Flutter SharedPreferences getBool function returns null

Question

I have the class below which I set and get the bool value to remember the user and auto-login next time.

import 'package:shared_preferences/shared_preferences.dart';

class SettingHelper {
  static Future<bool> getValue(String key) async {
    final SharedPreferences prefs = await SharedPreferences.getInstance();
    var s = prefs.getBool(key);
    print("GetValue ${s.toString()}"); //prints "GetValue true"
    return s;
  }

  static Future<void> setValue(String key, bool value) async {
    final SharedPreferences prefs = await SharedPreferences.getInstance();
    prefs.setBool(key, value);
  }
}

I set my value in Login page with a CheckBox value.

onPressed: () {
...
SettingHelper.setValue("rememberMe", checkBoxValue);
...
}

When I start debugging I saw setValue worked. But when I hot restart getValue returns null in initState() but returns true in function. Here is the code:

class LandingPage extends StatefulWidget {
  @override
  _LandingPageState createState() => _LandingPageState();
}

class _LandingPageState extends State<LandingPage> {
  bool rememberMe;

  void _getRememberMeChoice() async {
    rememberMe = await SettingHelper.getValue("rememberMe");
  }

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

  @override
  Widget build(BuildContext context) {
    print(rememberMe);  //Returns null
    if (rememberMe == true) {
      return BridgeList();
    } else
      return LoginScreen();
  }
}

These are the outputs:

I/flutter (11724): null
I/flutter (11724): GetValue true

Please tell me if I'm doing something wrong...

Sebastian · Accepted Answer · 2020-06-04 14:50:12Z

0

That's because you can't await a value inside initState()

In this case the build() function is executed before you get the rememberMe value.

Try adding a setState((){}) after the getValue(), so you do a rebuild.

Like this

void _getRememberMeChoice() async {
    rememberMe = await SettingHelper.getValue("rememberMe");
    setState((){})
  }

Also, notice that in the first build execution, the rememberMe value will be null. So you should add that validation in your if condition.

edited Jun 4, 2020 at 14:50

answered Jun 4, 2020 at 14:44

Sebastian

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