Set<String> in android sharedpreferences does not save on force close

You can also work around the bug mentioned by g00dy this way:

Get the set from sharedPreferences and save it in a variable.

Then just delete the set in sharedpreferences before adding it again when saving.

SharedPreferences.Editor editor= sharedPref.edit();
editor.remove("mSet");
editor.apply(); 
editor.putStringSet("mSet", mSet);
editor.apply();

Make sure to use apply() or commit() twice.

Alternatively, if you are working in Kotlin simply :

PreferenceManager.getDefaultSharedPreferences(applicationContext)
    .edit {
        this.remove("mSet")
        this.apply()
        this.putStringSet("mSet", mSet)
    }

Take a look here.

Also for refference:

SharedPreferences

SharedPreferences.Editor

EDIT:

There's actually a bug with this one, see here. An extract from there:

This problem is still present on the 17 API level.

It is caused because the getStringSet() method of the SharedPreferences class doesn't return a copy of the Set object: it returns the entire object and, when you add new elements to it, the commitToMemory method of the SharedPrefencesImpl.EditorImpl class see that the existing value is equal to the previous one stored.

The ways to workaround this issue is to make a copy of the Set returned by SharedPreferences.getStringSet or force the write to memory using other preference that always change (for example, a property that stores the size of the set each time)

EDIT2:

There might be a solution here, take a look.