How to store selected value in a string so that after restart app it shows last selected value?

I'm setting up flutter local notification, all is going well but i want to store the selected value in a text so if the app restart it will show selected value rather then resetting to default. For example if I choose notification at 08:08:08 so after selecting it and restarting app whenever i go to notification selection time it should show 08:08:08(last selected value).

i have tried setstate(){}; but value always reset after restarting app. here is my code.

import 'dart:async';
import 'package:flutter/material.dart';
import 'package:flutter_local_notifications/flutter_local_notifications.dart';
import 'package:flutter_datetime_picker/flutter_datetime_picker.dart';
import 'package:fluttertoast/fluttertoast.dart';
class SettingPage extends StatefulWidget {
  @override
  _SettingPage createState() => _SettingPage();
}

  class _SettingPage extends State<SettingPage> {
  ///Flutter Local Notification
  FlutterLocalNotificationsPlugin flutterLocalNotificationsPlugin;
  String notifyTime ="your time";
  String nhour ="";
  String nminutes ="";
  String nseconds ="";


    @override
    initState() {
    super.initState();
    // initialise the plugin. app_icon needs to be a added as a drawable 
    resource to the Android head project
    // If you have skipped STEP 3 then change app_icon to @mipmap/ic_launcher
    var initializationSettingsAndroid =
    new AndroidInitializationSettings('@mipmap/ic_launcher');
    var initializationSettingsIOS = new IOSInitializationSettings();
    var initializationSettings = new InitializationSettings(
        initializationSettingsAndroid, initializationSettingsIOS);

    flutterLocalNotificationsPlugin = new FlutterLocalNotificationsPlugin();
    flutterLocalNotificationsPlugin.initialize(initializationSettings);
    }
    Future _showNotificationWithDefaultSound() async {
    var androidPlatformChannelSpecifics = new AndroidNotificationDetails(
        'your channel id', 'your channel name', 'your channel description',
        importance: Importance.Max, priority: Priority.High);
    var iOSPlatformChannelSpecifics = new IOSNotificationDetails();
    var platformChannelSpecifics = new NotificationDetails(
        androidPlatformChannelSpecifics, iOSPlatformChannelSpecifics);
    await flutterLocalNotificationsPlugin.show(
      0,
      'Learn Local Notification',
      'A Local Notification On Button Click',
      platformChannelSpecifics,
      payload: 'Default_Sound',
    );
  }

  Future scheuleAtParticularTime(DateTime timee) async {
    var time = Time(timee.hour, timee.minute, timee.second);

    print(time.toString());
    var androidPlatformChannelSpecifics = new AndroidNotificationDetails(
        'repeatDailyAtTime channel id',
        'repeatDailyAtTime channel name',
        'repeatDailyAtTime description');
    var iOSPlatformChannelSpecifics = new IOSNotificationDetails();
    var platformChannelSpecifics = new NotificationDetails(
        androidPlatformChannelSpecifics, iOSPlatformChannelSpecifics);
    flutterLocalNotificationsPlugin.showDailyAtTime(0, 'Hey! Check your 
    today`s horoscope ',
        'Login now to see your today`s horoscope !', time, 
    platformChannelSpecifics);
    print('scheduled');
    Fluttertoast.showToast(
        msg:
        "Notification Scheduled for ${time.hour} : ${time.minute} : 
    ${time.second}",
        toastLength: Toast.LENGTH_SHORT,
        gravity: ToastGravity.BOTTOM,
        // also possible "TOP" and "CENTER"
        backgroundColor: Colors.grey,
        textColor: Colors.white);
    setState(() {
      nhour = time.hour.toString();
      nminutes=time.minute.toString();
      nseconds=time.second.toString();
      notifyTime=nhour+" : "+nminutes+" : "+nseconds;

    });
  }
  //function ends
 @override
  Widget build(BuildContext context) {
    return Scaffold(backgroundColor: Theme.of(context).primaryColor,
      appBar: AppBar(backgroundColor: Theme.of(context).primaryColor,
        leading: IconButton(icon: Icon(FontAwesomeIcons.arrowLeft,
          //backgroundColor: Theme.of(context).primaryColor,
        ), onPressed: () => {
          Navigator.pop(context),}),
        title: Text('Setting'),

      ),
      body: Theme( data: Theme.of(context).copyWith(
        canvasColor: Theme.of(context).primaryColor, //This will change the drawer background to blue.),
        child: Center(
          child: Container(
            height: MediaQuery
                .of(context)
                .size
                .height - 60.0,
            child: ListView(
              scrollDirection: Axis.horizontal,
              children: <Widget>[
                Padding(
 padding: const EdgeInsets.only(top: 60.0),
                              child: RaisedButton(
                                  color:  Color(0xffffffff),

                                  child: Text('Notification time - $notifyTime',////NEED TO STORE LAST VALUE HERE////////
                                    style: TextStyle(
                                      color:  Color(0xff6200ee),
                                    ),),
                                  onPressed: () {
                                    DatePicker.showTimePicker(context, showTitleActions: true,
                                        onChanged: (date) {
                                          print('change $date');
                                        }, onConfirm: (date) {
                                          print('confirm $date');
                                          scheuleAtParticularTime(
                                              DateTime.fromMillisecondsSinceEpoch(
                                                  date.millisecondsSinceEpoch));
                                        }, currentTime: DateTime.now(), locale: LocaleType.en);
                                  },
                                  shape: RoundedRectangleBorder(
                                    borderRadius: BorderRadius.circular(
                                        30.0),)
                              ),
                            ),
 ],),


                ),
);
}
}

you can use the shared_preferences plugin to store data on the device and use it in the app, even after it restarts.

First import the shared preferences plugin:

import 'package:shared_preferences/shared_preferences.dart';

To store data, simply do:

SharedPreferences prefs = await SharedPreferences.getInstance();
bool storedSuccessfully = await prefs.setString('<Your_Key>', <Your_String_Value>);

To get the stored data:

SharedPreferences prefs = await SharedPreferences.getInstance();
String storedValue = prefs.getString('<YOUR-KEY>');

So in your case, every time a user selects the value, you just have to store it with a key, and then every time the app restarts, simply fetch that value using the key you gave it, and use it.