Android - save Object to SharedPreferences and get it anywhere in the app

Question

In my app I have a custom User class which holds some regular data (name etc...). I need to save that object and get it anywhere and anytime in other pages of the app. I made a helper class public final class GeneralMethods with many methods which I use a lot (static, of course).
In order to save the data Im using Gson library. I made this method:

public static void saveData(Context con, String variable, String data)
{
    SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(con);
    prefs.edit().putString(variable, data).apply();
}

To save an object, I use this method as follows:

Gson gson = new Gson();
String stringUser = gson.toJson(newUser);    
GeneralMethods.saveData(VerificationActivity.this,"userObject",stringUser);

To load the data back, I'm using this static method:

public static String getData(Context con, String variable, String defaultValue)
{
    SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(con);
    String data = prefs.getString(variable, defaultValue);
    return data;
}

I dont really know how to get the data back, this is what I've done so far:

Gson gson = new Gson();
String user="";
String value="";
user = GeneralMethods.getData(SplashScreenActivity.this,value,"userObject");

Im struggling with the getData method, how do I parse the data from String back to the User type?

EDIT
I tried the suggestions bellow and I always get NULL. Maybe I dont save the object in the right way?

EDIT2
It seems Im not generating the object correctly and therefore nothing is being saved. This is the user "Singleton" class:

public class User implements Serializable {

    private static User userInstance=null; //the only instance of the class
    private static String userName; //userName = the short phone number
    private User(){}

    public static User getInstance(){
        if(userInstance ==null){
            userInstance = new User();
        }
        return userInstance;
    }

    public static User getUserInstance() {
        return userInstance;
    }

    public String getUserName(){
        return this.userName;
    }

    public static void setUserName(String userName) {
        User.userName = userName;
    }

    public static void init(String _userName) {
        User.setUserName(_userName);
    }
}

This is how i setup the object with the relevant data (user name as the constructor parameter):

   User.init(name);

This is how i convert the object to a String:

   Gson gson = new Gson();
    String stringUser = gson.toJson(User.getInstance());
GeneralMethods.saveData(VerificationActivity.this,"userObject",stringUser);

Bad idea to use serialization for data storing. Use something for storing data. Realm for example. — Taxist Samael, Feb 28 '17 at 13:49

score 5 · Accepted Answer · 2015-04-02T12:44:11.313

Replace your existing User class with below

public class User implements Serializable
{

    private static User userInstance = null; // the only instance of the class
    private String userName; // userName = the short phone number
    private User(){}
    public static User getInstance()
    {
        if (userInstance == null)
        {
            userInstance = new User();
        }
        return userInstance;
    }

    public String getUserName()
    {
        return userName;
    }

    public void setUserName(String p_userName)
    {
        userName = p_userName;
    }

    @Override
    public String toString()
    {
        return "User [userName=" + getUserName() + "]";
    }
}

Initialize User Name

User m_user = User.getInstance();
m_user.setUserName(name);

Convert the object to a String

Gson gson = new Gson();
String stringUser = gson.toJson(m_user);
GeneralMethods.saveData(VerificationActivity.this,"userObject",stringUser);

Thanks, that worked as expected. Why did you have to remove the private constructor of the 'User' class? — Alex, Apr 02 '15 at 12:41
Why does it have to `implements Serializable` just to save in GSON? — IgorGanapolsky, Jun 16 '16 at 15:24

score 3 · Answer 2 · edited May 23 '17 at 12:17

I'd suggest you to use Dependency Injection pattern.

I usually create Preferences class which exposes getters and setters to quickly read and save values to SharedPreferences. I inject the same instance of Preferences anywhere in the code using Dagger as Dependency Injector.

Why use Singleton object over public static helpers?

If you have a helper class of utility functions that you're using directly, it creates a hidden dependency; you have no control over who can use it, or where. Injecting that same helper class via a stateless singleton instance lets you control where and how it's being used, and replace it / mock it / etc. when you need to.

Read more here.

Example of Preferences class:

@Singleton
public class Preferences {

    private SharedPreferences sharedPreferences;
    private final String NOTIFICATIONS_ENABLED = "NOTIFICATIONS_ENABLED";

    @Inject
    public Preferences(Context context) {
        sharedPreferences = context.getSharedPreferences("Preferences", 0);
    }

    public void setNotificationsEnabled(boolean enabled){
        SharedPreferences.Editor edit = sharedPreferences.edit();
        edit.putBoolean(NOTIFICATIONS_ENABLED, enabled);
        edit.commit();           
    }

    public boolean isNotificationsEnabled(){
        return sharedPreferences.getBoolean(NOTIFICATIONS_ENABLED, true);
    }
}

and how to use it in Activity:

public class MainActivity extends Activity {

    @Inject
    NavigationController navigationController;

    @Inject
    Preferences preferences;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        SharedObjectGraph.getObjectGraph().inject(this);

        if(preferences.isNotificationsEnabled()){
            // do something
        }
    }

score 2 · Answer 3 · answered Apr 02 '15 at 08:30

2

You need to just replace one line of code

user = GeneralMethods.getData(SplashScreenActivity.this,value,"userObject");

To

user = GeneralMethods.getData(SplashScreenActivity.this,"userObject",value);

answered Apr 02 '15 at 08:30

I tried what you've suggested and it seems something else is broken. When I create a new user and save it, when I try to get the user's name, i get NULL. Maybe i dont save the object correctly? – Alex Apr 02 '15 at 09:23
Did you get string from "String stringUser = gson.toJson(newUser);" this line I checked your code & working fine. – Apr 02 '15 at 09:33
Apparently not, i get only `{ }`. Probably not creating the object correctly. Im using a Singleton as the base `User` class. I will update my question with the relevant data. – Alex Apr 02 '15 at 09:46

score 0 · Answer 4 · answered Apr 02 '15 at 07:07

For getting the data back-

//Creating a shared preference
SharedPreferences  mPrefs = getPreferences(MODE_PRIVATE);

Gson gson = new Gson();
    String json = mPrefs.getString("MyObject", "");
    MyObject obj = gson.fromJson(json, MyObject.class);

Hope this helps :)

John · Answer 5 · 2015-04-02T08:26:34.817

0

public static String getData(Context con, String variable)
{
SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(con);
String data = prefs.getString(variable, null);
return data;
}

Gson gson = new Gson();
String json = GeneralMethods.getData(SplashScreenActivity.this,"userObject");
if(json!=null){
  MyObject obj = gson.fromJson(json, MyObject.class);
}

edited Apr 02 '15 at 08:26

answered Apr 02 '15 at 07:16

John

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What is `GeneralMethods`? – IgorGanapolsky May 28 '20 at 17:04

score 0 · Answer 6 · answered Apr 02 '15 at 07:23

You are doing it correctly, but i think you have switched the two fields in the getData method.

You have this method:

public static String getData(Context con, String variable, String defaultValue)
{....}

But you are sending in this:

user = GeneralMethods.getData(SplashScreenActivity.this,value,"userObject");

That means that your variable is this.value and your defaultValue is "userObject". I believe you want to have it the other way around

score 0 · Answer 7 · edited Jun 20 '20 at 09:12

Try this

This will help you to create a class of shared preference and use it any where in any class.

Create a class named as MySharedPreferences

public class MySharedPreferences
{
 public static final String mySharedPrefrences = "MyPrefs" ;
 public static SharedPreferences sharedPreferences;
 public static SharedPreferences.Editor editor;
  private static MySharedPreferences instance;

public static MySharedPreferences with(Context context) {
if (instance == null) {
    instance = new MySharedPreferences(context);
}
return instance;
}

public MySharedPreferences(Context context)
{
sharedPreferences=context.getSharedPreferences(mySharedPrefrences, Context.MODE_PRIVATE);
}

public static String  getUserId(String str_userid)
{
if (sharedPreferences!= null) {
    return sharedPreferences.getString(str_userid, "");
}
return "";
}

public void saveUserId(String str_userId_key,String str_userId_value)
{
editor = sharedPreferences.edit();
editor.putString(str_userId_key,str_userId_value);
editor.commit();
}

public void clearAllData(Context context)
{
sharedPreferences = context.getSharedPreferences(mySharedPrefrences, Context.MODE_PRIVATE);
SharedPreferences.Editor editor = sharedPreferences.edit();
editor.clear().apply();
}
}

And use this like

MySharedPreferences yourPrefrence =MySharedPreferences.with(getActivity());yourPrefrence.saveUserId("str_userId_key",et_title.getText().toString().trim());
String value = yourPrefrence.getUserId("str_userId_key");

Android - save Object to SharedPreferences and get it anywhere in the app

7 Answers7

Try this

Linked