How to save an array of strings with SharedPreferences?

Question

I have an array of Strings, I need to save this array with SharedPreferences, and then read and display them on a ListView.

For now, I use this algorithm:

SharedPreferences sp = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());

//To save the strings
public void saveStrings(String[] str){
    int a = 0;
    int lenght = str.length;
    while (a<lenght){
        sp.edit().putString(Integer.toString(a), Integer.toString(str[a])).apply();
        a=a+1;
    }
}

//To read the strings
public String[] getStrings(){
    String[] str = new String [8];
    int a = 0;
    int lenght = 8; //To read 8 strings
    while (a<lenght){
        str[a] = sp.getString(Integer.toString(a),"Null");
        a=a+1;
    }
return str;
}

Is there a way to save and read the entire array, rather than a string at a time?

For this project I'm using API level 19 (Android 4.4.2 KitKat)

Look at this question: stackoverflow.com/questions/4064901/… — SaDeGH_F
– SaDeGH_F, Commented May 18, 2014 at 18:43
Use GSON. Here is your solution: - stackoverflow.com/a/20848025/1787135 — jpardogo
– jpardogo, Commented May 18, 2014 at 20:44

matiash · Accepted Answer · 2014-05-18 18:54:30Z

2

Well, you could use putStringSet(), but (a) it's only from API level 11 onwards, and (b) as its name says, it's for sets (which means that you will lose the original ordering and any duplicates present in the array).

We solved this problem by "encoding" collections into a string and using putString() and decoding them afterwards on getString(), with this pair of methods (for ArrayList, but should be easily convertible into array versions):

public String encodeStringList(List<String> list, char separator)
{
    StringBuilder sb = new StringBuilder(list.size() * 50);

    for (String item : list)
    {
        if (sb.length() != 0)
            sb.append(separator);

        // Escape the separator character.
        sb.append(item.replace(Character.toString(separator), "\\" + separator));
    }

    return sb.toString();
}

public List<String> decodeStringList(String encoded, char separator)
{
    ArrayList<String> items = new ArrayList<String>();

    if (encoded != null && encoded.length() != 0)
    {
        // Use negative look-behind with backslash, because it's used for escaping the separator.
        // Expression is "(?<!\)s" with doubling because of escaping in regex, and again because of escaping in Java).
        String splitter = "(?<!\\\\)" + separator; //$NON-NLS-1$
        String[] parts = encoded.split(splitter);

        // While converting to list, take out the escape characters used to escape the now-removed separator.
        for (int i = 0; i < parts.length; i++)
            items.add(parts[i].replace("\\" + separator, Character.toString(separator)));
    }

    return items;
}

answered May 18, 2014 at 18:54

matiash

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2 Comments

user3605220 Over a year ago

Thanks for your answer, but I understand that I can't use this method, because I have a lot of duplicates, and I can't lose the duplicates!

matiash Over a year ago

@Salvuccio96 In case I wasn't clear, this method does preserve duplicates, just call putString(). I was warning against putStringSet().

Community · Accepted Answer · 2017-05-23 11:50:23Z

0

Set<String> set =list.getStringSet("key", null); Set<String> set = new HashSet<String>(); set.addAll(list of the string list u have); editor.putStringSet("key", set); editor.commit();
Please refer to this thread for further details Save ArrayList to SharedPreferences

edited May 23, 2017 at 11:50

CommunityBot

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answered May 18, 2014 at 18:42

Kosh

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Comments

Ronn Wilder · Accepted Answer · 2014-05-18 20:13:40Z

0

//while storing
str is string array
String fin="";
for(i=0;i<n;i++){
    fin=fin+str[i]+",";
}
fin=fin.substring(0,fin.length()-1);

//while retrieving
List<String> items = Arrays.asList(fin.split("\\s*,\\s*"));

answered May 18, 2014 at 20:13

Ronn Wilder

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1 Comment

Ronn Wilder Over a year ago

the split function here will see for spaces zero or more then a literal comma and then again spaces zero or more.

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