How can I store an integer array in SharedPreferences?

Question

I want to save/recall an integer array using SharedPreferences. Is this possible?

Adrian Toman · Accepted Answer · 2012-06-19 03:43:55Z

57

You can try to do it this way:

Put your integers into a string, delimiting every int by a character, for example a comma, and then save them as a string:

SharedPreferences prefs = getPreferences(MODE_PRIVATE);
int[] list = new int[10];
StringBuilder str = new StringBuilder();
for (int i = 0; i < list.length; i++) {
    str.append(list[i]).append(",");
}
prefs.edit().putString("string", str.toString());

Get the string and parse it using StringTokenizer:

String savedString = prefs.getString("string", "");
StringTokenizer st = new StringTokenizer(savedString, ",");
int[] savedList = new int[10];
for (int i = 0; i < 10; i++) {
    savedList[i] = Integer.parseInt(st.nextToken());
}

edited Jun 19, 2012 at 3:43

Adrian Toman

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answered Aug 24, 2011 at 13:17

Egor

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2 Comments

Paweł Brewczynski Over a year ago

Note that this method could be used only when you have little amount of data, since String operations aren't efficient. (every character needs to be parsed when reading).

Julio_oa Over a year ago

According to the javadoc, the use of StringTokenizer is discouraged: docs.oracle.com/javase/7/docs/api/java/util/…, use String.split() instead. See here stackoverflow.com/questions/6983856/…

Rafael T · Accepted Answer · 2018-06-25 13:28:01Z

You can't put Arrays in SharedPreferences, but you can workaround:

private static final String LEN_PREFIX = "Count_";
private static final String VAL_PREFIX = "IntValue_";
public void storeIntArray(String name, int[] array){
    SharedPreferences.Editor edit= mContext.getSharedPreferences("NAME", Context.MODE_PRIVATE).edit();
    edit.putInt(LEN_PREFIX + name, array.length);
    int count = 0;
    for (int i: array){
        edit.putInt(VAL_PREFIX + name + count++, i);
    }
    edit.commit();
}
public int[] getFromPrefs(String name){
    int[] ret;
    SharedPreferences prefs = mContext.getSharedPreferences("NAME", Context.MODE_PRIVATE);
    int count = prefs.getInt(LEN_PREFIX + name, 0);
    ret = new int[count];
    for (int i = 0; i < count; i++){
        ret[i] = prefs.getInt(VAL_PREFIX+ name + i, i);
    }
    return ret;
}

Nick Bolton · Accepted Answer · 2012-06-26 05:28:44Z

5

Here's my version, based on Egor's answer. I prefer not to use StringBuilder unless I'm building an enourmous string, but thanks to Egor for using StringTokenizer -- haven't made much use of this in the past, but it's very handy! FYI, this went in my Utility class:

public static void saveIntListPrefs(
    String name, Activity activity, List<Integer> list)
{
  String s = "";
  for (Integer i : list) {
    s += i + ",";
  }

  Editor editor = activity.getPreferences(Context.MODE_PRIVATE).edit();
  editor.putString(name, s);
  editor.commit();
}

public static ArrayList<Integer> readIntArrayPrefs(String name, Activity activity)
{
  SharedPreferences prefs = activity.getPreferences(Context.MODE_PRIVATE);
  String s = prefs.getString(name, "");
  StringTokenizer st = new StringTokenizer(s, ",");
  ArrayList<Integer> result = new ArrayList<Integer>();
  while (st.hasMoreTokens()) {
    result.add(Integer.parseInt(st.nextToken()));
  }
  return result;
}

answered Jun 26, 2012 at 5:28

Nick Bolton

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1 Comment

Anthony Over a year ago

The for loop should be using StringBuilder class and not have string concatenation like this.

Risadinha · Accepted Answer · 2014-07-11 12:59:17Z

5

Two solutions:

(1) Use http://commons.apache.org/proper/commons-lang/apidocs/org/apache/commons/lang3/StringUtils.html

It has split/join functions that let you join and split the integers in one liners:

StringUtils.join([1, 2, 3], ';')  = "1;2;3"
StringUtils.split("1;2;3", ';')   = ["1", "2", "3"]

You'd still have to convert the strings back to integers, though.

Actually, for splitting java.lang.String.split() will work just as fine: http://docs.oracle.com/javase/7/docs/api/java/lang/String.html#split(java.lang.String)

(2) Use the SharedPreferences.putStringSet() (API 11):

    SharedPreferences.Editor editor = preferences.edit();
    int count = this.intSet.size();
    if (count > 0) {
        Set<String> theSet = new HashSet<String>();
        for (Long l : this.intSet) {
            theSet.add(String.valueOf(l));
        }
        editor.putStringSet(PREFS_KEY, theSet);
    } else {
        editor.remove(PREFS_KEY);
    }
    editor.commit();

And to get it back:

    Set<String> theSet = this.preferences.getStringSet(PREFS_KEY, null);
    if (theSet != null && !theSet.isEmpty()) {
        this.intSet.clear();
        for (String s : theSet) {
            this.intSet.add(Integer.valueOf(s));
        }
    }

This code does not catch the NPEs or NumberFormatExceptions because the intSet is otherwise assured to not contain any nulls. But of course, if you cannot assure that in your code you should surround this with a try/catch.

edited Jul 11, 2014 at 12:59

answered Jul 9, 2014 at 12:22

Risadinha

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4 Comments

Cobbles Over a year ago

Solution 2 is the way to go

blackwolf Over a year ago

The 2nd solution is nice, but it will lose the elements order.

Risadinha Over a year ago

@blackwolf Try it with java.util.SortedSet - maybe Android serializes it correctly.

blackwolf Over a year ago

'SharedPreferences' use 'HashSets'. See CommonsWare answer

GozzoMan · Accepted Answer · 2017-08-30 20:20:01Z

4

I like to use JSON, which can be stored and retrieved as a string, to represent any complex data in SharedPreferences. So, in the case of an int array:

public void setPrefIntArray(String tag, int[] value)
{
    SharedPreferences.Editor prefEditor = PreferenceManager.getDefaultSharedPreferences(context)
            .edit();

    String s;
    try
    {
        JSONArray jsonArr = new JSONArray();
        for (int i : value)
            jsonArr.put(i);

        JSONObject json = new JSONObject();
        json.put(tag, jsonArr);

        s = json.toString();
    }
    catch(JSONException excp)
    {
        s = "";
    }

    prefEditor.putString(tag, s);
    prefEditor.commit();
}

public int[] getPrefIntArray(String tag, int[] defaultValue)
{
    SharedPreferences pref = PreferenceManager.getDefaultSharedPreferences(context);

    String s = pref.getString(tag, "");

    try
    {
        JSONObject json = new JSONObject(new JSONTokener(s));
        JSONArray jsonArr = json.getJSONArray(tag);

        int[] result = new int[jsonArr.length()];

        for (int i = 0; i < jsonArr.length(); i++)
            result[i] = jsonArr.getInt(i);

        return result;
    }
    catch(JSONException excp)
    {
        return defaultValue;
    }
}

The beauty is that the same idea can be applied to any other complex data representable as a JSON.

answered Aug 30, 2017 at 20:20

GozzoMan

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1 Comment

Luís Henriques Over a year ago

This is by far the best and most versatile solution. You can make these methods static (just pass context or the SharedPreferences / Editor to the function) and put ir in a Utils class to use it anywhere.

Michael Geier · Accepted Answer · 2017-11-05 09:40:43Z

Here is how the "convert to comma-separated String" solution could look in Kotlin, implemented as extension functions:

fun SharedPreferences.Editor.putIntArray(key: String, value: IntArray): SharedPreferences.Editor {
    return putString(key, value.joinToString(
            separator = ",", 
            transform = { it.toString() }))
}

fun SharedPreferences.getIntArray(key: String): IntArray {
    with(getString(key, "")) {
        with(if(isNotEmpty()) split(',') else return intArrayOf()) {
            return IntArray(count(), { this[it].toInt() })
        }
    }
}

That way you can use putIntArray(String, IntArray) and getIntArray(String) just like the other put and set methods:

val prefs = getSharedPreferences(PREFS_NAME, Context.MODE_PRIVATE)
prefs.edit().putIntArray(INT_ARRAY_TEST_KEY, intArrayOf(1, 2, 3)).apply()
val intArray = prefs.getIntArray(INT_ARRAY_TEST_KEY)

Mieszko Koźma · Accepted Answer · 2022-06-09 15:11:23Z

0

I went for the below solution, it's the least verbose of what I could see in this thread (in my case I wanted to have a set as a collection). "value" is the of type Set<Int>.

Save:

sharedPreferences.edit {
    if (value.isNotEmpty()) {
        putStringSet(key, hashSetOf(*value.map { it.toString() }.toTypedArray()))
    } else {
        remove(key)
    }
}

Retrieve:

val stringSet = sharedPreferences.getStringSet(key, null)
if (stringSet.isNullOrEmpty()) return emptySet()

return setOf<Int>(*stringSet.map { Integer.valueOf(it) }.toTypedArray())

answered Jun 9, 2022 at 15:11

Mieszko Koźma

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Comments

Adrian Toman · Accepted Answer · 2012-06-19 05:06:10Z

-1

You can only save primitive values in sharedPreference. Use Sqlite instead.

edited Jun 19, 2012 at 5:06

Adrian Toman

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answered Aug 24, 2011 at 13:09

Vineet Shukla

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