Add EventService#subscribe(EventSubscriber) method

Otherwise, there is no way to register an EventSubscriber,
because the DefaultEventBus is not publicly accessible.

Author: ctrueden

pom.xml

@@ -10,7 +10,7 @@
 	</parent>
 
 	<artifactId>scijava-common</artifactId>
-	<version>2.93.2-SNAPSHOT</version>
+	<version>2.94.0-SNAPSHOT</version>
 
 	<name>SciJava Common</name>
 	<description>SciJava Common is a shared library for SciJava software. It provides a plugin framework, with an extensible mechanism for service discovery, backed by its own annotation processor, so that plugins can be loaded dynamically. It is used by downstream projects in the SciJava ecosystem, such as ImageJ and SCIFIO.</description>

src/main/java/org/scijava/event/DefaultEventService.java

@@ -138,6 +138,11 @@ public List<EventSubscriber<?>> subscribe(final Object o) {
 		return subscribers;
 	}
 
+	@Override
+	public void subscribe(final EventSubscriber<?> subscriber) {
+		eventBus.subscribe(subscriber.getClass(), subscriber);
+	}
+
 	@Override
 	public void unsubscribe(final Collection<EventSubscriber<?>> subscribers) {
 		for (final EventSubscriber<?> subscriber : subscribers) {

src/main/java/org/scijava/event/EventService.java

@@ -125,6 +125,24 @@ public interface EventService extends SciJavaService {
 	 */
 	List<EventSubscriber<?>> subscribe(Object o);
 
+	/**
+	 * Subscribes the given {@link EventSubscriber} to its associated event class.
+	 * Its {@link EventSubscriber#onEvent} method will be called whenever an event
+	 * of the matching type is published.
+	 * <p>
+	 * <strong>Important note:</strong> The event service does <em>not</em> keep a
+	 * strong reference to the subscriber! If you use this method, you are also
+	 * responsible for keeping a reference to the subscriber, or else it is likely
+	 * to be garbage collected, and thus no longer respond to events as intended.
+	 * One simple way to force a strong reference to exist is to add it to
+	 * SciJava's {@link org.scijava.object.ObjectService} via
+	 * {@link org.scijava.object.ObjectService#addObject}.
+	 * </p>
+	 * 
+	 * @param subscriber the event subscriber to register
+	 */
+	void subscribe(EventSubscriber<?> subscriber);
+
 	/**
 	 * Removes all the given subscribers; they will no longer be notified when
 	 * events are published.