Saving changing variable value in flutter - flutter

Question

I want to save a variable's value that changes every 5 seconds then read it. I have already tried saving it to shared preferences then reading it but the problem with that was that the value was only saved one time and did not save the changes done to the variable. Is there a way to implement that in flutter?
class _MyAppState extends State<MyApp> {
void initState() {
super.initState();
Future.delayed(Duration.zero, () {
_connect();
});
}
...
void predict(List<double> v) async {
SharedPreferences prefs = await SharedPreferences.getInstance();
List<List<double>> L=List<List<double>>.filled(1, [0], growable: true);
L[0]=v;
...
String res=response.body;
Map R = json.decode(res);
var _list = R.values.toList();
print(res);
Proba= double.parse(_list[1]);
await prefs.setDouble('Proba', Proba);
}
....
class Page extends StatefulWidget {
Page({Key key, this.title}) : super(key: key);
final String title;
#override
PageState createState() => PageState();
}
class PageState extends State<Page> {
.....
Future<double> _getProbaFromSharedPref() async {
SharedPreferences prefs = await SharedPreferences.getInstance();
return prefs.getDouble("Proba") ?? 0;
}
#override
void initState() {
super.initState();
Location1=_getCurrentLocation();
_getStringFromSharedPref();
_getProbaFromSharedPref().then((s) {
Value = s;
});
Future.delayed(Duration.zero, () {
_check();
});
}
}
In the code I tried saving the variable in sharedPreferences then reading it, but I have no clue on how to reload it everytime it changes.