Problem implementing shared_preferrences in flutter - flutter

Question

The following code is part of my login screen. I am using shared_preferences to save the remember me checkbox and the user name. The checkbox value is working, but the user name is not being set. I know it is being saved because I can see the value using print. But I guess it is being set too late, as my TextField is blank. Any ideas?
class RmoLogin extends StatefulWidget {
static const String id = 'login_screen';
#override
_RmoLoginState createState() => _RmoLoginState();
}
class _RmoLoginState extends State<RmoLogin> {
final TextStyle style = TextStyle(fontFamily: 'Montserrat', fontSize: 20.0);
final TextEditingController usernameController = TextEditingController();
final TextEditingController passwordController = TextEditingController();
final GlobalKey<ScaffoldState> _scaffoldKey = new GlobalKey<ScaffoldState>();
bool showSpinner = false;
bool rememberMe = false;
String userName = '';
_saveRememberUser() async {
SharedPreferences prefs = await SharedPreferences.getInstance();
prefs.setString('username', usernameController.text);
prefs.setBool('remember', rememberMe);
}
_getRememberUser() async {
SharedPreferences prefs = await SharedPreferences.getInstance();
userName = prefs.getString('username') ?? '';
rememberMe = prefs.getBool('remember') ?? false;
}
#override
void initState() {
super.initState();
_getRememberUser();
if (rememberMe) {
usernameController.text = userName;
}
}
#override
Widget build(BuildContext context) {
final userField = UserTextField(style: style, usernameController: usernameController);
final passwordField = PasswordTextField(style: style, passwordController: passwordController);
final rememberMeCheckbox = Checkbox(
value: rememberMe,
onChanged: (newValue) {
setState(() {
rememberMe = newValue;
});
},
);

Answer 1

Because the SharedPreferences instantiation is asynchronous and the build method itself is not, by the time the instance is created and the value is accessed, the build method would have already been called and your widgets built.
However, For things like SharedPreferences and databases, the best way to implement them is to use the Singleton approach, i.e, one instance that you can use across the entire application.
In this case instead of creating a new SharedPreferences instance whenever either method is called, it will be best to create a single instance of it and use that instance to update the set and get the values.
You could also create a service for the SharedPreferences which you could use across the entire application.
class SharedPreferencesService {
final SharedPreferences _prefs;
SharedPreferencesService(this._prefs);
// define methods here
}
Then in your main method, you can create an instance of SharedPreferences and use it to initialize the SharedPreferencesService.
eg.
SharedPreferencesService service;
Future<void> main() async {
// flutter will complain if this isn't present
WidgetsFlutterBinding.ensureInitialized();
final prefs = await SharedPreferences.getInstance();
service = SharedPreferencesService(prefs);
runApp(YourApp());
}
Then wherever you want to use it in your app, you can call the method name on the service. It is best to use Dependency Injection for the SharedPreferencesService though, you can try the get_it library.

Answer 2

Just a brief look.... but
You are calling _getRememberUser synchronously within initState() when it is an async method
initState() isn't the correct place to be calling it as initState() itself is a synchronus #override.
My solution would be to use a FutureBuilder in your build() method, and call _getRememberUser there.

Answer 3

You just need to update the state that's it check the below solution:
bool rememberMe = false;
String userName = '';
#override
void initState() {
// TODO: implement initState
super.initState();
_getRememberUser();
}
_getRememberUser() async {
SharedPreferences prefs = await SharedPreferences.getInstance();
setState(() {
userName = prefs.getString('username') ?? '';
rememberMe = prefs.getBool('remember')?? false;
});
if (rememberMe) {
usernameController.text = userName;
}
print(userName +'-->'+rememberMe.toString());
}
Happy Coding!!