[shared_preferences] cast exception with get/setStringList: type 'List<Object?>' is not a subtype of type 'List?'

Steps to reproduce

[ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: type 'List<Object?>' is not a subtype of type 'List?' in type cast

Expected results

setStringList is not working properly

Actual results

Should be a List<String>, not List<Object>

Code sample

final SharedPreferencesWithCache prefsWithCache =
    await SharedPreferencesWithCache.create(
  cacheOptions: const SharedPreferencesWithCacheOptions(
    // When an allowlist is included, any keys that aren't included cannot be used.
    allowList: <String>{'action'},
  ),
);

await prefsWithCache!.setStringList('action', <String>['Earth', 'Moon', 'Sun']);

Screenshots or Video

Screenshots / Video demonstration

[Upload media here]

Logs

[Paste your logs here]

Flutter Doctor output

Doctor output

[Paste your output here]

works for me

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

final class SharedPreferencesKeys {
  static const action = 'action';
}

void main() async {
  final prefsWithCache = await SharedPreferencesWithCache.create(
    cacheOptions: const SharedPreferencesWithCacheOptions(
      allowList: {SharedPreferencesKeys.action},
    ),
  );

  await prefsWithCache.setStringList(
    SharedPreferencesKeys.action,
    const ['Earth', 'Moon', 'Sun'],
  );

  final actions =
      prefsWithCache.getStringList(SharedPreferencesKeys.action) ?? [];

  runApp(
    MaterialApp(
      home: Material(
        child: Column(
          children: [
            for (final action in actions) Text(action),
          ],
        ),
      ),
    ),
  );
}

[!] Flutter (Channel stable, 3.22.3, on macOS 14.5 23F79 darwin-arm64, locale en-US)
    ! Warning: `dart` on your path resolves to /opt/homebrew/Cellar/dart/3.4.4/libexec/bin/dart, which is not inside your current Flutter SDK checkout at
      /Users/francesco/fvm/versions/stable. Consider adding /Users/francesco/fvm/versions/stable/bin to the front of your path.
[✓] Android toolchain - develop for Android devices (Android SDK version 34.0.0)
[✓] Xcode - develop for iOS and macOS (Xcode 15.4)
[✓] Chrome - develop for the web
[✓] Android Studio (version 2022.3)
[✓] VS Code (version 1.91.1)
[✓] Connected device (3 available)
[✓] Network resources

name: issue_152607
description: "A new Flutter project."
publish_to: 'none'
version: 1.0.0+1

environment:
  sdk: '>=3.4.4 <4.0.0'

dependencies:
  flutter:
    sdk: flutter
  shared_preferences: ^2.3.0

dev_dependencies:
  flutter_test:
    sdk: flutter
  flutter_lints: ^3.0.0

flutter:
  uses-material-design: true

is this required?
final class SharedPreferencesKeys {
static const action = 'action';
}

The docs says just using the string as the key is fine

is this required? final class SharedPreferencesKeys { static const action = 'action'; }

The docs says just using the string as the key is fine

is not required, this is just me avoiding hard-coding the string 'action' all over the place
you can delete it and replace SharedPreferencesKeys.action with 'action' if you like it better

does the code run on your device?

also, you don't need "!" here

await prefsWithCache!.setStringList

I have a global variable of:
SharedPreferencesWithCache? prefsWithCache;

In a separate file outside of main, im doing this:
await prefsWithCache!.setStringList('ingredients', ['cherry', 'diamond']);

this is causing this error:
[ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: type 'List<Object?>' is not a subtype of type 'List?' in type cast
#0 SharedPreferencesWithCache.getStringList (package:shared_preferences/src/shared_preferences_async.dart:310:44)

I think it has somethign to do when prefsWithCache is used outside of main? I cant seem to setStringList when its outside of main, it keeps complaining of List<Object?>, no issue when doing setString outside of main

@OverRide

eg something like this:

void main() async {
await WidgetsFlutterBinding.ensureInitialized();
prefsWithCache = await SharedPreferencesWithCache.create(
cacheOptions: const SharedPreferencesWithCacheOptions(),
);
// await prefsWithCache!.clear();

List? savedIngredients = prefsWithCache!.getStringList('ingredients');

print("ingredients");
// await prefsWithCache!.setStringList('ingredients', ['cherry', 'diamond']);
print(savedIngredients);

runApp(ChangeNotifierProvider(
create: (context) => IngredientsState()..updateState(savedIngredients ?? []), child: const MainApp()));
}

class MainApp extends StatelessWidget {
const MainApp({super.key});

@OverRide
Widget build(BuildContext context) {
prefsWithCache!.setStringList('ingredients', ['cherry', 'diamond']);
screenWidth = MediaQuery.of(context).size.width;
screenWidthRatio = screenWidth / prototypeWidth;
screenHeight = MediaQuery.of(context).size.height;
screenHeightRatio = screenHeight / prototypeHeight;

return MaterialApp(
  navigatorObservers: [routeObserver],
  debugShowCheckedModeBanner: false,
  onGenerateRoute: generateRoute,
);

}
}

I have a global variable of:

please don't do that,
if you really really want something similar to a global variable you can use a singleton

singleton example

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

final class SharedPreferencesKeys {
  static const action = 'action';
}

class SharedPreferencesSingleton {
  SharedPreferencesSingleton._internal();

  factory SharedPreferencesSingleton() => _instance;
  static final _instance = SharedPreferencesSingleton._internal();
  SharedPreferencesWithCache? _prefsWithCache;

  /// you have to remember to call `initialize()`
  Future<void> initialize({Set<String>? allowList}) async {
    _prefsWithCache ??= await SharedPreferencesWithCache.create(
      cacheOptions: SharedPreferencesWithCacheOptions(
        allowList: allowList,
      ),
    );
  }

  /// you have to remember to call `dispose()`
  void dispose() {
    _prefsWithCache = null;
  }

  SharedPreferencesWithCache get prefsWithCache =>
      _prefsWithCache ??
      () {
        throw Exception('you forgot to initialize');
      }();
}

void main() async {
  await SharedPreferencesSingleton().initialize(
    allowList: {SharedPreferencesKeys.action},
  );

  await SharedPreferencesSingleton().prefsWithCache.setStringList(
    SharedPreferencesKeys.action,
    const ['Earth', 'Moon', 'Sun'],
  );

  runApp(const MyApp());
}

class MyApp extends StatefulWidget {
  const MyApp({super.key});

  @override
  State<MyApp> createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  @override
  void dispose() {
    SharedPreferencesSingleton().dispose();
    super.dispose();
  }

  @override
  Widget build(context) => const MaterialApp(home: MyHomePage());
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key});

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(context) {
    final actions = SharedPreferencesSingleton()
            .prefsWithCache
            .getStringList(SharedPreferencesKeys.action) ??
        [];
    return Material(
      child: Column(
        children: [
          for (final action in actions) Text(action),
        ],
      ),
    );
  }
}

but what you might actually need is a state management
I can recommend riverpod.dev

id like for my variables to be stored locally, so when user starts app again the data is stored again. and throughout the app the user can write to shared preferences. im already using providers for state management

I think this is more a discussion on best practices rather than an issue with flutter,
maybe it's better to close the issue and discuss it on discord

@itismejy

@itismejy
Check the plugin example to see if it helps in your case or not.
Also check if this helps.

@itismejy

@itismejy Please provide a complete reproducible test case that someone can run to see the issue; so far you've only provided fragments that don't compile in isolation, and the description of the error are too vague to be able to investigate (e.g., this comment only shows one line of code and says it causes an exception, but the line of code is a set call and the exception described can only come from get, so there are clearly missing steps there.)

Also, please indicate which platform you are running on, as it may be platform-implementation-specific.

@iapicca

I think this is more a discussion on best practices rather than an issue with flutter,
maybe it's better to close the issue and discuss it on discord

@iapicca Please do not discourage people from reporting exceptions. Whether shared_preferences is the subjectively best tool for the use case, or whether globals are good or bad, is not material to the issue here. If a valid sequence of calls to the shared_preferences API can cause a cast exception, then there's a bug in shared_preferences.

@iapicca

I have a global variable of: SharedPreferencesWithCache? prefsWithCache;

In a separate file outside of main, im doing this: await prefsWithCache!.setStringList('ingredients', ['cherry', 'diamond']);

this is causing this error: [ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: type 'List<Object?> > > ' is not a subtype of type 'List?' in type cast #0 SharedPreferencesWithCache.getStringList (package:shared_preferences/src/shared_preferences_async.dart:310:44)
[...]
I think it has somethign to do when prefsWithCache is used outside of main? I cant seem to setStringList when its outside of main, it keeps complaining of List<Object?>, no issue when doing setString outside of main

I think this is more a discussion on best practices rather than an issue with flutter,
maybe it's better to close the issue and discuss it on discord

@iapicca Please do not discourage people from reporting exceptions. Whether shared_preferences is the subjectively best tool for the use case, or whether globals are good or bad, is not material to the issue here. If a valid sequence of calls to the shared_preferences API can cause a cast exception, then there's a bug in shared_preferences.

@stuartmorgan
my bad I thought the reporter (by his/her words [1, 2]) identified the issue in being caused by the use of the package

Thanks guys for your work!

[shared_preferences] fix stringlist bug (flutter#7268)

This thread has been automatically locked since there has not been any recent activity after it was closed. If you are still experiencing a similar issue, please open a new bug, including the output of flutter doctor -v and a minimal reproduction of the issue.

[shared_preferences] fix stringlist bug (flutter#7268)

Navigation Menu

Repository navigation

[shared_preferences] cast exception with get/setStringList: `type 'List<Object?>' is not a subtype of type 'List?'` #152607

Steps to reproduce

Expected results

Actual results

Code sample

Screenshots or Video

Logs

Flutter Doctor output

4 remaining items

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

[shared_preferences] cast exception with get/setStringList: type 'List<Object?>' is not a subtype of type 'List?' #152607

Description

Steps to reproduce

Expected results

Actual results

Code sample

Screenshots or Video

Logs

Flutter Doctor output

Activity

iapicca commented on Jul 31, 2024

itismejy commented on Jul 31, 2024

iapicca commented on Jul 31, 2024

itismejy commented on Jul 31, 2024

itismejy commented on Jul 31, 2024

itismejy commented on Jul 31, 2024

iapicca commented on Jul 31, 2024

itismejy commented on Jul 31, 2024

iapicca commented on Jul 31, 2024

darshankawar commented on Jul 31, 2024

stuartmorgan-g commented on Jul 31, 2024

stuartmorgan-g commented on Jul 31, 2024

4 remaining items

iapicca commented on Jul 31, 2024

itismejy commented on Aug 1, 2024

github-actions commented on Aug 16, 2024

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Issue actions

[shared_preferences] cast exception with get/setStringList: `type 'List<Object?>' is not a subtype of type 'List?'` #152607