Version: 9.0.7

Inmutable States

Meedu is designed to streamline state management for both simple and complex apps, emphasizing the use of immutable state.

note

An immutable state is an instance of one Class that overrides == and hashCode. For example you could use equatable or freezed to create an immutable Class.

With equatable#

Add equatable as a dependency in your pubspec.yaml file

equatable: latest_version

Now you can create a Class to manage your state

import 'package:equatable/equatable.dart';

class LoginState extends Equatable {
  final String email, password;
  LoginState({
    required this.email,
    required this.password,
  });

  LoginState copyWith({
    String? email,
    String? password,
  }) {
    return LoginState(
      email: email ?? this.email,
      password: password ?? this.password,
    );
  }

  @override
  List<Object?> get props => [email, password];
}

With freezed#

To use freezed you need build_runner and freezed_annotation

in your pubspec.yaml file (replace latest_version with the latest version of each dependency)

dependencies:
  flutter:
    sdk: flutter
  freezed_annotation: latest_version

dev_dependencies:
  flutter_test:
    sdk: flutter

  build_runner: latest_version
  freezed: latest_version

import 'package:freezed_annotation/freezed_annotation.dart';
part 'login_state.freezed.dart';
@freezed
class LoginState with _$LoginState {
  const LoginState._();
  const factory LoginState({
    required String email,
    required String password,
  }) = _LoginState;
}

Now you can use the LoginState class to create a StateNotifier

import 'package:flutter_meedu/notifiers.dart';

class LoginNotifier extends StateNotifier<LoginState> {
  // you need pass an inital state using super
  LoginNotifie(super.initialState);

  void onEmailChanged(String email) {
    state = state.copyWith(email: email);
  }

  void onPasswordChanged(String password) {
    state = state.copyWith(password: password);
  }
}

info

If you only want to update the state of your StateNotifier but you don't want to notify to the listeners (don't rebuild the Consumer widgets) you can use the onlyUpdate method in your StateNotifier.

class LoginNotifier extends StateNotifier<LoginState> {
  LoginNotifie(super.initialState);

  void onEmailChanged(String email) {
    // only update the state
    onlyUpdate(state.copyWith(email: email));
  }
  .
  .
  .

}

Next you need to create a StateNotifierProvider and use the Consumer widget to listen the changes in your state

Consider the following Login Form UI, where the ElevatedButton is enabled only when both the email and password in our state are not empty.

import 'package:flutter/material.dart';
import 'package:flutter_meedu/providers.dart';
import 'package:flutter_meedu/consumer.dart';


final loginProvider = Provider.state<LoginNotifier, LoginState>(
  (_) => LoginController(
    LoginState(
      email: '',
      password:'',
    ),
  ),
);


class LoginView extends StatelessWidget {
  const LoginView({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: SafeArea(
        child: Padding(
          padding: const EdgeInsets.all(8.0),
          child: Column(
            children: [
              TextField(
                onChanged: loginProvider.read().onEmailChanged,
                decoration: InputDecoration(
                  labelText: "Email",
                ),
              ),
              TextField(
                onChanged: loginProvider.read().onPasswordChanged,
                decoration: InputDecoration(
                  labelText: "Password",
                ),
              ),
              SizedBox(height: 30),
              Consumer(
                builder: (_, ref, __) {
                  final notifier = ref.watch(loginProvider);
                  final state = notifier.state;

                  final email = state.email;
                  final password = state.password;

                  final enabled = email.isNotEmpty && password.isNotEmpty;

                  return ElevatedButton(
                    onPressed: enabled
                        ? () {
                            // YOUR CODE HERE
                          }
                        : null,
                    child: Text("SEND"),
                  );
                },
              )
            ],
          ),
        ),
      ),
    );
  }
}

ConsumerWidget#

Also you can extend from ConsumerWidget to create a widget and listen the changes in your notifier

import 'package:flutter/material.dart';
import 'package:flutter_meedu/consumer.dart';

class CounterView extends ConsumerWidget {
  @override
  Widget build(BuildContext context, ref) {
    final controller = ref.watch(counterProvider);
    return Text("${controller.counter}");
  }
}

class CounterPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(),
      body: Center(
        child: CounterView(),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          counterProvider.read.increment();
        },
      ),
    );
  }
}

NOTE

The ref parameter in a Consumer or a ConsumerWidget can be used to listen multiples providers.

class CounterView extends ConsumerWidget {
  @override
  Widget build(BuildContext context, ref) {
    final counterNotifier = ref.watch(counterProvider);
    final loginNotifier = ref.watch(loginProvider);
    return Text("${counterNotifier.state} ${loginNotifier.state.email}");
  }
}

Listen to changes in our notifiers without rebuilding the UI#

Sometimes we need to listen the changes in our state and perform some actions like showing a dialog, snackback, or navigation. In those cases, you can use ref.listen inside a Consumer or a ConsumerWidget.

class CounterView extends ConsumerWidget {
  @override
  Widget build(BuildContext context, ref) {

    ref.listen(
      loginProvider,
      callback: (notifier) {
        // YOUR ACTION HERE
      },
    );
   
    return MY_WIDGET;
  }
}

note

ref.listen only listens the changes in our state but does not rebuild our Consumer or ConsumerWidget.