Android: String set preference is not persistent

问题

I have a problem with storing string set preference. I have these utility methods for storing:

public static void putStringSet(SharedPreferences pref, Editor e, String key, Set<String> set)
{
    if (Utils.isApiLevelGreaterThanGingerbread())
    {
        // e.remove(key); // I tried to remove it here
        e.putStringSet(key, set);
    }
    else
    {
        // removes old occurences of key
        for (String k : pref.getAll().keySet())
        {
            if (k.startsWith(key))
            {
                e.remove(k);
            }
        }

        int i = 0;
        for (String value : set)
        {
            e.putString(key + i++, value);
        }
    }
}

public static Set<String> getStringSet(SharedPreferences pref, String key, Set<String> defaultValue)
{
    if (Utils.isApiLevelGreaterThanGingerbread())
    {
        return pref.getStringSet(key, defaultValue);
    }
    else
    {
        Set<String> set = new HashSet<String>();

        int i = 0;

        Set<String> keySet = pref.getAll().keySet();
        while (keySet.contains(key + i))
        {
            set.add(pref.getString(key + i, ""));
            i++;
        }

        if (set.isEmpty())
        {
            return defaultValue;
        }
        else
        {
            return set;
        }
    }
}

I use these methods to be backward compatible with GB. But I have a problem that using putStringSet method isn't persistent for API > gingerbread. It is persistent while app is runing. But it dissapears after restart. I will describe the steps:

1. Clean install of application - there is no preference with key X
2. I store string set A with key X - preference contains A
3. I store string set B with key X - preference contains B
4. Close app
5. Restart of app - preference contains A
6. I store string set C with key X - preference contains C
7. Close app
8. Restart of app - preference contains A

So only the first value is persistent and I cannot overwrite it.

Other notes:

1. this methods just replaces putStringSet and getStringSet. So I use commit()...but elsewhere (see example below).
2. I tried to replace commit() with apply() - no success
3. When I use code for older APIs in newer APIs (I commented first 4 lines in both methods) it works flawlessly but it isn't so efficient

Example of use:

Editor e = mPref.edit();
PreferencesUtils.putStringSet(mPref, e, GlobalPreferences.INCLUDED_DIRECTORIES, dirs);
e.commit();

Thnak you very much for help.

回答1:

This has a ridiculous amount of duplicates - I bet that you do :

set = prefs.getStringSet("X", new HashSet<String>());
set.add("yada yada");
prefs.putStringSet("X", set);

In short android sees that set and the one inside refer to the same set and does nothing. Correct ?

See: Misbehavior when trying to store a string set using SharedPreferences

回答2:

My condition is very similar to yours, the only difference is when restart the app, preference contains A, B, C, but when reinstall it or reboot the phone, B&C are gone.

I also tried replace commit() with apply(), as this post adviced SharedPreferences not persistent , but still not to work.

I solved this problem by remove & commit the preference before replacing it:

editor.remove("StringSetKey");
editor.commit();

editor.putStringSet("StringSetKey", newSet);
editor.commit();

Ps: you can type adb pull /data/data/<packagename>/shared_prefs/xxxx.xml in cmd line to see if the commit() really works

Pps: I think this is a bug with putStringSet....

hope this will help you ;)

来源：https://stackoverflow.com/questions/16820252/android-string-set-preference-is-not-persistent