SharedPreferences not to overwrite data

Question

I am trying to write a list with same values two times in the preferences and when I read it back I only get 1 result. Here is my SharedPreferences Code :

public void storeDeviceDetails(final ArrayList<String> deviceDetails) {
        SharedPreferences.Editor editor = context.getSharedPreferences("devicePrefs",Context.MODE_PRIVATE).edit();

        Set<String> set = new LinkedHashSet<>();
        set.addAll(deviceDetails);
        editor.putStringSet("deviceDetails", set);
        editor.apply();
    }

    public ArrayList<String> retrieveDeviceDetails() {
        SharedPreferences prefs = context.getSharedPreferences("devicePrefs", MODE_PRIVATE);
        ArrayList<String> details = null;

        Set<String> set = prefs.getStringSet("deviceDetails", null);

        if (set != null) {
            details = new ArrayList<>(set);
        }

        return details;
    }

I am writing it to List in 2 consecutive lines as -

MyPrefClass.storeDeviceDetails(myList);
MyPrefClass.storeDeviceDetails(myList);

And now in next line I do MyPrefClass.retrieveDeviceDetails(); I only get it as - [hero2lte, 7.0, hero2ltexx, SM-G935F, samsung]

Better provide a real [mcve] for us; instead of putting down parts of your code. — GhostCat, Mar 20 '17 at 13:53
you are passing a list to a set and a set does not hold duplicate values — giorashc, Mar 20 '17 at 13:55
Possible duplicate of [can i store two or more values with same key using SharedPreferences in android?](http://stackoverflow.com/questions/13623098/can-i-store-two-or-more-values-with-same-key-using-sharedpreferences-in-android) — denis_lor, Mar 20 '17 at 13:57

score 1 · Accepted Answer · answered Mar 20 '17 at 13:54

1

Set<String> set = new LinkedHashSet<>();

You're making a new set, so it's overwriting the old one completely.

Try getting the set that's already in SharedPreferences if it exists, and only make a new one if it doesn't. Something like this:

Set<String> set = prefs.getStringSet("deviceDetails", null);

if (set == null) {
    set = new LinkedHashSet<>();
}

Also, as mentioned in the comments, you're adding the same elements twice. Even if you were to fix it, a Set guarantees uniqueness, so they'd only be added once anyway.

answered Mar 20 '17 at 13:54

Cruncher

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Ok actually I am trying to save array list in shared prefs. How can i do this ? – MagdHo0506 Mar 20 '17 at 14:34
2

@Cruncher SharedPreferences doesn't store lists. If he needs that, he needs to use another storage mechanism. If set is sufficient for him, then your answer works. – Gabe Sechan Mar 20 '17 at 14:36
@GabeSechan Oh okay. Storing as a json array is probably the best thing then – Cruncher Mar 20 '17 at 14:37
Thank you all. I used this http://stackoverflow.com/questions/7057845/save-arraylist-to-sharedpreferences instead of set and it worked :) – MagdHo0506 Mar 20 '17 at 14:52

SharedPreferences not to overwrite data

1 Answers1