Set<String> losing data when restored from SharedPreferences after app is restarted

Question

Im using SharedPreference on android to store a Set of Strings. It is stored and retrived fine to my knowledge but when the app is restarted some data is lost. Strings are add one by one and before adding them I retrieve the set, add a String and then store it again.

This is how I store it:

Set<String> emptySet = null;
            SharedPreferences prefs = getContext().getSharedPreferences(getContext().getString(R.string.pref_disagree_key), Activity.MODE_PRIVATE);

            String newIdAgreed = getItem(position).getId();

            if (prefs.contains(getContext().getString(R.string.pref_disagree_key))) {

                Set<String> updateSet = prefs.getStringSet(getContext().getString(R.string.pref_disagree_key), emptySet);
                updateSet.add(newIdAgreed);
                SharedPreferences.Editor editor = prefs.edit();
                editor.putStringSet(getContext().getString(R.string.pref_disagree_key), updateSet);
                editor.commit();

            } else {
                Set<String> newSet = new HashSet<String>();
                newSet.add(newIdAgreed);
                SharedPreferences.Editor editor = prefs.edit();
                editor.putStringSet(getContext().getString(R.string.pref_disagree_key), newSet);
                editor.commit();
            }

And this is how I get it back:

if (prefsDisagree.contains(getContext().getString(R.string.pref_disagree_key))){
        disagree_set = new HashSet<String>(prefsDisagree.getStringSet(getContext().getString(R.string.pref_disagree_key), emptySet));
        for (String item: disagree_set){
            //stuff done here


        }
}

I saw some similar questions about this topic but none of the answers solved my problem. Any ideas?

Answer 1

The StringSet is not persistent when you are trying to edit it all again after it was saved and therefore newer data that was just added wont get saved when you quit the app and open it again.

It is actually documented: getStringSet

You need to copy first the StringSet and then insert/add data to the copied StringSet:

Set<String> s = new HashSet<String(prefs.getStringSet(
               getContext().getString(R.string.pref_disagree_key), 
               emptySet));