Flutter : method call on null when using shared preference - api

Question

I want to use shared preference to keep user login and i'm using api with provider .
i tried to put it in main but i don't how to do it because i have two different page to go so i was used it in the first page but i found another error
[ERROR:flutter/lib/ui/ui_dart_state.cc(177)] Unhandled Exception:
NoSuchMethodError: The method 'login' was called on null. E/flutter (
4199): Receiver: null
and this is the method which i used
UserProvider userProvider;
ServiceProvider serviceProvider;
bool alive = true;
bool isLoading = false;
var page;
#override
initState() {
init();
super.initState();
}
init() async {
SharedPreferences prefs = await SharedPreferences.getInstance();
bool language = prefs.getBool('language');
bool type = prefs.getBool('type');
bool login = prefs.getBool('islog');
if (alive) {
if (language == true && type == true && login == true) {
signIn();
} else if ((language == true && type == false && login == true)) {
visitor();
}
} else {
if (alive) {
setState(() {
isLoading = false;
});
}
}
}
signIn() async {
//var res = await userProvider.residentLogin(context, phone, pass);
SharedPreferences prefs = await SharedPreferences.getInstance();
var phone = prefs.getString('phone');
String pass = prefs.getString("pass");
bool type = prefs.getBool('type');
print("Shared ***************resident********************************");
await userProvider.residentLogin(context, phone, pass);
await serviceProvider.getHomeServiceList(context);
await serviceProvider.getAdsList(context);
await serviceProvider.getVideosList(context);
Navigator.pushReplacement(context,
MaterialPageRoute(builder: (context) => ResidentBottomTab()));
print('Hello Tourist !!');
}
visitor() async {
SharedPreferences prefs = await SharedPreferences.getInstance();
var phone = prefs.getString('phone');
String pass = prefs.getString("pass");
await userProvider.login(context, phone, pass);
await serviceProvider.getVisitorAdsList(context);
await serviceProvider.getVisitorVideosList(context);
bool type = prefs.getBool('type');
print("Shared ******************visitor*****************************");
if (alive) {
Navigator.pushReplacement(
context, MaterialPageRoute(builder: (context) => VisitorHome()));
print('Hello Tourist !!');
}
}
#override
void dispose() {
alive = false;
super.dispose();
}
login method
Future<VisitorLoginModel> login(BuildContext context, phone, pass) async {
final Map<String, dynamic> body = {
'phone': phone,
'password': pass,
'token': '123',
'serial_number': '123',
'lang': 'en',
'os': 'android',
};
_isLoading = true;
notifyListeners();
print('Starting request');
http.Response response = await http.post(Environment.userLogin,
body: json.encode(body), headers: Environment.requestHeader);
print('Completed request');
print('user SignUp response : ${response.body}');
//print(body.toString());
Map<String, dynamic> res = json.decode(response.body);
var results;
if (res['status'] == 1) {
// login successful
_visitorLoginModel = parseVisitorLogin(response.body);
Provider.of<LoginVisitorUserProvider>(context, listen: false).userData =
visitorLoginModel;
Provider.of<LoginVisitorUserProvider>(context, listen: false)
.sessionToken = visitorLoginModel.data.token;
headers = Provider.of<LoginVisitorUserProvider>(context, listen: false)
.httpHeader;
// print('token');
print('this is session token' +
Provider.of<LoginVisitorUserProvider>(context, listen: false)
.sessionToken);
} else {
// login failed;
results =
FailedRequest(code: 401, message: res['massage'], status: false);
}
_isLoading = false;
notifyListeners();
return visitorLoginModel;
}
so anyone has an idea to solve this case !

Answer 1

The method call await userProvider.login(context, phone, pass); is being done on a non initialized variable. UserProvider userProvider; has been declared but not initialized

Answer 2

The issue here is the userProvider is being declared but not initialized and the same goes for serviceProvider
In Flutter any uninitialized variable will implicitly assigned with null
So, at the line await userProvider.login(context, phone, pass); where you call login method in which userProvider is not only initialized
To Solve the issue do the following,
In initState,
userProvider = Provider.of<UserProvider>(context, listen: false);