Persisting state of switch button with flutter/dart using shared preferences-CodePudding

I have a simple switch button and I'd like to persist the state of that button whenever I navigate to a new page and/or refresh the current page. I'm trying to use SharedPreferences to achieve this but haven't been successful.

Any help would be greatly appreciated!

Code:

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

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

  @override
  State<New> createState() => _NewState();
}

class _NewState extends State<New> {
  bool value = false;
  var selectFlag = 'false';

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

  Future<void> getValueFlag() async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    if (prefs.getString('selected_displayFlag') != null) {
      setState(() {
        selectFlag = prefs.getString('selected_displayFlag')!;
      });
    }
  }

  Future<void> setValueFlag(String valueFlag) async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    setState(() {
      selectFlag = valueFlag.toString();
      prefs.setString('selected_displayFlag', selectFlag);
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Switch(
        value: value,
        activeColor: Colors.black,
        onChanged: (valueFlag) {
          selectFlag == "false"
              ? setState(() {
                  selectFlag = "true";
                  value = true;
                  valueFlag = true;
                })
              : selectFlag == "true"
                  ? setState(() {
                      selectFlag = "false";
                      value = false;
                      valueFlag = false;
                    })
                  : null;
        },
      ),
    );
  }
}

CodePudding user response：

Switch(
        value: selectFlag,
        activeColor: Colors.black,
        onChanged: (valueFlag) {
          selectFlag == "false"
              ? setState(() {
                 setValueFlag(true);
                  selectFlag = "true";
                  value = true;
                  valueFlag = true;
                })
              : selectFlag == "true"
                  ? setState(() {
                      setValueFlag(false);
                      selectFlag = "false";
                      value = false;
                      valueFlag = false;
                    })
                  : null;
        },

and these methods should getBool and setBool

Future<void> getValueFlag() async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
   setState((){
    selectFlag = prefs.getBool('selected_displayFlag')?? true;
   });
  }

  Future<void> setValueFlag(Bool valueFlag) async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
      prefs.setBool('selected_displayFlag', valueFlag);
  }

In onchanged you missed to call the save method. And the value selectFlag wasnt assigned as the value to the switch

CodePudding user response：

This is what you need. https://biplabdutta.com.np/posts/theme-switching/

I recommend you go through this blog post of mine.