Flutter BLoC, Scoped Instances

Flutter BLoC, inheritedWidget Provider

main.dart

import 'package:flutter/material.dart';
import 'src/app.dart';

void main() => runApp(App());

src/app.dart

import 'package:flutter/material.dart';
import 'screens/login_screen.dart';
import 'blocs/provider.dart';

class App extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Provider(
      child: MaterialApp(
        title: 'Login',
        home: Scaffold(
          appBar: AppBar(
            title: Text('LoginForm'),
          ),
          body: LoginScreen(),
        ),
      ),
    );
  }
}

src/screens/login_screen.dart

import 'package:flutter/material.dart';
import '../blocs/bloc.dart';
import '../blocs/provider.dart'; // Different Code of "Single Global Instance"

class LoginScreen extends StatefulWidget {
  @override
  _LoginScreenState createState() => _LoginScreenState();
}

class _LoginScreenState extends State<LoginScreen> {
  @override
  Widget build(BuildContext context) {
    final bloc = Provider.of(context); // Different Code of "Single Global Instance"

    return Container(
      margin: EdgeInsets.all(8.0),
      child: Form(child: 
        Column(children: <Widget>[
          fieldEmail(bloc), // Different Code of "Single Global Instance"
          fieldPassword(bloc), // Different Code of "Single Global Instance"
          _submit(),
          ],
        ),
      ),
    );
  }

  Widget fieldEmail(Bloc bloc) { // Different Code of "Single Global Instance"
    return StreamBuilder(
      stream: bloc.email,
      builder: (context, snapshot) {
        return TextField(
          onChanged: bloc.changeEmail,
          keyboardType: TextInputType.emailAddress,
          decoration: InputDecoration(
            labelText: 'Email',
            hintText: 'useanem@domain.com',
            errorText: snapshot.error,
          ),
        );
      }
    );
  }

  Widget fieldPassword(Bloc bloc) { // Different Code of "Single Global Instance"
    return StreamBuilder(
      stream: bloc.password,
      builder: (context, snapshot) {
        return TextField(
          onChanged: bloc.changePassword,
          obscureText: true,
          decoration: InputDecoration(
            labelText: 'Password',
            hintText: 'over 3 charactor',
            errorText: snapshot.error,
          ),
        );
      }
    );
  }

  Widget _submit() {
    return RaisedButton(
      color: Colors.blue,
      child: Text('Submit', style: TextStyle(color: Colors.white),),
      onPressed: (){
        print('onPressed Submit');
      },
    );
  }
}

src/blocs/bloc.dart

import 'dart:async';
import 'validators.dart';

class Bloc extends Object with Validators {
  final _email = StreamController<String>();
  final _passwd = StreamController<String>();

  Stream<String> get email => _email.stream.transform(validatorEmail);
  Stream<String> get password => _passwd.stream.transform(validatorPassword);

  Function(String) get changeEmail => _email.sink.add;
  Function(String) get changePassword => _passwd.sink.add;

  dispose() {
    _email.close();
    _passwd.close();
  }
}

// Different Code of "Single Global Instance"
// final bloc = Bloc();

src/blocs/provider.dart

import 'package:flutter/material.dart';
import 'bloc.dart';

class Provider extends InheritedWidget {
  final bloc = Bloc();

  Provider({key, Widget child}) : super(key: key, child: child);

  // @override
  // bool updateShuldNotify(_) => true;
  @override
  bool updateShouldNotify(InheritedWidget oldWidget) => true;
  /*{
    // TODO: implement updateShouldNotify
    throw UnimplementedError();
  }*/

  static Bloc of(BuildContext context) {
    // ignore: deprecated_member_use
    // return (context.inheritFromWidgetOfExactType(Provider) as Provider).bloc;
    // https://stackoverflow.com/a/59304297
    return (context.dependOnInheritedWidgetOfExactType<Provider>()).bloc;
  }
}

src/blocs/validators.dart

import 'dart:async';

class Validators {
  final validatorEmail = StreamTransformer<String, String>.fromHandlers(
    handleData: (String email, sink) {
      if( email.contains('@') ){
        sink.add(email);
      } else {
        sink.addError('Enter a valid email');
      }
    }
  );

  final validatorPassword = StreamTransformer<String, String>.fromHandlers(
    handleData: (String passwd, sink) {
      if( passwd.length >= 3 ) {
        sink.add(passwd);
      } else {
        sink.addError('password must be at leat 3 characters');
      }
    }
  );
}

Flutter State

• Flutter BLoC
• Flutter BLoC, Single Global Instance
• Flutter BLoC, Scoped Instances
• Flutter BLoC, RxDart combineLatestStream
• Flutter BLoC, RxDart combineLatestStream BehaviorSubject On Submit