store and retrieve a class object in shared prefer

Question

In Android can we store an object of a class in shared preference and retrieve the object later?

If it is possible how to do it? If it is not possible what are the other possibilities of doing it?

I know that serialization is one option, but I am looking for possibilities using shared preference.

Answer 1

we can use Outputstream to output our Object to internal memory. And convert to string then save in preference. For example:

    mPrefs = getPreferences(MODE_PRIVATE);
    SharedPreferences.Editor ed = mPrefs.edit();
    ByteArrayOutputStream arrayOutputStream = new ByteArrayOutputStream();

    ObjectOutputStream objectOutput;
    try {
        objectOutput = new ObjectOutputStream(arrayOutputStream);
        objectOutput.writeObject(object);
        byte[] data = arrayOutputStream.toByteArray();
        objectOutput.close();
        arrayOutputStream.close();

        ByteArrayOutputStream out = new ByteArrayOutputStream();
        Base64OutputStream b64 = new Base64OutputStream(out, Base64.DEFAULT);
        b64.write(data);
        b64.close();
        out.close();

        ed.putString(key, new String(out.toByteArray()));

        ed.commit();
    } catch (IOException e) {
        e.printStackTrace();
    }

when we need to extract Object from Preference. Use the code as below

    byte[] bytes = mPrefs.getString(indexName, "{}").getBytes();
    if (bytes.length == 0) {
        return null;
    }
    ByteArrayInputStream byteArray = new ByteArrayInputStream(bytes);
    Base64InputStream base64InputStream = new Base64InputStream(byteArray, Base64.DEFAULT);
    ObjectInputStream in;
    in = new ObjectInputStream(base64InputStream);
    MyObject myObject = (MyObject) in.readObject();

Answer 2

There is no way to store objects in SharedPreferences, What i did is to create a public class, put all the parameters i need and create setters and getters, i was able to access my objects,

Answer 3

Using Gson Library:

dependencies {
compile 'com.google.code.gson:gson:2.8.2'
}

Store:

Gson gson = new Gson();
//Your json response object value store in json object
JSONObject jsonObject = response.getJSONObject();
//Convert json object to string
String json = gson.toJson(jsonObject);
//Store in the sharedpreference
getPrefs().setUserJson(json);

Retrieve:

String json = getPrefs().getUserJson();

Answer 4

You can do it using PowerPreference library in 3 easy steps!

https://github.com/AliEsaAssadi/Android-Power-Preference

1. Create Object

Object obj = new Object();

2. Write to shared preference

PowerPreference.defult().put("object",obj);

3. Getting the object

Object obj = PowerPreference.defult()
                               .getObject("object", Object.class);

Answer 5

You could use GSON, using Gradle Build.gradle :

implementation 'com.google.code.gson:gson:2.8.0'

Then in your code, for example pairs of string/boolean with Kotlin :

        val nestedData = HashMap<String,Boolean>()
        for (i in 0..29) {
            nestedData.put(i.toString(), true)
        }
        val gson = Gson()
        val jsonFromMap = gson.toJson(nestedData)

Adding to SharedPrefs :

        val sharedPrefEditor = context.getSharedPreferences(_prefName, Context.MODE_PRIVATE).edit()
        sharedPrefEditor.putString("sig_types", jsonFromMap)
        sharedPrefEditor.apply()

Now to retrieve data :

val gson = Gson()
val sharedPref: SharedPreferences = context.getSharedPreferences(_prefName, Context.MODE_PRIVATE)
val json = sharedPref.getString("sig_types", "false")
val type = object : TypeToken<Map<String, Boolean>>() {}.type
val map = gson.fromJson(json, type) as LinkedTreeMap<String,Boolean>
for (key in map.keys) {
     Log.i("myvalues", key.toString() + map.get(key).toString())
}

Answer 6

Do you need to retrieve the object even after the application shutting donw or just during it's running ?

You can store it into a database.
Or Simply create a custom Application class.

public class MyApplication extends Application {

    private static Object mMyObject;
    // static getter & setter
    ...
}

<manifest xmlns:android="http://schemas.android.com/apk/res/android">
    <application ... android:name=".MyApplication">
        <activity ... />
        ...
    </application>
    ...
</manifest>

And then from every activities do :

((MyApplication) getApplication).getMyObject();

Not really the best way but it works.