How to use shared preferences to keep user logged in flutter?

Question

I want to keep the user logged in after the user successfully logsin in flutter. I am using a REST API to retrieve the user name and password of the user. But I want to save those details so that the user can stay logged in. My current situation is i can successfully log the user in but when i restart the app i have to login again so i need to save the details of the user in a shared preference so that the user can stay logged for the entire session until logout.But i am unable to do that so please help me with it. Thanks in advance

This is the code i have for my login page. I have removed the UI contents which should be inside the listview as those are not that relevant.

Login.dart

import 'dart:convert';

import 'package:flutter/material.dart';
import 'package:restaurant_app/globalVar.dart';
import 'package:restaurant_app/homescreen.dart';
import 'package:restaurant_app/models/auth.dart';
import 'package:restaurant_app/signup.dart';
import 'package:http/http.dart' as http;
import 'package:restaurant_app/utils/authutils.dart';
import 'package:shared_preferences/shared_preferences.dart';

class SignIn extends StatefulWidget {

    SignIn({ Key key, this.post }): super(key: key);

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

class _SignInState extends State<SignIn> with SingleTickerProviderStateMixin 
    {
    TabController controller;
    TextEditingController _email = new TextEditingController();
    TextEditingController _password = new TextEditingController();
    bool loading;

    final GlobalKey < ScaffoldState > _scaffoldKey = new GlobalKey<ScaffoldState>
        ();

    @override
    void initState() {
        // TODO: implement initState
        super.initState();
        _fetchSessionAndNavigate();
        controller = new TabController(length: 2, vsync: this);
        loading = false;
    }

    @override
    void dispose() {
        // TODO: implement dispose
        super.dispose();
        controller.dispose();
        setState(() {
            loading = false;
        });
        _email.dispose();
        _password.dispose();
    }

    final GlobalKey < FormState > _formKey = GlobalKey<FormState>();
    bool _autoValidate = false;

    _login(username, password) async {
        setState(() {
            loading = true;
        });

        var body = json.encode({
            "username": username,
            "password": password,
        });

        Map < String, String > headers = {
            'Content-type': 'application/json',
                'Accept': 'application/json',
      };

        await http
            .post("${GlobalVar.Ip}/wp-json/jwt-auth/v1/token",
                body: body, headers: headers)
            .then((response) {
                var body = json.decode(response.body);
                //var response1;

                if (response.statusCode == 200) {
                    // TODO: you need to store body['token'] to use in some authentication
                    loading = false;
                    Navigator.pushReplacement(context,
                        MaterialPageRoute(builder: (BuildContext ctx) => HomePage()));
    } else {
        // TODO: alert message
        final snackBar = SnackBar(
            content: Text(body['message'].toString().trim()),
        );
        _scaffoldKey.currentState.showSnackBar(snackBar);
    }
    setState(() {
        loading = false;
    });
});
      }

@override
Widget build(BuildContext context) {
    return Scaffold(
        key: _scaffoldKey,
        resizeToAvoidBottomPadding: false,
        body: Container(
            decoration: BoxDecoration(
                image: DecorationImage(
                    image: AssetImage('images/art.png'),
                    fit: BoxFit.fill,
                    colorFilter: ColorFilter.mode(
                        Colors.white12.withOpacity(0.2), BlendMode.dstATop),
                ),
            ),
            child: ListView();
}

Answer 1

You can navigate to the Login page if the user details are saved in the storage else to the Home page with the below code

Future<void> main() async {
  SharedPreferences prefs = await SharedPreferences.getInstance();
  var email = prefs.getString('email');
  print(email);
  runApp(MaterialApp(home: email == null ? Login() : Home()));
}

Save the required user details after the successful login

class Login extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: RaisedButton(
          onPressed: () async {
            //after the login REST api call && response code ==200
            SharedPreferences prefs = await SharedPreferences.getInstance();
            prefs.setString('email', 'useremail@gmail.com');
            Navigator.pushReplacement(context,
                MaterialPageRoute(builder: (BuildContext ctx) => Home()));
          },
          child: Text('Login'),
        ),
      ),
    );
  }
}

clear the details on logout

class Home extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Home'),
      ),
      body: Center(
        child: RaisedButton(
          onPressed: () async {
            SharedPreferences prefs = await SharedPreferences.getInstance();
            prefs.remove('email');
            Navigator.pushReplacement(context,
                MaterialPageRoute(builder: (BuildContext ctx) => Login()));
          },
          child: Text('Logout'),
        ),
      ),
    );
  }
}

Hope it helps!