How to delete data of shared-preferences from singleton in flutter? - flutter

Question

I make one file to shared preferences to store data in it from my app. It's work fine.But now I want to delete data from store as button log-out for user. So if user click button of log-out data will be clear from shared preferences file. How I can do it from different class?
import 'package:shared_preferences/shared_preferences.dart';
class MyPreferences{
static const USER = "user";
static const PASSWORD = "password";
static final MyPreferences instance = MyPreferences._internal();
//Campos a manejar
SharedPreferences _sharedPreferences;
String user = "";
String password = "";
MyPreferences._internal(){
}
factory MyPreferences()=>instance;
Future<SharedPreferences> get preferences async{
if(_sharedPreferences != null){
return _sharedPreferences;
}else{
_sharedPreferences = await SharedPreferences.getInstance();
user = _sharedPreferences.getString(USER);
password = _sharedPreferences.getString(PASSWORD);
return _sharedPreferences;
}
}
Future<bool> commit() async {
await _sharedPreferences.setString(USER, user);
await _sharedPreferences.setString(PASSWORD, password);
}
Future<MyPreferences> init() async{
_sharedPreferences = await preferences;
return this;
}
}

Answer 1

Define your shared preference manager class as a singleton as given,
class SharedPreferenceManager{
static final SharedPreferenceManager _singleton = new SharedPreferenceManager._internal();
factory SharedPreferenceManager() {
return _singleton;
}
SharedPreferenceManager._internal() {
... // initialization logic here
}
... // rest of the class
}
By this, you can create and access the single, reusable instance of that class. You can define a static method in the class which will be accessible from outside. As the static method can have access to only static data members, You should define the sharedPrefernece member variable as static. Here is how you can clear all the data.
static Future<bool> clearSharedPrefs(){
SharedPreferences preferences = await SharedPreferences.getInstance();
await preferences.clear();
}
After this, you'll be able to call this method from any class, just as SharedPreferenceManager.clearSharedPrefs().
It's a good practice to follow the singleton pattern for database, network and shared preference related tasks.
Here is the code you should go with.
import 'package:shared_preferences/shared_preferences.dart';
class MyPreferences{
static const USER = "user";
static const PASSWORD = "password";
static final MyPreferences instance = MyPreferences._internal();
static SharedPreferences _sharedPreferences;
String user = "";
String password = "";
MyPreferences._internal(){}
factory MyPreferences()=>instance;
Future<SharedPreferences> get preferences async{
if(_sharedPreferences != null){
return _sharedPreferences;
}else{
_sharedPreferences = await SharedPreferences.getInstance();
user = _sharedPreferences.getString(USER);
password = _sharedPreferences.getString(PASSWORD);
return _sharedPreferences;
}
}
Future<bool> commit() async {
await _sharedPreferences.setString(USER, user);
await _sharedPreferences.setString(PASSWORD, password);
}
Future<MyPreferences> init() async{
_sharedPreferences = await preferences;
return this;
}
static Future<bool> clearPreference() async{
if(_sharedPreferences){
_sharedPreferences.clear();
}
}
}

Answer 2

You can use remove or clear on shared preferences.
SharedPreferences preferences = await SharedPreferences.getInstance();
preferences.clear();
// OR
preferences.remove("MY KEY HERE");