EventDispatcher.java

package ninja.ugly.prevail.event.dispatcher;

/**
 * An EventDispatcher is responsible for delivering events generated by EventFactories during operations
 * on Chunks.
 * <p>
 * This interface is intended to be implemented by instances that use, for example, Guava's EventBus or GreenRobot's
 * EventBus on Android.  Such implementations use runtime types to match events to subscribers. As such,
 * the methods in this class are type-free.
 */
public interface EventDispatcher {

  /**
   * Dispatch an arbitrary event object to the registered subscribers.
   *
   * @param event The event to dispatch.
   */
  void dispatchEvent(Object event);

  /**
   * Register a subscriber with this EventDispatcher.
   *
   * @param subscriber The subscriber to register.
   */
  void register(Object subscriber);

  /**
   * Unregister a subscriber from this EventDispatcher.
   *
   * @param subscriber The subscriber to unregister.
   */
  void unregister(Object subscriber);

  /**
   * An empty implementation of the EventDispatcher.  Useful to instantiate as an initial value inside
   * a Chunk, rather than null.
   */
  public static final class EmptyEventDispatcher implements EventDispatcher {
    @Override
    public void dispatchEvent(final Object event) {
      // Do nothing.
    }

    @Override
    public void register(final Object subscriber) {
      // Do nothing.
    }

    @Override
    public void unregister(final Object subscriber) {
      // Do nothing
    }
  }
}