_login/validator.dart';
import 'package:rxdart/rxdart.dart';
class Bloc extends Object with Validators implements BaseBloc {
final _emailController = StreamController<String>();
final _passwordController = StreamController<String>();
Function(String) get emailChanged => _emailController.sink.add;
Function(String) get passwordChanged => _passwordController.sink.add;
Stream<String> get email => _emailController.stream.transform(emailValidator);
Stream<String> get password =>
_passwordController.stream.transform(passwordValidator);
Stream<bool> get submitCheck =>
Rx.combineLatest2(email, password, (e, p) => true);
#override
void dispose() {
_emailController.close();
_passwordController.close();
}
}
abstract class BaseBloc {
void dispose();
}
validator.dart
import 'dart:async';
mixin Validators {
var emailValidator =
StreamTransformer<String, String>.fromHandlers(handleData: (email, sink) {
if (email.contains("#")) {
sink.add(email);
} else {
sink.addError("Email is not valid.");
}
});
var passwordValidator = StreamTransformer<String, String>.fromHandlers(
handleData: (password, sink) {
if (password.length > 4) {
sink.add(password);
} else {
sink.addError("Password length should be greater than 4.");
}
});
}
Please advice.

Answer 1

Combinelatest2 are fine, the problem is that you are creating a new bloc in each rebuild.
So create the bloc in the initState method and dispose the bloc in the dispose method of the StatefulWidget.
But also your StreamControllers have a Stream that supports only one single subscriber, so if you want that theStream of the StreamControllercan be listened to more than once, this need to be a broadcast stream, one of the ways to do it is using the StreamController .broadcast () constructor.
P.D. If you are creating forms with the bloc pattern you can check flutter_form_bloc, it saves you a lot of code.
Since dart 2.1 you don't need to extend an object to use a mixin
class Bloc with Validators implements BaseBloc {
final _emailController = StreamController<String>.broadcast();
final _passwordController = StreamController<String>.broadcast();
//...
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
#override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
Bloc _bloc;
#override
void initState() {
super.initState();
_bloc = Bloc();
}
#override
void dispose() {
_bloc.dispose();
super.dispose();
}
changethePage(BuildContext context) {
Navigator.of(context)
.push(MaterialPageRoute(builder: (context) => PageTwo()));
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text("Bloc pattern"),
),
body: SingleChildScrollView(
child: Container(
height: MediaQuery.of(context).size.height,
padding: EdgeInsets.all(16),
child: Column(
mainAxisSize: MainAxisSize.max,
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
StreamBuilder<String>(
stream: _bloc.email,
builder: (context, snapshot) => TextField(
onChanged: _bloc.emailChanged,
keyboardType: TextInputType.emailAddress,
decoration: InputDecoration(
border: OutlineInputBorder(),
hintText: "Enter Email",
labelText: "Email",
errorText: snapshot.error),
),
),
SizedBox(
height: 20,
),
StreamBuilder<String>(
stream: _bloc.password,
builder: (context, snapshot) => TextField(
onChanged: _bloc.passwordChanged,
keyboardType: TextInputType.text,
obscureText: true,
decoration: InputDecoration(
border: OutlineInputBorder(),
hintText: "Enter password",
labelText: "Password",
errorText: snapshot.error),
),
),
SizedBox(
height: 20,
),
StreamBuilder<bool>(
stream: _bloc.submitCheck,
builder: (context, snapshot) => RaisedButton(
color: Colors.tealAccent,
onPressed: (snapshot.data != null)
? () => changethePage(context)
: null,
child: Text("Submit"),
))
],
),
),
),
);
}
}