关于android SharedPreference的问题

You should note that while keys are guaranteed to be unique in SharedPreferences, there's no guarantee that the values will be unique. As such, this function will only return the key for the first matching value.
 String findKey(SharedPreferences sharedPreferences, String value) {
    for (Map.Entry<String, ?> entry: sharedPreferences.getAll()) {
        if (value.equals(entry.getValue())) {
            return entry.getKey();
        }
    }
    return null; // not found
}