ListToSharedPreferences.java

import android.content.Context;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.text.TextUtils;

import org.json.JSONArray;
import org.json.JSONException;

import java.util.ArrayList;
import java.util.List;


public class ListToSharedPreferences extends AppCompatActivity {
    private SharedPreferences prefs;

    private List<Integer> selectedIntegers = new ArrayList<>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        prefs = getSharedPreferences("myprefs", Context.MODE_PRIVATE);
    }


    @Override
    protected void onResume() {
        super.onResume();
        loadStateFromPrefs();
    }

    @Override
    protected void onPause() {
        super.onPause();
        storeStateToPrefs();
    }

    private void loadStateFromPrefs() {
        if (prefs == null) {
            return;
        }


        // read in json array from prefs to fill list
        selectedIntegers = new ArrayList<>();
        String jsonArrayString = prefs.getString("selectedIntegers", "");
        if (!TextUtils.isEmpty(jsonArrayString)) {
            try {
                JSONArray jsonArray = new JSONArray(jsonArrayString);
                if (jsonArray.length() > 0) {
                    for (int i = 0; i < jsonArray.length(); i++) {
                        Integer integer = jsonArray.getInt(i);
                        selectedIntegers.add(integer);
                    }
                }
            } catch (JSONException e) {
                e.printStackTrace();
            }
        }

    }

    protected void storeStateToPrefs() {
        if (prefs == null) {
            return;
        }
        SharedPreferences.Editor editor = prefs.edit();

        // store list as jsonarray
        JSONArray jsonArray = new JSONArray();
        for (Integer z : selectedIntegers) {
            jsonArray.put((int) z);
        }
        editor.putString("selectedIntegers", jsonArray.toString());
        editor.commit();
    }
}