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How I use Amplify Auth with Flutter

Offline Programmer
Full Stack Architect | Problem Solver | Lifelong Learner
Updated on ・9 min read

One of my goals this year is to publish my App KidzTokenz on Apple App Store. For that, I am planning to use Flutter and AWSAmplify.

In this post, we will integrate the Auth category into a Flutter App and run it on iOS.

Amplify Setup

I am going to use Amplify Admin UI to create the backend. Use the instruction I shared in the previous post (link below) to create a project of the name (AuthFlutter).

Configure and deploy the Authentication. We are going to use (Email) for verification.

Screen Shot 2021-01-13 at 1.24.25 PM

Project Setup

Using Terminal, create a new flutter project by running the command below


flutter create auth_for_flutter

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Next, let's open the project folder using the VS Code. Make sure the integrated terminal is in the ios folder.

Screen Shot 2021-01-12 at 1.43.06 PM

Run the following commands, and you will get a Podfile in the ios folder.


sudo gem install cocoapods

pod init

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Update the Podile as below


platform :ios, '13.0'

# CocoaPods analytics sends network stats synchronously affecting flutter build latency.
ENV['COCOAPODS_DISABLE_STATS'] = 'true'

project 'Runner', {
  'Debug' => :debug,
  'Profile' => :release,
  'Release' => :release,
}

def flutter_root
  generated_xcode_build_settings_path = File.expand_path(File.join('..', 'Flutter', 'Generated.xcconfig'), __FILE__)
  unless File.exist?(generated_xcode_build_settings_path)
    raise "#{generated_xcode_build_settings_path} must exist. If you're running pod install manually, make sure flutter pub get is executed first"
  end

  File.foreach(generated_xcode_build_settings_path) do |line|
    matches = line.match(/FLUTTER_ROOT\=(.*)/)
    return matches[1].strip if matches
  end
  raise "FLUTTER_ROOT not found in #{generated_xcode_build_settings_path}. Try deleting Generated.xcconfig, then run flutter pub get"
end

require File.expand_path(File.join('packages', 'flutter_tools', 'bin', 'podhelper'), flutter_root)

flutter_ios_podfile_setup

target 'Runner' do
  use_frameworks!
  use_modular_headers!

  flutter_install_all_ios_pods File.dirname(File.realpath(__FILE__))
end

post_install do |installer|
  installer.pods_project.targets.each do |target|
    flutter_additional_ios_build_settings(target)
  end
end


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In XCode, select your project in the Project Navigator and select the “Info” tab. Set the Deployment Target to at least 13.0.

Screen Shot 2021-01-12 at 2.13.21 PM

Open the App‘s pubspec.yaml and add the following dependencies below the line “sdk:flutter”.


dependencies:
  flutter:
    sdk: flutter
  amplify_core: '<1.0.0'
  amplify_auth_cognito: '<1.0.0'

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Run the command below in the in ios folder


pod install

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This is going to install the required Pods.

Screen Shot 2021-01-12 at 2.23.22 PM

Pull down the Amplify backend we created above by running the pull command from the Admin UI in the root folder of the App

Screen Shot 2021-01-13 at 4.20.06 PM

Answer the prompted questions, and once complete, you will get a confirmation as below.


Added backend environment config object to your project.
Run 'amplify pull' to sync upstream changes.

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Update the app‘s pubspec.yaml to add the image file we are going to use


# To add assets to your application, add an assets section, like this:
  assets:
     - assets/images/applogo.png

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Run the App to make sure it builds successfully

Screen Shot 2021-01-12 at 2.25.57 PM

The Implementation

We are going to use an enum for the authentication's status. Create the file below in the (lib) folder

account_screens_enum.dart


enum AccountStatus {
  sign_in,
  sign_up,
  reset_password,
  confirm_code,
  main_screen
}

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Next, let's create the widgets in (lib\widgets) folder.

sign_up.dart

To create an account.


import 'package:amplify_auth_cognito/amplify_auth_cognito.dart';
import 'package:amplify_core/amplify_core.dart';
import 'package:auth_for_flutter/account_screens_enum.dart';
import 'package:auth_for_flutter/widgets/confirm_signup.dart';
import 'package:auth_for_flutter/widgets/error_view.dart';
import 'package:flutter/material.dart';

class SignUpView extends StatefulWidget {
  final Function _displayAccountWidget;

  const SignUpView(this._displayAccountWidget);

  @override
  _SignUpViewState createState() => _SignUpViewState();
}

class _SignUpViewState extends State<SignUpView> {
  final emailController = TextEditingController();
  final passwordController = TextEditingController();
  bool _isSignedUp = false;
  DateTime signupDate;

  String _signUpError = "";
  List<String> _signUpExceptions = [];

  @override
  void initState() {
    super.initState();
  }

  void _setError(AuthError error) {
    setState(() {
      _signUpError = error.cause;
      _signUpExceptions.clear();
      error.exceptionList.forEach((el) {
        _signUpExceptions.add(el.exception);
      });
    });
  }

  void _signUp(BuildContext context) async {
    try {
      Map<String, dynamic> userAttributes = {
        "email": emailController.text.trim(),
        "preferred_username": emailController.text.trim(),
        // additional attributes as needed
      };
      SignUpResult res = await Amplify.Auth.signUp(
          username: emailController.text.trim(),
          password: passwordController.text.trim(),
          options: CognitoSignUpOptions(userAttributes: userAttributes));

      print(res.isSignUpComplete);
      setState(() {
        _isSignedUp = true;
      });
    } on AuthError catch (error) {
      _setError(error);
    }
  }

  @override
  Widget build(BuildContext context) {
    return Card(
      elevation: 2,
      child: Row(
        mainAxisAlignment: MainAxisAlignment.spaceEvenly,
        children: <Widget>[
          Expanded(
            child: Padding(
              padding: EdgeInsets.all(10.0),
              child: Column(
                children: [
                  Visibility(
                    visible: !_isSignedUp,
                    child: Column(children: [
                      TextFormField(
                        enableSuggestions: false,
                        decoration: const InputDecoration(
                          icon: Icon(Icons.email),
                          hintText: 'Email',
                          labelText: 'Email *',
                        ),
                        controller: emailController,
                        keyboardType: TextInputType.emailAddress,
                      ),
                      TextFormField(
                        obscureText: true,
                        enableSuggestions: false,
                        autocorrect: false,
                        decoration: const InputDecoration(
                          icon: Icon(Icons.lock),
                          hintText: 'Password',
                          labelText: 'Password *',
                        ),
                        controller: passwordController,
                      ),
                      const Padding(padding: EdgeInsets.all(10.0)),
                      FlatButton(
                        textColor:
                            Colors.black, // Theme.of(context).primaryColor,
                        color: Colors.amber,
                        onPressed: () => _signUp(context),
                        child: Text(
                          'Create Account',
                          style: TextStyle(fontWeight: FontWeight.bold),
                        ),
                      ),
                      FlatButton(
                        height: 5,
                        onPressed: _displaySignIn,
                        child: Text(
                          'Already registered? Sign In',
                          style: Theme.of(context).textTheme.subtitle2,
                        ),
                      ),
                    ]),
                  ),
                  Visibility(
                      visible: _isSignedUp,
                      child: Column(children: [
                        ConfirmSignup(emailController.text.trim(), _setError),
                      ])),
                  ErrorView(_signUpError, _signUpExceptions)
                ],
              ),
            ),
          ),
        ],
      ),
    );
  }

  void _displaySignIn() {
    widget._displayAccountWidget(AccountStatus.sign_in.index);
  }
}



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confirm_signup.dart

To submit the signup confirmation code.


import 'package:amplify_auth_cognito/amplify_auth_cognito.dart';
import 'package:amplify_core/amplify_core.dart';
import 'package:auth_for_flutter/screens/next_screen.dart';
import 'package:flutter/material.dart';

class ConfirmSignup extends StatelessWidget {
  final codeController = TextEditingController();
  final String userName;
  final Function setError;

  ConfirmSignup(this.userName, this.setError);

  void _skip_confirm_signup(BuildContext context) {
    _go_to_NextScreen(context);
  }

  void _confirm_signup(BuildContext context) async {
    try {
      SignUpResult res = await Amplify.Auth.confirmSignUp(
          username: this.userName,
          confirmationCode: codeController.text.trim());

      _go_to_NextScreen(context);
    } on AuthError catch (e) {
      setError(e);
    }
  }

  void _go_to_NextScreen(BuildContext context) {
    Navigator.of(context).pushReplacement(
      MaterialPageRoute(
        builder: (_) {
          return NextScreen();
        },
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Container(
      // decoration: BoxDecoration(borderRadius: BorderRadius.circular(20)),
      padding: EdgeInsets.all(5),
      child: Column(
        children: [
          TextFormField(
              controller: codeController,
              decoration: const InputDecoration(
                icon: Icon(Icons.confirmation_number),
                hintText: 'The code we sent you',
                labelText: 'Confirmation Code *',
              )),
          FlatButton(
            textColor: Colors.black, // Theme.of(context).primaryColor,
            color: Colors.amber,
            onPressed: () => _confirm_signup(context),
            child: Text(
              'Confirm Sign Up',
              style: TextStyle(fontWeight: FontWeight.bold),
            ),
          ),
        ],
      ),
    );
  }
}


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reset_password.dart

To request a password reset operation.


import 'package:amplify_auth_cognito/amplify_auth_cognito.dart';
import 'package:amplify_core/amplify_core.dart';
import 'package:auth_for_flutter/account_screens_enum.dart';
import 'package:auth_for_flutter/widgets/confirm_reset_password.dart';
import 'package:auth_for_flutter/widgets/error_view.dart';
import 'package:flutter/material.dart';

class ResetPasswordView extends StatefulWidget {
  final Function _displayAccountWidget;

  const ResetPasswordView(this._displayAccountWidget);

  @override
  _ResetPasswordViewState createState() => _ResetPasswordViewState();
}

class _ResetPasswordViewState extends State<ResetPasswordView> {
  final emailController = TextEditingController();
  bool _isPasswordReset = false;

  String _signUpError = "";
  List<String> _signUpExceptions = [];

  @override
  void initState() {
    super.initState();
  }

  void _setError(AuthError error) {
    setState(() {
      _signUpError = error.cause;
      _signUpExceptions.clear();
      error.exceptionList.forEach((el) {
        _signUpExceptions.add(el.exception);
      });
    });
  }

  void _resetPassword(BuildContext context) async {
    try {
      ResetPasswordResult res = await Amplify.Auth.resetPassword(
        username: emailController.text.trim(),
      );

      setState(() {
        _isPasswordReset = true;
      });
    } on AuthError catch (e) {
      setState(() {
        _signUpError = e.cause;
        _signUpExceptions.clear();
        e.exceptionList.forEach((el) {
          _signUpExceptions.add(el.exception);
        });
      });
    }
  }

  @override
  Widget build(BuildContext context) {
    return Card(
      elevation: 2,
      child: Row(
        mainAxisAlignment: MainAxisAlignment.spaceEvenly,
        children: <Widget>[
          Expanded(
            child: Padding(
              padding: EdgeInsets.all(10.0),
              child: Column(
                children: [
                  Visibility(
                    visible: !_isPasswordReset,
                    child: Column(children: [
                      TextFormField(
                        enableSuggestions: false,
                        decoration: const InputDecoration(
                          icon: Icon(Icons.email),
                          hintText: 'Email',
                          labelText: 'Email *',
                        ),
                        controller: emailController,
                        keyboardType: TextInputType.emailAddress,
                      ),
                      const Padding(padding: EdgeInsets.all(10.0)),
                      FlatButton(
                        textColor:
                            Colors.black, // Theme.of(context).primaryColor,
                        color: Colors.amber,
                        onPressed: () => _resetPassword(context),
                        child: Text(
                          'Reset Password',
                          style: TextStyle(fontWeight: FontWeight.bold),
                        ),
                      ),
                      FlatButton(
                        height: 5,
                        onPressed: _displayCreateAccount,
                        child: Text(
                          'Create Account',
                          style: Theme.of(context).textTheme.subtitle2,
                        ),
                      ),
                    ]),
                  ),
                  Visibility(
                      visible: _isPasswordReset,
                      child: Column(children: [
                        ConfirmResetPassword(
                            emailController.text.trim(), _setError),
                      ])),
                  ErrorView(_signUpError, _signUpExceptions)
                ],
              ),
            ),
          ),
        ],
      ),
    );
  }

  void _displayCreateAccount() {
    widget._displayAccountWidget(AccountStatus.sign_up.index);
  }
}


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confirm_reset_password.dart

To submit the confirmation code and the new password.


import 'package:amplify_auth_cognito/amplify_auth_cognito.dart';
import 'package:amplify_core/amplify_core.dart';
import 'package:auth_for_flutter/screens/next_screen.dart';
import 'package:flutter/material.dart';

class ConfirmResetPassword extends StatelessWidget {
  final codeController = TextEditingController();
  final emailController = TextEditingController();
  final passwordController = TextEditingController();
  final String userName;
  final Function setError;

  ConfirmResetPassword(this.userName, this.setError);

  void _confirm_password_reset(BuildContext context) async {
    try {
      await Amplify.Auth.confirmPassword(
          username: this.userName,
          newPassword: passwordController.text.trim(),
          confirmationCode: codeController.text.trim());
      _go_to_NextScreen(context);
    } on AuthError catch (e) {
      setError(e);
    }
  }

  void _go_to_NextScreen(BuildContext context) {
    Navigator.of(context).pushReplacement(
      MaterialPageRoute(
        builder: (_) {
          return NextScreen();
        },
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Container(
      // decoration: BoxDecoration(borderRadius: BorderRadius.circular(20)),
      padding: EdgeInsets.all(5),
      child: Column(
        children: [
          TextFormField(
            enableSuggestions: false,
            decoration: const InputDecoration(
              icon: Icon(Icons.email),
              hintText: 'Email',
              labelText: 'Email *',
            ),
            controller: emailController,
            keyboardType: TextInputType.emailAddress,
          ),
          TextFormField(
            obscureText: true,
            enableSuggestions: false,
            autocorrect: false,
            decoration: const InputDecoration(
              icon: Icon(Icons.lock),
              hintText: 'New Password',
              labelText: 'New Password *',
            ),
            controller: passwordController,
          ),
          TextFormField(
              controller: codeController,
              decoration: const InputDecoration(
                icon: Icon(Icons.confirmation_number),
                hintText: 'The code we sent you',
                labelText: 'Confirmation Code *',
              )),
          FlatButton(
            textColor: Colors.black, // Theme.of(context).primaryColor,
            color: Colors.amber,
            onPressed: () => _confirm_password_reset(context),
            child: Text(
              'Reset Password & Sign In',
              style: TextStyle(fontWeight: FontWeight.bold),
            ),
          ),
        ],
      ),
    );
  }
}


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sign_in.dart

The sign-in operation


import 'package:amplify_auth_cognito/amplify_auth_cognito.dart';
import 'package:amplify_core/amplify_core.dart';
import 'package:auth_for_flutter/account_screens_enum.dart';
import 'package:auth_for_flutter/screens/next_screen.dart';
import 'package:auth_for_flutter/widgets/error_view.dart';
import 'package:flutter/material.dart';

class SignInView extends StatefulWidget {
  final Function _displayAccountWidget;

  const SignInView(this._displayAccountWidget);

  @override
  _SignInViewState createState() => _SignInViewState();
}

class _SignInViewState extends State<SignInView> {
  final emailController = TextEditingController();
  final passwordController = TextEditingController();
  String _signUpError = "";
  List<String> _signUpExceptions = [];

  @override
  void initState() {
    super.initState();
  }

  void _setError(AuthError error) {
    setState(() {
      _signUpError = error.cause;
      _signUpExceptions.clear();
      error.exceptionList.forEach((el) {
        _signUpExceptions.add(el.exception);
      });
    });
  }

  void _signIn() async {
    // Sign out before in case a user is already signed in
    // If a user is already signed in - Amplify.Auth.signIn will throw an exception
    try {
      await Amplify.Auth.signOut();
    } on AuthError catch (e) {
      print(e);
    }

    try {
      SignInResult res = await Amplify.Auth.signIn(
          username: emailController.text.trim(),
          password: passwordController.text.trim());
      _go_to_NextScreen(context);
    } on AuthError catch (e) {
      setState(() {
        _signUpError = e.cause;
        _signUpExceptions.clear();
        e.exceptionList.forEach((el) {
          _signUpExceptions.add(el.exception);
        });
      });
    }
  }

  void _go_to_NextScreen(BuildContext context) {
    Navigator.of(context).pushReplacement(
      MaterialPageRoute(
        builder: (_) {
          return NextScreen();
        },
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Card(
      elevation: 2,
      child: Row(
        mainAxisAlignment: MainAxisAlignment.spaceEvenly,
        children: <Widget>[
          Expanded(
            // wrap your Column in Expanded
            child: Padding(
              padding: EdgeInsets.all(10.0),
              child: Column(
                children: [
                  TextFormField(
                    controller: emailController,
                    decoration: const InputDecoration(
                      icon: Icon(Icons.email),
                      hintText: 'Enter your email',
                      labelText: 'Email *',
                    ),
                  ),
                  TextFormField(
                    obscureText: true,
                    controller: passwordController,
                    decoration: const InputDecoration(
                      icon: Icon(Icons.lock),
                      hintText: 'Enter your password',
                      labelText: 'Password *',
                    ),
                  ),
                  const Padding(padding: EdgeInsets.all(10.0)),
                  FlatButton(
                    textColor: Colors.black, // Theme.of(context).primaryColor,
                    color: Colors.amber,
                    onPressed: _signIn,
                    child: const Text(
                      'Sign In',
                      style: TextStyle(fontWeight: FontWeight.bold),
                    ),
                  ),
                  Row(
                    mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                    children: <Widget>[
                      FlatButton(
                        height: 5,
                        onPressed: _displayCreateAccount,
                        child: Text(
                          'Create Account',
                          style: Theme.of(context).textTheme.subtitle2,
                        ),
                      ),
                      FlatButton(
                        height: 5,
                        onPressed: _displayResetPassword,
                        child: Text(
                          'Reset Password',
                          style: Theme.of(context).textTheme.subtitle2,
                        ),
                      ),
                    ],
                  ),
                  ErrorView(_signUpError, _signUpExceptions)
                ],
              ),
            ),
          ),
        ],
      ),
    );
  }

  void _displayCreateAccount() {
    widget._displayAccountWidget(AccountStatus.sign_up.index);
  }

  void _displayResetPassword() {
    widget._displayAccountWidget(AccountStatus.reset_password.index);
  }
}


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error_view.dart

Display the error messages.


import 'package:flutter/material.dart';

class ErrorView extends StatelessWidget {
  final String error;
  final List<String> exceptions;

  ErrorView(this.error, this.exceptions);

  @override
  Widget build(BuildContext context) {
    // We do not recognize your username and/or password. Please try again.
    if (error.isNotEmpty || exceptions.length > 0) {
      return Column(children: <Widget>[
        Text('Error: $error',
            textAlign: TextAlign.center,
            overflow: TextOverflow.visible,
            style: TextStyle(
              fontWeight: FontWeight.bold,
              color: Theme.of(context).errorColor,
            )),
        if (exceptions.length > 0) ...[_showExceptions(context)]
      ]);
    } else {
      return Container();
    }
  }

  _showExceptions(context) {
    return Column(
        children: exceptions
            .map((item) => new Text(item + " ",
                style: TextStyle(
                  fontWeight: FontWeight.bold,
                  color: Theme.of(context).errorColor,
                )))
            .toList());
  }
}


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We will have three screens in the App. Create the screens below in the (lib\screens) folder

loading_screen.dart


import 'package:flutter/material.dart';

class LoadingScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('BatMan App')),
      body: Container(
        color: Color(0xff90CCE6),
        child: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              Container(
                color: Color(0xffE1E5E4),
                height: 200,
                child: Image.asset(
                  'assets/images/applogo.png',
                  fit: BoxFit.cover,
                ),
              ),
              Padding(
                padding: const EdgeInsets.all(8.0),
                child: Center(
                  child: CircularProgressIndicator(),
                ),
              ),
            ],
          ),
        ),
      ),
    );
  }
}


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main_screen.dart


import 'package:amplify_auth_cognito/amplify_auth_cognito.dart';
import 'package:amplify_core/amplify_core.dart';
import 'package:auth_for_flutter/account_screens_enum.dart';
import 'package:auth_for_flutter/screens/next_screen.dart';
import 'package:auth_for_flutter/widgets/reset_password.dart';
import 'package:auth_for_flutter/widgets/sign_in.dart';
import 'package:auth_for_flutter/widgets/sign_up.dart';
import 'package:flutter/material.dart';

class MainScreen extends StatefulWidget {
  @override
  _MainScreenState createState() => _MainScreenState();
}

class _MainScreenState extends State<MainScreen> {
  var _accountWidget;

  @override
  initState() {
    super.initState();
    _fetchSession();
  }

  void _fetchSession() async {
    // Sign out before in case a user is already signed in
    try {
      await Amplify.Auth.signOut();
    } on AuthError catch (e) {
      print(e);
    }
    _accountWidget = AccountStatus.sign_in.index;
    _displayAccountWidget(_accountWidget);
  }

  void _go_to_NextScreen(BuildContext context) {
    Navigator.of(context).pushReplacement(
      MaterialPageRoute(
        builder: (_) {
          return NextScreen();
        },
      ),
    );
  }

  void _displayAccountWidget(int accountStatus) {
    setState(() {
      _accountWidget = AccountStatus.values[accountStatus];
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('BatMan App'),
      ),
      body: Container(
        color: Color(0xffE1E5E4),
        child: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              Container(
                color: Color(0xffE1E5E4),
                height: 200,
                child: Image.asset(
                  'assets/images/applogo.png',
                  fit: BoxFit.cover,
                ),
              ),
              Padding(
                padding: const EdgeInsets.all(8.0),
                child: Column(children: [
                  Visibility(
                    visible: _accountWidget == AccountStatus.sign_in,
                    child: SignInView(_displayAccountWidget),
                  ),
                  Visibility(
                    visible: _accountWidget == AccountStatus.sign_up,
                    child: SignUpView(_displayAccountWidget),
                  ),
                  Visibility(
                    visible: _accountWidget == AccountStatus.reset_password,
                    child: ResetPasswordView(_displayAccountWidget),
                  ),
                  Visibility(
                    visible: _accountWidget == AccountStatus.main_screen,
                    child: NextScreen(),
                  ),
                ]),
              ),
            ],
          ),
        ),
      ),
    );
  }
}


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next_screen.dart


import 'package:auth_for_flutter/screens/main_screen.dart';
import 'package:flutter/material.dart';

class NextScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('BatMan App')),
      body: Container(
        color: Color(0xffE1E5E4),
        child: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              Container(
                color: Color(0xffE1E5E4),
                height: 200,
                child: Image.asset(
                  'assets/images/applogo.png',
                  fit: BoxFit.cover,
                ),
              ),
              Padding(
                padding: const EdgeInsets.all(20.0),
                child: Center(
                  child: Text(
                    'I\'m BATMAN',
                    style: TextStyle(fontWeight: FontWeight.bold, fontSize: 30),
                  ),
                ),
              ),
              Padding(
                padding: const EdgeInsets.all(20.0),
                child: Center(
                  child: RaisedButton(
                    color: Colors.lightBlue,
                    onPressed: () => _signOut(context),
                    child: Text(
                      'Sign Out',
                      style: TextStyle(
                        fontWeight: FontWeight.bold,
                        fontSize: 20,
                      ),
                    ),
                  ),
                ),
              ),
            ],
          ),
        ),
      ),
    );
  }

  void _signOut(BuildContext context) {
    Navigator.of(context).pushReplacement(
      MaterialPageRoute(
        builder: (_) {
          return MainScreen();
        },
      ),
    );
  }
}



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Cover image Obi Onyeador on Unsplash

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