Android - how to add JSON object to sharedPreferences?

Question

I would like to append data into existing JSON object and save data as string into shared preferences with following structure.

"results":[
          {
             "lat":"value",
             "lon":"value"
          }, 
          {
             "lat":"value",
             "lon":"value"

          }
        ]

How can i do it right?

I tried something like this, but without luck.

// get stored JSON object with saved positions
String jsonDataString = this.getSharedPreferencesStringValue(ctx, "positions", "last_positions");

if (jsonDataString != null) {
    Log.i(AppHelper.APP_LOG_NAMESPACE, "JSON DATA " + jsonDataString);
    JSONObject jsonData = new JSONObject(jsonDataString);
    jsonData.put("lat", lat.toString());
    jsonData.put("lon", lon.toString());
    jsonData.put("city", city);
    jsonData.put("street", street);
    jsonData.put("date", appHelper.getActualDateTime());
    jsonData.put("time", appHelper.getActualDateTime());
    this.setSharedPreferencesStringValue(ctx, "positions", "last_positions", jsonData.toString());
} else {
    this.setSharedPreferencesStringValue(ctx, "positions", "last_positions","{}");                  
}

Thanks for any advice.

For What you are saving complete JSON object in SharedPreferences ? — Mick
– Mick, Commented May 18, 2014 at 0:04
Question is about creating JSON structure. not about purpose of saving JSON string in shared prefs. I think that is it more simplest solution that work with SQL in Android. — redrom
– redrom, Commented May 18, 2014 at 6:30
I want to append new object to old object, to get JSON structure like in my question. — redrom
– redrom, Commented May 18, 2014 at 9:23

Salem · Accepted Answer · 2014-05-18 13:33:31Z

I think the easier way to achieve that would be using Gson.

If you are using gradle you can add it to your dependencies

compile 'com.google.code.gson:gson:2.2.4'

To use it you need to define classes to the objects you need to load. In your case it would be something like this:

// file MyObject.java
public class MyObject {
    List<Coord> results = new ArrayList<Coord>();    

    public static class Coord {
        public double lat;
        public double lon;
}

Then just use it to go to/from Json whenever you need:

String jsonDataString = this.getSharedPreferencesStringValue(ctx, "positions", "last_positions");
Gson gson = new Gson();
MyObject obj = gson.fromJson(jsonDataString, MyObject.class);
// Noew obj contains your JSON data, so you can manipulate it at your will.
Coord newCoord = new Coord();
newCoord.lat = 34.66;
newCoord.lon = -4.567;
obj.results.add(newCoord);
String newJsonString = gson.toJson(obj);

Rogue · Accepted Answer · 2014-05-17 23:56:32Z

3

SharedPreferences can only store basic type, such as String, integer, long, ... so you can't use it to store objects. However, you can store the Json String, using sharedPreferences.putString()

answered May 17, 2014 at 23:56

Rogue

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2 Comments

redrom Over a year ago

Yes, im converting created JSON into string before save using jsonData.toString(). Question is about creating JSON structure. not about purpose of saving JSON string in shared prefs.

Rogue Over a year ago

I don't get it, sorry, you want to edit your JSON object and edit the value in sharedPreferences ?

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