Flutter shared_preferences not storing data

Question

I am trying to implement the package shared_preferences in my Flutter app.

I have included the package inside the pubspec.yaml file.

I have created a helper class called StorageUtil to manage shared_preferences in the project.

This is shared_preferences_util.dart:

import 'package:shared_preferences/shared_preferences.dart';

class StorageUtil {
  static StorageUtil _storageUtil;
  static SharedPreferences _preferences;

  static Future<StorageUtil> getInstance() async {
    if (_storageUtil == null) {
      // keep local instance till it is fully initialized.
      var secureStorage = StorageUtil._();
      await secureStorage._init();
      _storageUtil = secureStorage;
    }
    return _storageUtil;
  }

  StorageUtil._();
  Future _init() async {
    _preferences = await SharedPreferences.getInstance();
  }

  // get string
  static String getString(String key, {String defValue = ''}) {
    if (_preferences == null) return defValue;
    return _preferences.getString(key) ?? defValue;
  }

  // put string
  static Future<bool> putString(String key, String value) {
    if (_preferences == null) return null;
    return _preferences.setString(key, value);
  }
}

Then at file notification_service.dart I am creating an item inside shared_preferences:

  _refreshToken() {
    _firebaseMessaging.getToken().then((token) async {
      print('token: $token');
      StorageUtil.putString("token_firebase", token.toString());
      print('token despues de shared:' + token);
    }, onError: _tokenRefreshFailure);
  }

Print output:

I/flutter (29912): token despues ed shared:fy0Pk1asTOejYrWYXbULBu:APA91bGk2TLqdiLbGvZp7IrTggLfjwYcvhENB83RQj-7x1CEPoou_cY7Rq0eB6rFqEfb386pxSsWAogRc8HwQjK0Y9q9kyKgzSJ6ZCQ3qhFBIjaLhS2sZKJ-N1k7hdrRHdboyUb3WvGS

And later I am trying to get the shared_preferences item as follows:

final _tokenFb = StorageUtil.getString("token_firebase");

But it is always and empty String.

print("Token firebase en authbloc: " + _tokenFb);

Output:

I/flutter (29912): Token firebase en authbloc: 

What am I missing?

Answer 1

_preferences is null since you aren't calling await StorageUtil.getInstance() on your class. Therefore the _init method isn't called and SharedPreferences isn't being initialized.

You should call it like this:

  _refreshToken() {
    _firebaseMessaging.getToken().then((token) async {
      print('token: $token');
      var storageUtil = await StorageUtil.getInstance();
      storageUtil.putString("token_firebase", token.toString());
      print('token despues de shared:' + token);
    }, onError: _tokenRefreshFailure);
  }

And the same goes for StorageUtil.getString of course.