Make 'static' class observable

Question

I have a class Settings with static methods which I use to save and load my data. This is for example the Save() method:

public static void Save(SETTING_KEY key, String value)
{
    SharedPreferences sp = _context.getSharedPreferences(prefName, Context.MODE_PRIVATE);
    SharedPreferences.Editor editor = sp.edit();

    editor.putString(key.toString(), value);
    editor.commit();    
}

Now I'd like to make the class Settings observable. The problem is that extending my Settings-class from Observable does not work, as I don't instantiate this class as I only use its static methods.

Is there any easy way to make this static class observable?

the notions of staticity and heritance do not really work on the same plan, anyway. but it does not prevent you from having a list of observers and notifying them when you do something — njzk2, Jan 20 '14 at 23:23

score 2 · Accepted Answer · answered Jan 20 '14 at 23:32

Add your own observer mechanism. Simple implementation below

public interface Observer {
    void onSettingsChanged(String key, String value);
}

private static Observer observer;
public static void setObserver(Observer observer_) {
    observer = observer_;
}

public static void Save(SETTING_KEY key, String value) {
    SharedPreferences sp = _context.getSharedPreferences(prefName, Context.MODE_PRIVATE);
    SharedPreferences.Editor editor = sp.edit();

    editor.putString(key.toString(), value);
    editor.commit();
    if (observer != null) {
        observer.onSettingsChanged(key, value);
    }
}

You could also use a List<Observer> if you need more than 1 and you can also use some sort of event bus (e.g. Otto) system to publish events without having to provide a direct observer mechanism.

score 1 · Answer 2 · edited May 23 '17 at 12:26

1

You could try using a Singleton pattern? (Java Singleton Pattern)

That way, you can extend observable.

edited May 23 '17 at 12:26

Community

1
1

answered Jan 20 '14 at 23:23

Dannie

2,430
14
16

score 0 · Answer 3 · answered May 18 '17 at 21:01

You could combine a singleton with static methods.

class Settings extends Observable {
    private static Settings instance;
    private static synchronized Settings getInstance() {
        if(instance == null) {
            instance = new Settings();
        }
        return instance;
    }

    public static void Save(SETTING_KEY key, String value)
    {
        SharedPreferences sp = _context.getSharedPreferences(prefName, Context.MODE_PRIVATE);
        SharedPreferences.Editor editor = sp.edit();

        editor.putString(key.toString(), value);
        editor.commit();
        getInstance().notifyObservers(value); // or whatever
    }

    // can't override addObserver with a static method, so make a new method instead
    public static void addObserverStatic(Observer observer) {
        getInstance().addObserver(observer);
    }
}

As others have said, static methods on a singleton is a bit naughty. Do it some other way if you can.

Make 'static' class observable

3 Answers3