Equivalent of iOS NSNotificationCenter in Android?

Question

Is there an equivalent of the iOS class NSNotificationCenter in Android ? Are there any libraries or useful code available to me ?

Answer 1

In Android there is not a central notification center as in ios. But you can basically use Observable and Observer objects to achieve your task.

You can define a class like something below, just modify it for singleton use and add synchronized for concurrent use but the idea is the same:

public class ObservingService {
    HashMap<String, Observable> observables;

    public ObservingService() {
        observables = new HashMap<String, Observable>();
    }

    public void addObserver(String notification, Observer observer) {
        Observable observable = observables.get(notification);
        if (observable==null) {
            observable = new Observable();
            observables.put(notification, observable);
        }
        observable.addObserver(observer);
    }

    public void removeObserver(String notification, Observer observer) {
        Observable observable = observables.get(notification);
        if (observable!=null) {         
            observable.deleteObserver(observer);
        }
    }       

    public void postNotification(String notification, Object object) {
        Observable observable = observables.get(notification);
        if (observable!=null) {
            observable.setChanged();
            observable.notifyObservers(object);
        }
    }
}

Answer 2

Take a look at the Otto event bus from Square:

http://square.github.com/otto/

It has essentially the same features as NSNotificationCenter but thanks to annotations and static typing it is easier to follow the dependencies of components and paths that events follow. It's much simpler to use than the stock Android broadcast API, IMO.