using Provider for Authentication in Flutter

login_model.dart

import 'dart:convert';

import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:meler/repositories/user.repository.dart';

class LoginModel with ChangeNotifier {
  TextEditingController _emailCtrl = TextEditingController();
  TextEditingController _passwordCtrl = TextEditingController();
  bool _isLoading = false;
  String _errorMessage = "";

  // Getters
  TextEditingController get emailCtrl => _emailCtrl;
  TextEditingController get passwordCtrl => _passwordCtrl;
  bool get isLoading => _isLoading;
  String get errorMessage => _errorMessage;

  UserRepository _userRepository = UserRepository();
  PersistData _localStorageService = PersistData();

  pageIsLoading(bool isLoadn) {
    _isLoading = isLoadn;
    notifyListeners();
  }

  Future<bool> signIn(String email, String password) async {
    // Validate
    if (!isValidForm(email, password)) {
      return false;
    }

    bool successful = false;
    pageIsLoading(true);
    await _userRepository.login(email, password).then((response){
      pageIsLoading(false);
      int statusCode = response.statusCode;
      var body = json.decode(response.body);

      if (statusCode != 200) {
        _setErrorMessage("Sorry an error occured!");
        successful = false;
      } else {
        successful = true;

        // Set Token
        _localStorageService.setLoginToken(body["access_token"]);
        _localStorageService.setLoggedInUser(body["user"]);
      }
    });
    

    return successful;
  }



  //? Validations
  bool isValidForm(String email, String password) {
    // Email
    if (email.isEmpty) {
      _setErrorMessage("Email field is required");
      return false;
    } else if (!email.contains('@')) {
      _setErrorMessage("Please enter a valid email");
      return false;
    } else if (password.isEmpty) {
      _setErrorMessage("Password field is required");
      return false;
    } else {
      return true;
    }
  }

  void _setErrorMessage(String msg) {
    _errorMessage = msg;
    notifyListeners();
  }
}

login_page.dart

import 'package:flutter/material.dart';

class LoginPage extends StatelessWidget {
    final model = Provider.of<LoginModel>(context);
  
  @override
  Widget build(BuildContext context) {
    return Scaffold(
       appBar: AppBar(
        title: Text('Profile'),
      ),
      body: FlatButton(
        child:Text('login'),
      onPressed: () async{
        bool isSuccess = await model.signIn(model.email.text, model.password.text);
      }
      )
    );
  }
}

main.dart

import 'package:flutter/material.dart';
import 'package:dummy/view_models/login_model.dart';
import 'package:provider/provider.dart';

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

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

class App extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MultiProvider(
      providers: [
        ChangeNotifierProvider<LoginModel>.value(value: LoginModel()),
      ],
      child: MaterialApp(
        title: 'Dummy app',
        initialRoute: HomePage(),
      ),
    );
  }
}

user_repository.dart

import 'dart:convert';

import 'package:http/http.dart' as http;
import 'package:dummy/services/constants.dart';
import 'package:dummy/utils/api.dart';

class UserRepository {

//login method
  Future<http.Response> login(String email, String password) async {
    final body = jsonEncode({"email": email, "password": password});
    http.Response response = await http.post(Api.loginApi, body: body, headers: Api.httpHeaders);
    print(response.body);
    return response;
  }

}