I already followed a few examples on YT and also an example on pub.dev and I still have a problem with saving the Switch value from false to true. Regarding documentation, it looks like everything is ok but still, it is not working. The question is what am I missing?

It is a very easy example with only this Switch. I wanted to check that in a simple way to learn it properly but it's not working. Can someone check the code and see what is going on?

It should Switch after a click from false to true and save it with shared preferences. After reloading or closing and running the app again it is still on false value.

import 'package:flutter/material.dart';
import 'package:shared_preferences/shared_preferences.dart';

void main() {
  runApp(
    MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const HomePage(),
    ),
  );
}

class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  State<HomePage> createState() => _HomePageState();
}

bool isChecked = false;

class _HomePageState extends State<HomePage> {
  @override
  void initState() {
    loadBool();
    super.initState();
  }

  loadBool() async {
    SharedPreferences preferences = await SharedPreferences.getInstance();
    isChecked = preferences.getBool('isChecked') ?? false;
  }

  @override
  Widget build(BuildContext context) {
    @override
    saveBool() async {
      SharedPreferences preferences = await SharedPreferences.getInstance();
      await preferences.setBool('isChecked', isChecked);
    }

    return Scaffold(
      appBar: AppBar(
        title: const Text('Home Page'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            const Text('Something'),
            Switch(
              value: isChecked,
              activeColor: Colors.green,
              onChanged: (value) {
                setState(() {
                  isChecked = value;
                });
                saveBool();
              },
            )
          ],
        ),
      ),
    );
  }
}

CodePudding user response：

i really encourage you to learn some state management way to get through this situations.

riverpod , bloc and provider are all some approaches for state management.

also learn how null safety works in flutter .

i have reproduced your problem and cam up with the following solution :

import 'package:flutter/material.dart';
import 'package:shared_preferences/shared_preferences.dart';

void main() {
  runApp(
    MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const HomePage(),
    ),
  );
}

class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  State<HomePage> createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  bool? isChecked;

  @override
  void initState() {
    loadBool();
    super.initState();
  }

  loadBool() async {
    SharedPreferences preferences = await SharedPreferences.getInstance();
    setState(() {
      isChecked = preferences.getBool('isChecked');
    });
  }

  @override
  Widget build(BuildContext context) {
    @override
    saveBool() async {
      SharedPreferences preferences = await SharedPreferences.getInstance();
      await preferences.setBool('isChecked', isChecked!);
      print(isChecked);
    }

    return Scaffold(
      appBar: AppBar(
        title: const Text('Home Page'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            const Text('Something'),
            Switch(
              value: isChecked!=null?isChecked!:false,
              activeColor: Colors.green,
              onChanged: (value) {
                setState(() {
                  isChecked = value;
                });
                saveBool();
              },
            )
          ],
        ),
      ),
    );
  }
}

CodePudding user response：

Try the following code:

import 'package:flutter/material.dart';
import 'package:shared_preferences/shared_preferences.dart';

void main() {
  runApp(
    MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const HomePage(),
    ),
  );
}

class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  State<HomePage> createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {

  bool isChecked = false;

  @override
  void initState() {
    loadBool();
    super.initState();
  }

  loadBool() async {
    SharedPreferences preferences = await SharedPreferences.getInstance();
    isChecked = preferences.getBool('isChecked') ?? false;
  }

  @override
  Widget build(BuildContext context) {
    @override
    saveBool() async {
      SharedPreferences preferences = await SharedPreferences.getInstance();
      await preferences.setBool('isChecked', isChecked);
    }

    return Scaffold(
      appBar: AppBar(
        title: const Text('Home Page'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            const Text('Something'),
            Switch(
              value: isChecked,
              activeColor: Colors.green,
              onChanged: (value) {
                setState(() {
                  isChecked = value;
                });
                saveBool();
              },
            )
          ],
        ),
      ),
    );
  }
}