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

Hi @GuilhE if you check the link on my question you will see that FlexJson don't require a InstanceCreator, I used GSON but it was throwing that error. — FilipeOS
– FilipeOS, Commented Jun 4, 2015 at 21:42
I find Gson more straightforward. Can you post you Gson serialize code and error? — GuilhE
– GuilhE, Commented Jun 4, 2015 at 21:46
Hi @GuilhE I don't have it, I've seen in some stackoverflow topic. Can you show me an answer how to make a array list into string and then the string to array list with GSON? Thank you — FilipeOS
– FilipeOS, Commented Jun 4, 2015 at 22:04

GuilhE · Accepted Answer · 2017-11-05 18:37:14Z

5

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 ;)

edited Nov 5, 2017 at 18:37

answered Jun 4, 2015 at 22:17

GuilhE

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3 Comments

FilipeOS Over a year ago

Hi, so I need to .add the strings to that myList right? ( myList.add("x"); )

GuilhE Over a year ago

Yes, the code I gave you here it's just an example on how to store a List inside SharedPreferences. If the List has elements, ordered or not, or it's empty it's up to you.

FilipeOS Over a year ago

dateList = new Gson().fromJson(callLogPreferences.getString("lastCall", null), new TypeToken<List<String>>(){ ---> make the job on your last code tip! THANK YOU

Community · Accepted Answer · 2017-05-23 11:44:53Z

1

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

Then, sort the ArrayList accordingly.

edited May 23, 2017 at 11:44

CommunityBot

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answered Jun 4, 2015 at 20:31

Tukajo

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4 Comments

Tukajo Over a year ago

No sorry, the above link is more than sufficient for what I believe you are asking. I am not here to do your job :). However if you feel my answer has not been sufficient, please extend details or clarify for me and I will do my best to reply with additional information/correct what I have said.

FilipeOS Over a year ago

Hi there, okay no problem, I'm a noob and your answer is like nothing to me :( sorry. If you cannot make a better example I understand

Tukajo Over a year ago

From what I understand you are writing the JSON above to sharedPreferences, then attempting to retrieve the JSON data back. Correct?

FilipeOS Over a year ago

Yes, some guy told me that I need to convert the array to string with json, save with sharedpreferences and then convert the json string into array again to read the data and place on that expandable listview. But it's not working :( I've the 3 topics about what is not working

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