Android ArrayList of custom objects - Save to SharedPreferences - Serializable?

Question

I have an ArrayList of an object. The object contains the types 'Bitmap' and 'String' and then just getters and setters for both. First of all is Bitmap serializable?

How would I go about serializing this to store it in SharedPreferences? I have seen many people ask a similar question but none seem to give a good answer. I would prefer some code examples if at all possible.

If bitmap is not serializable then how do I go about storing this ArrayList?

Answer 1

Yes, you can save your composite object in shared preferences. Let's say..

 Student mStudentObject = new Student();
 SharedPreferences appSharedPrefs = PreferenceManager
             .getDefaultSharedPreferences(this.getApplicationContext());
 Editor prefsEditor = appSharedPrefs.edit();
 Gson gson = new Gson();
 String json = gson.toJson(mStudentObject);
 prefsEditor.putString("MyObject", json);
 prefsEditor.commit(); 

..and now you can retrieve your object as:

 SharedPreferences appSharedPrefs = PreferenceManager
             .getDefaultSharedPreferences(this.getApplicationContext());
 Gson gson = new Gson();
 String json = appSharedPrefs.getString("MyObject", "");
 Student mStudentObject = gson.fromJson(json, Student.class);

For more information, click here.

If you want to get back an ArrayList of any type object e.g. Student, then use:

Type type = new TypeToken<List<Student>>(){}.getType();
List<Student> students = gson.fromJson(json, type);

Answer 2

The answer above works, but not for list:

For saving list of objects do like this:

List<Cars> cars= new ArrayList<Cars>();
    cars.add(a);
    cars.add(b);
    cars.add(c);
    cars.add(d);

    gson = new Gson();
    String jsonCars = gson.toJson(cars);
    Log.d("TAG","jsonCars = " + jsonCars);

Read the json object:

Type type = new TypeToken<List<Cars>>(){}.getType();
List<Cars> carsList = gson.fromJson(jsonCars, type);

Answer 3

For me it worked like this :

Put values in SharedPreferances :

String key = "Key";
ArrayList<ModelClass> ModelArrayList=new ArrayList();

SharedPreferences shref;
SharedPreferences.Editor editor;
shref = context.getSharedPreferences(MyPREFERENCES, Context.MODE_PRIVATE);

Gson gson = new Gson();
String json = gson.toJson(ModelArrayList);

editor = shref.edit();
editor.remove(key).commit();
editor.putString(key, json);
editor.commit();

To get values from SharedPreferances :

Gson gson = new Gson();
String response=shref.getString(key , "");
ArrayList<ModelClass> lstArrayList = gson.fromJson(response, 
    new TypeToken<List<ModelClass>>(){}.getType());

Answer 4

For Save:

public static void saveSharedPreferencesLogList(Context context, List<PhoneCallLog> callLog) {
    SharedPreferences mPrefs = context.getSharedPreferences(Constant.CALL_HISTORY_RC, context.MODE_PRIVATE);
    SharedPreferences.Editor prefsEditor = mPrefs.edit();
    Gson gson = new Gson();
    String json = gson.toJson(callLog);
    prefsEditor.putString("myJson", json);
    prefsEditor.commit();
}

For load:

public static List<PhoneCallLog> loadSharedPreferencesLogList(Context context) {
    List<PhoneCallLog> callLog = new ArrayList<PhoneCallLog>();
    SharedPreferences mPrefs = context.getSharedPreferences(Constant.CALL_HISTORY_RC, context.MODE_PRIVATE);
    Gson gson = new Gson();
    String json = mPrefs.getString("myJson", "");
    if (json.isEmpty()) {
        callLog = new ArrayList<PhoneCallLog>();
    } else {
        Type type = new TypeToken<List<PhoneCallLog>>() {
        }.getType();
        callLog = gson.fromJson(json, type);
    }
    return callLog;
}

PhoneCallLog is my custom object's name. (Contains String, long and boolean values)

Answer 5

Mete' example above worked like a charm.
Here is a Kotlin example

private var prefs: SharedPreferences = context?.getSharedPreferences("sharedPrefs", MODE_PRIVATE)
    ?: error("err")
private val gson = Gson()

save

fun saveObjectToArrayList(yourObject: YourObject) {
    val bookmarks = fetchArrayList()
    bookmarks.add(0, yourObject)
    val prefsEditor = prefs.edit()

    val json = gson.toJson(bookmarks)
    prefsEditor.putString("your_key", json)
    prefsEditor.apply()
}

read

fun fetchArrayList(): ArrayList<YourObject> {
    val yourArrayList: ArrayList<YourObject>
    val json = prefs.getString("your_key", "")

    yourArrayList = when {
        json.isNullOrEmpty() -> ArrayList()
        else -> gson.fromJson(json, object : TypeToken<List<Feed>>() {}.type)
    }

    return yourArrayList
}

Answer 6

solution

Don't worry you can follow my code.I am using own custom class of sharedPreference for holding anytype of List in sharedPreference.

public class AuthPreference {
    private static final String MY_PREFERENCES = "MY_PREFERENCES";
    private static final int MODE = Context.MODE_PRIVATE;
    private static AuthPreference pref;
    private final SharedPreferences sharedPreference;
    private final SharedPreferences.Editor editor;

    @SuppressLint("CommitPrefEdits")
    public AuthPreference(Context context) {
        sharedPreference = context.getSharedPreferences(MY_PREFERENCES, MODE);
        editor = sharedPreference.edit();
    }

    public void clear() {
        editor.clear().commit();

    }

    //Here  save your api responce like YourModel arraylist

    public void saveDataResponce(ArrayList<YourModel> model_, String key) {
        SharedPreferences.Editor editor = sharedPreference.edit();
        Gson gson = new Gson();
        String json = gson.toJson(model_);
        editor.putString(key, json);
        editor.apply();
    }

//Here we get our api responce like YourModel arraylist.Using key value when you want to define.

    public ArrayList<YourModel> getDataResponce(String key) {
        Gson gson = new Gson();
        String json = sharedPreference.getString(key, null);
        Type type_ = new TypeToken<ArrayList<YourModel>>() {
        }.getType();
        return gson.fromJson(json, type_);
    }
}

Answer 7

The kotlin implementation with Gson, extending @SpyZips's answer,

Serializing to JSON

val jsonCars: String = Gson().toJson(cars);

Deserializing to back to list of objs

val type = object: TypeToken<List<Car>>(){}.type
val carsList: List<Car> = Gson().fromJson(jsonCars, type)