Keeping user logged in, in the app with setState() - flutter

Question

I am trying to keep the user of my app logged in until they logout. This is an app that accesses an api for authentication. I want to keep the user logged in using the setState method and not the token authentication method. I am able to successfully login but when I close and open the app again, I have to re-login.
Below are the files with the related code using the setState function. I am unable to find my error.
main.dart:
void main() => runApp(new MyApp());
class MyApp extends StatefulWidget {
#override
_MyAppState createState() => new _MyAppState();
}
class _MyAppState extends State<MyApp> {
#override
Widget build(BuildContext context) {
return new MaterialApp(
title: "Splash and Token Authentication",
routes: <String, WidgetBuilder>{
"/HomeScreen": (BuildContext context) => HomeScreen(),
"/LoginScreen": (BuildContext context) => LoginScreen(),
},
//state variable is in loginScreen.dart file
home: ((state == loginState.LOGGED_IN)? HomeScreen():LoginScreen())
);
}
#override
void initState() {
super.initState();
}
}
loginScreen.dart:
import ...
enum loginState{ LOGGED_IN, LOGGED_OUT}
loginState state;
const URL = "http://www.google.com";
class LoginScreen extends StatefulWidget {
#override
State<StatefulWidget> createState() {
return new LoginScreenState();
}
}
class LoginScreenState extends State<LoginScreen> {
final TextEditingController _userNameController = TextEditingController();
final TextEditingController _passwordController = TextEditingController();
String _welcomeString = "";
Future launchURL(String url) async {
if(await canLaunch(url)) {
await launch(url, forceSafariVC: true, forceWebView: true);
} else {
showDialogSingleButton(context, "Unable to reach your website.", "Currently unable to reach the website $URL. Please try again at a later time.", "OK");
}
}
#override
void initState() {
super.initState();
_saveCurrentRoute("/LoginScreen");
}
_saveCurrentRoute(String lastRoute) async {
SharedPreferences preferences = await SharedPreferences.getInstance();
await preferences.setString('LastScreenRoute', lastRoute);
}
}
#override
Widget build(BuildContext context) {
//LoginScreen UI
}
}
homeScreen.dart:
import ...
class HomeScreen extends StatefulWidget {
#override
_HomeScreenState createState() => _HomeScreenState();
}
class _HomeScreenState extends State<HomeScreen> {
#override
void initState() {
super.initState();
_saveLoginState();
_saveCurrentRoute("/HomeScreen");
}
_saveCurrentRoute(String lastRoute) async {
SharedPreferences preferences = await SharedPreferences.getInstance();
await preferences.setString('LastScreenRoute', lastRoute);
}
Future<void> _saveLoginState() async{
setState(() {
state = loginState.LOGGED_IN;
});
}
#override
Widget build(BuildContext context) {
//HomeScreen UI
}

Answer 1

use onGenerateRoute inside your MaterialApp
Here you can set initialRoute, after log in change SharedPreferences to your loginScreen route. and then you can get route when app is started.
#override
Widget build(BuildContext context) {
String initialRoute = '/';
return MaterialApp(
theme: _themeData,
onGenerateRoute: (s) => _getCurrentRoute(s),
initialRoute: initialRoute,
);
}
_getCurrentRoute(RouteSettings settings) {
print(settings.arguments);
switch (settings.name) {
case '/':
return MaterialPageRoute(
builder: (context) => PageRouter(
child: LogInPage(),
isSearchBar: false,
));
case '/home':
return MaterialPageRoute(
builder: (context) => PageRouter(
child: Home(),
isSearchBar: true,
));
case '/plp_page':
return MaterialPageRoute(
builder: (context) => PageRouter(
child: PlpPage(),
isSearchBar: false,
));
case '/pdp_page':
return MaterialPageRoute(builder: (context) => PdpPage());
case '/cart_page':
return MaterialPageRoute(
builder: (context) => PageRouter(
child: CartPage(),
isSearchBar: false,
));
}
}

Answer 2

You are looking for the shared_preferences package.
You need to Save your Data into Shared Preference when user logs in, and when user log out you need to clear all the Shared Preference.
While When user opens up app again you need to check if the Shared Preference has data of user or not.
Sample Code:
//Initialise SharedPreferences
SharedPreferences prefs = await SharedPreferences.getInstance();
//set some value in it.
//In your case your user data like some id, email or anything
await prefs.setInt('key', value);
//Getting data from preference.
final someName = prefs.getInt('key')