How to store ArrayList of my class in shared preference?

Question

I want to store ArrayList of Polygon objects in shared preference. Can someone help me with this?

To save list:

public void savePolygonObjects(Context context){
    SharedPreferences mPrefs = context.getSharedPreferences("MyPref", context.MODE_PRIVATE);
    SharedPreferences.Editor prefsEditor = mPrefs.edit();
    Gson gson = new Gson();
    String json = gson.toJson(polygonArrayList);
    prefsEditor.putString("myJson", json);
    prefsEditor.commit();
}

To retrieve list:

SharedPreferences mPrefs = getSharedPreferences("MyPref", 
                                     getApplicationContext().MODE_PRIVATE);
Gson gson = new Gson();
String json = mPrefs.getString("myJson", "");
JsonParser parser = new JsonParser();
JsonArray array = parser.parse(json).getAsJsonArray();

for(int i=0; i< array.size(); i++){
    polygonArrayList.add(gson.fromJson(array.get(i), Polygon.class));
}

the only way is to convert your array into a JSON string and save it in shared prefs. — Luca Nicoletti, Jul 03 '18 at 13:18
it gives me error : java.lang.IllegalArgumentException: class gs declares multiple JSON fields named d @LucaNicoletti — Bhushan Borole, Jul 03 '18 at 13:45
The above code gives me exception saying that cannot convert object to json. it gives error at gson.toJson(list) @LucaNicoletti — Bhushan Borole, Jul 05 '18 at 02:20
you have to register type adapter in the Gson object, follow the guide [here](https://github.com/google/gson/blob/master/UserGuide.md) — Luca Nicoletti, Jul 05 '18 at 07:18
It is still giving me error at the same line, i guess it is not converting to json for some reason @LucaNicoletti — Bhushan Borole, Jul 05 '18 at 12:25
see i updated @LucaNicoletti, i just want to store ArrayList of Polygons in shared preference, Polygons which are objects of google maps. — Bhushan Borole, Jul 05 '18 at 16:31
Can you post more code? The class, where you create that `polygonArrayList` and by the way, you're not using Gson to retrieve the data, you use it only to save the data — Luca Nicoletti, Jul 06 '18 at 07:11
I am using gson to retrieve, see inside the for loop @LucaNicoletti, polygonArrayList is just a collection in which i add Polygon objects when a polygon's color is changed — Bhushan Borole, Jul 06 '18 at 09:34
The code does not compile, do you have any other way other than gson and json? @LucaNicoletti — Bhushan Borole, Jul 08 '18 at 05:15
No, just follow step by step the tutorial I gave, and use the same classes — Luca Nicoletti, Jul 08 '18 at 06:22
Do you have a different example which is a little precise to my subject? @LucaNicoletti — Bhushan Borole, Jul 09 '18 at 16:09

score 0 · Answer 1 · answered Jul 04 '18 at 02:39

You can add your ArrayList as serialized object to the SharedPreferences and later deserialize it while reading it from the SharedPreferences. Here's a code sample for that:

ArrayList<Polygon> polygonList = new ArrayList<Polygon>();

// Add the data to the list

// Serializing and adding the ArrayList to the SharedPreferences
SharedPreferences prefs = getSharedPreferences(SHARED_PREF_NAME, Context.MODE_PRIVATE);
  Editor editor = prefs.edit();
  try {
    editor.putString(POLYGONS, ObjectSerializer.serialize(polygonList));
  } catch (IOException e) {
    e.printStackTrace();
  }
  editor.commit();

Then later retrieve the ArrayList by deserializing it as follows:

 SharedPreferences prefs = getSharedPreferences(SHARED_PREF_NAME, Context.MODE_PRIVATE);

  try {
    polygonList = (ArrayList<POLYGON>) ObjectSerializer.deserialize(prefs.getString(POLYGONS, ObjectSerializer.serialize(new ArrayList<POLYGON>())));
  } catch (IOException e) {
    e.printStackTrace();
  } catch (ClassNotFoundException e) {
    e.printStackTrace();
  }

You need to add the ObjectSerializer class to your project too, you can get it from here: ObjectSerializer.java

I referred this answer, and there is an alternate method too for this so you can check that out too

which dependencies should i add for org.apache.pig? @Sudhanshu Vohra — Bhushan Borole, Jul 04 '18 at 06:34
@BhushanBorole copy the class to your project and that will do, Note: remove the dependencies: import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; and private static final Log log = LogFactory.getLog(ObjectSerializer.class); as they are not important. Also update the package name too. — Sudhanshu Vohra, Jul 04 '18 at 06:46
I did all the stuff, but still its not working, there is no exception, but still i am not getting the required data. @Sudhanshu Vohra — Bhushan Borole, Jul 05 '18 at 02:20
Is that returning "null" when you fetch it from SharedPreferences ? — Sudhanshu Vohra, Jul 05 '18 at 02:22

score -5 · Answer 2 · answered Jul 03 '18 at 13:19

-5

List<Person> customer = new ArrayList<Person>();
Person p = .....;
customer.add(person);

answered Jul 03 '18 at 13:19

Siru malayil

197
2
11

How to store ArrayList of my class in shared preference?

2 Answers2