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

/**
 *     Save and get ArrayList in SharedPreference
 */

JAVA:

public void saveArrayList(ArrayList list, String key){
    SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(activity);
    SharedPreferences.Editor editor = prefs.edit();
    Gson gson = new Gson();
    String json = gson.toJson(list);
    editor.putString(key, json);
    editor.apply();    

}

public ArrayList getArrayList(String key){
    SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(activity);
    Gson gson = new Gson();
    String json = prefs.getString(key, null);
    Type type = new TypeToken>() {}.getType();
    return gson.fromJson(json, type);
}

Kotlin

fun saveArrayList(list: java.util.ArrayList?, key: String?) {
    val prefs: SharedPreferences = PreferenceManager.getDefaultSharedPreferences(activity)
    val editor: Editor = prefs.edit()
    val gson = Gson()
    val json: String = gson.toJson(list)
    editor.putString(key, json)
    editor.apply()
}

fun getArrayList(key: String?): java.util.ArrayList? {
    val prefs: SharedPreferences = PreferenceManager.getDefaultSharedPreferences(activity)
    val gson = Gson()
    val json: String = prefs.getString(key, null)
    val type: Type = object : TypeToken?>() {}.getType()
    return gson.fromJson(json, type)
}