Android array to Sharedpreferences with Gson

Question

I need to create an array of the last 5 call dates.

I know that I have to save the date on the array but I don't know how to reorder the other records to keep this last call date the 1st record. And always maintain only 5 records

The Goal is to save that last call string and add to the array, after that I reorder to and maintain only the 5 records, after that I use FlexJson to make a string and save on sharedpreferences. Anyone have this full process?

Here what I'm doing but is throwing errors everywhere:

SAVE

SimpleDateFormat df = new SimpleDateFormat("HH:mm:ss dd-MM-yyyy", Locale.getDefault());
Calendar calendar = Calendar.getInstance();
String currentDateTimeString = df.format(calendar.getTime());

List<String> textList = new ArrayList<>();
JSONSerializer ser = new JSONSerializer();
textList.add(currentDateTimeString);

String jsonText = ser.deepSerialize(textList);

editor.putString("lastCall", jsonText);
editor.commit();

READ:

String lastCall = callLogPreferences.getString("lastCall", null);
JSONDeserializer<List<String>> der = new JSONDeserializer<>();
List<String> textList = der.deserialize(lastCall);

I'm using FlexJson: GSON and InstanceCreator issue

It's not converting from string to Array List

Answer 1

Try using an ArrayList with a custom Comparator as seen here: Sort ArrayList of custom Objects by property

Then, sort the ArrayList accordingly.

Answer 2

First let me give you an advise - if you have 3 question create 3 topics, not one with all the questions. Based on the question title: Android array to sharedpreferences I'll give an answer just to this issue.

So from your question you want to store a List<String> myList inside SharedPreferences. To do so I advise you to use Gson because it's simple. The main idea it's to serialize your List to a String in json and then store that String:

Since you are using primitive types you don't need to specify a TypeToken so you just need to:

public static final MY_LIST = "my_list";

List<String> myList = new ArrayList<String>();
SharedPreferences.Editor editor = prefs.edit();
editor.putString(MY_LIST, new Gson().toJson(myList));
editor.commit();

And it's stored. To retrieve the list just do the opposite:

myList = new Gson().fromJson(prefs.getString(MY_LIST, null), List<String>);

And that's it!
Hope it helped.

ps: SharedPreferences it's used to store values that can be accessed in other Classes/Activities/etc.. or to persist information between app restarts. You don't need this to accomplish what you want: Create a list with 5 ordered strings.

EDIT: this lib may save you some time with the serialization ;)