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

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 开发者_如何学编程save my markers/overlays offline for later use.

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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.

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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...

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You should use some persistent storage. SQLite would probably be the best option here. Overlays have their lat and lng. Just get them and whatever data you need along with them and put all these in the SQLite database. Then on Activity start get the points from database and show them on the map.

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Use a SQLite database to save the user data. They are simple and for a large amount of data they are better than SharedPreferences.

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