Save ArrayList to SharedPreferences

Question

I have an ArrayList with custom objects. Each custom object contains a variety of strings and numbers. I need the array to stick around even if the user leaves

Answer 1

You can save String and custom array list using Gson library.

=>First you need to create function to save array list to SharedPreferences.

public void saveListInLocal(ArrayList list, String key) {

        SharedPreferences prefs = getSharedPreferences("AppName", Context.MODE_PRIVATE);
        SharedPreferences.Editor editor = prefs.edit();
        Gson gson = new Gson();
        String json = gson.toJson(list);
        editor.putString(key, json);
        editor.apply();     // This line is IMPORTANT !!!

    }

=> You need to create function to get array list from SharedPreferences.

public ArrayList getListFromLocal(String key)
{
    SharedPreferences prefs = getSharedPreferences("AppName", Context.MODE_PRIVATE);
    Gson gson = new Gson();
    String json = prefs.getString(key, null);
    Type type = new TypeToken>() {}.getType();
    return gson.fromJson(json, type);

}

=> How to call save and retrieve array list function.

ArrayList listSave=new ArrayList<>();
listSave.add("test1"));
listSave.add("test2"));
saveListInLocal(listSave,"key");
Log.e("saveArrayList:","Save ArrayList success");
ArrayList listGet=new ArrayList<>();
listGet=getListFromLocal("key");
Log.e("getArrayList:","Get ArrayList size"+listGet.size());

=> Don't forgot to add gson library in you app level build.gradle.

implementation 'com.google.code.gson:gson:2.8.2'