import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;

public class EventBus {
	private static volatile EventBus defaultInstance;
	private final HashMap<Class<?>, ArrayList<SubscriberMethod>> events;

	private EventBus() {
		events = new HashMap<Class<?>, ArrayList<SubscriberMethod>>();
	}

	public static EventBus instance() {
		if (defaultInstance == null) {
			synchronized (EventBus.class) {
				if (defaultInstance == null) {
					defaultInstance = new EventBus();
				}
			}
		}
		return defaultInstance;
	}

	public void register(Object subscriber, Class<?> eventType) throws NoSuchMethodException {
		register(subscriber, "onEvent", eventType);
	}

	public synchronized void register(Object subscriber, String method, Class<?> eventType)
			throws NoSuchMethodException {
		SubscriberMethod subscriberMethod = getSubscriberMethod(subscriber, method, eventType);
		if (events.containsKey(eventType)) {
			events.get(eventType).add(subscriberMethod);
		} else {
			ArrayList<SubscriberMethod> methods = new ArrayList<SubscriberMethod>();
			methods.add(subscriberMethod);
			events.put(eventType, methods);
		}
	}

	public void unregister(Object subscriber, Class<?> eventType) throws NoSuchMethodException {
		unregister(subscriber, "onEvent", eventType);
	}

	public synchronized void unregister(Object subscriber, String method, Class<?> eventType)
			throws NoSuchMethodException {
		if (events.containsKey(eventType)) {
			SubscriberMethod sm = getSubscriberMethod(subscriber, method, eventType);
			ArrayList<SubscriberMethod> list = events.get(eventType);
			Iterator<SubscriberMethod> iterator = list.iterator();
			while (iterator.hasNext()) {
				SubscriberMethod subscriberMethod = iterator.next();
				if (subscriberMethod.equals(sm)) {
					iterator.remove();
				}
			}
		}
	}

	private SubscriberMethod getSubscriberMethod(Object subscriber, String method,
			Class<?> eventType) throws NoSuchMethodException {
		Method m = subscriber.getClass().getDeclaredMethod(method, eventType);
		if (!m.isAccessible()) {
			m.setAccessible(true);
		}
		return new SubscriberMethod(subscriber, m, eventType);
	}

	public void post(Object event) {
		try {
			ArrayList<SubscriberMethod> list = events.get(event.getClass());
			if (list != null) {
				Iterator<SubscriberMethod> iterator = list.iterator();
				while (iterator.hasNext()) {
					SubscriberMethod sm = iterator.next();
					sm.method.invoke(sm.subscriber, event);
				}
			}
		} catch (Exception e) {
			Log.e("EventBus post error", e);
		}
	}

}
 

import java.lang.reflect.Method;

final class SubscriberMethod {
	final Object subscriber;
	final Method method;
	final Class<?> eventType;
	/** Used for efficient comparison */
	String methodString;

	SubscriberMethod(Object subscriber, Method method, Class<?> eventType) {
		this.subscriber = subscriber;
		this.method = method;
		this.eventType = eventType;
	}

	@Override
	public boolean equals(Object other) {
		if (other instanceof SubscriberMethod) {
			checkMethodString();
			SubscriberMethod otherSubscriberMethod = (SubscriberMethod) other;
			otherSubscriberMethod.checkMethodString();
			// Don't use method.equals because of
			// http://code.google.com/p/android/issues/detail?id=7811#c6
			return methodString.equals(otherSubscriberMethod.methodString);
		} else {
			return false;
		}
	}

	private synchronized void checkMethodString() {
		if (methodString == null) {
			// Method.toString has more overhead, just take relevant parts of
			// the method
			StringBuilder builder = new StringBuilder(128);
			builder.append(subscriber.getClass().getName());
			builder.append('#').append(method.getName());
			builder.append('(').append(eventType.getName());
			methodString = builder.toString();
		}
	}

}