How to save added google maps overlays in an android app?

Question

I created an app in which users can add various markers on google maps using overlays. I want the app to save the overlay when the user creates it so that when they re-open the app later the markers will still be present.
Currently anytime the app is re-opened the created markers are gone. I have searched the internet and have not gotten a clear understanding of how to save my markers/overlays offline for later use.

Answer 1

As mentioned, you need to use some persistent storage. Perhaps, database would be an excess in your particular case (if you simply need to save a bunch of longitude-latitude pairs), and Shared Preferences would fit your needs. If you rarely need to read/store this data, then putting JSONArray as a String to Shared Preferences would be the simplest (in terms of reading and extracting data) solution:

    SharedPreferences.Editor editor = getSharedPreferences("name", 0).edit();
    JSONArray jsonArr = new JSONArray();
    JSONObject json;
    for (int i = 0; i < user_markers.size(); i++) { // here I assume that user_markers is a list where you store markers added by user
        json = new JSONObject();
        json.put("lat", user_markers.get(i).getLat());
        json.put("long", user_markers.get(i).getLong());
        jsonArr.put(json);
    }
    editor.putString("markers", jsonArr.toString());
    editor.commit();

If you need to read/store this data a bit more often, then you may assign ids/indexes to separate SharedPreferences's values, but this may require more complicated extraction method. For example:

    SharedPreferences.Editor editor = getSharedPreferences("name", 0).edit();
    int id;
    for (int i = 0; i < user_markers.size(); i++) { // here I assume that user_markers is a list where you store markers added by user
        id = user_markers.get(i).getId(); // some Id here
        // or simply id = i;
        editor.putString("markers_lat_" + id, user_markers.get(i).getLat());
        editor.putString("markers_long_" + id, user_markers.get(i).getLong());
    }
    editor.commit();

After all, you should consider using database if you plan to store big amount of data or data of complicated structure.

Answer 2

It just an idea, but you can save your markers in database and when you reopen your map just query database and put it on the map again...