Flutter: I want to create a global variant. After close the app, it can be saved for the next time I open the app again - flutter

Question

import 'package:flutter/material.dart';
import 'package:shared_preferences/shared_preferences.dart';
class Global {
static SharedPreferences _prefs;
static String key;
static Future init() async {
WidgetsFlutterBinding.ensureInitialized();
_prefs = await SharedPreferences.getInstance();
var _key = _prefs.getString("key");
if (_key != null) {
key = _key;
}
}
static saveKey(value) => _prefs.setString("key", value);
}
Here I create a global class. And I set and get value by this way.
Global.key = value; //set
Global.key; //get
But after I close the app, the value is gone. Any suggestions?

Answer 1

import 'package:flutter/material.dart';
import 'package:shared_preferences/shared_preferences.dart';
class Global {
static SharedPreferences _prefs;
static String key;
String get init => key; // adding a getter
static Future init() async {
WidgetsFlutterBinding.ensureInitialized();
_prefs = await SharedPreferences.getInstance();
var _key = _prefs.getString("key");
if (_key != null) {
key = _key;
}
}
static saveKey(value) => _prefs.setString("key", value);
}
Global().init =value; or Global.init = value; //set
Global().init; //get Global.init; //get

Answer 2

Are you ever calling your Init function in your Main method?
void main() async {
await Global.init();
runApp(MyApp());
}
Assuming you're doing that, the other mistake here is how you're trying to store your value. Use the saveKey function you have in place that's what it's there for. Throw this on one of your pages.
ElevatedButton(
onPressed: () {
Global.saveKey('Test');
},
child: Text('Test'),
),
Your Global class was perfectly fine, its how you were trying to use it. Try this though, only change is that I included a null check so you don't have to create an extra variable that's not used. Also added a print statement that will print the stored value when you re-start the app. It all works fine on my end.
class Global {
static SharedPreferences _prefs;
static String key;
static Future init() async {
WidgetsFlutterBinding.ensureInitialized();
_prefs = await SharedPreferences.getInstance();
key = _prefs.getString('key') ?? ''; // null check here
debugPrint(key);
}
static saveKey(value) => _prefs.setString("key", value);
}