Android – unable to listen to preference changes?

class Userviewmodel extends viewmodel{
    appPrefs.registerOnSharedPreferencechangelistener(preferencechangelistener)
}}

private SharedPreferences.OnSharedPreferencechangelistener preferencechangelistener;

public void subscribe() {

 preferencechangelistener = (sharedPreferences, key) -> {

        }
    };
    appPrefs.registerOnSharedPreferencechangelistener(preferencechangelistener);

};

public void unsubscribe(){
    appPrefs.unregisterOnSharedPreferencechangelistener(preferencechangelistener);
}

Subscribe() and unsubscribe() are called from fragment onattach() and ondetach() methods, but they do not work when the property state changes. As you can see, preferencechangelistener is a class member rather than a method property. The value of preference is changed in another fragment. When I navigate to another fragment and return that preferencechangelistener is null, it is in onattach() I see the reason, but I don't know how to overcome it

resolvent:

I suggest registering onsharedpreferencechangelistener() during fragment onresume() and unregisteronsharedpreferencechangelistener() at onpause(). Also check the content of the preference name. This may be a typo

`

 public void onSharedPreferenceChanged(SharedPreferences sharedPreferences,
            String key) {
            if (key.equals(KEY_PREF_SYNC_CONN)) {
                Preference connectionPref = findPreference(key);
                // Set summary to be the user-description for the selected value
                connectionPref.setSummary(sharedPreferences.getString(key, ""));
            }
        }

`Official documents can be found here: https://developer.android.com/guide/topics/ui/settings.html#Fragment