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EventBus 是一个 Android 事件发布/订阅框架，通过解耦发布者和订阅者简化 Android 事件传递，这里的事件可以理解为消息，本文中统一称为事件。事件传递既可用于 Android 四大组件间通讯，也可以用户异步线程和主线程间通讯等等。EventBus
EventBus3.0版本有较大的更新，性能上有很大提升。这里主要介绍新版本。
传统的事件传递方式包括：Handler、BroadCastReceiver、Interface 回调，相比之下 EventBus 的优点是代码简洁，使用简单，并将事件发布和订阅充分解耦。类似框架之前介绍过OTTO，地址http://blog.csdn.net/robertcpp/article/details/51502478。
共同点
1、都是事件总线框架，满足消息/事件传递的同时，也实现了组件间的解耦.
2、注册的共同点都是采用method方法进行一个集成。
3、都采用注解的方式来标注订阅方法(旧版本的EventBus通过固定方法名标记订阅者)
4、大部分规则相同，比如订阅方法只能有一个参数。
5、都不适用进程间通信
不同点
1、OTTO更加轻量级，结构简单。EventBus稍微复杂一些。
2、OTTO默认在主线程中使用，不能在其他线程使用，通过设置ThreadEnforcer可以在任意线程使用，但是消息传递不能指定目标线程，EventBus实现了4种ThreadMode，线程之间消息传递非常灵活。
3、EventBus支持粘性事件，而OTTO不支持。即先发消息，再注册订阅者仍然能够收到消息。
3、OTTO有默认的生产者方法，可以产生默认消息，EventBus没有
public class MessageEvent {
//定义相关属性
}eventBus.register(this);
@Subscribe
public void onEvent(MessageEvent event) {
//收到消息后的处理
};eventBus.post(event);
eventBus.unregister(this);
public static EventBus getDefault() {
if (defaultInstance == null) {
synchronized (EventBus.class) {
if (defaultInstance == null) {
defaultInstance = new EventBus();
}
}
}
return defaultInstance;
}Log.e(TAG, "SubscriberExceptionEvent subscriber " + subscription.subscriber.getClass()
+ " threw an exception", cause);
SubscriberExceptionEvent exEvent = (SubscriberExceptionEvent) event;
Log.e(TAG, "Initial event " + exEvent.causingEvent + " caused exception in "
+ exEvent.causingSubscriber, exEvent.throwable);
Log.e(TAG, "Could not dispatch event: " + event.getClass() + " to subscribing class "
+ subscription.subscriber.getClass(), cause);Log.d(TAG, "No subscribers registered for event " + eventClass);
SubscriberExceptionEvent exEvent = new SubscriberExceptionEvent(this, cause, event,subscription.subscriber); post(exEvent);
if (sendNoSubscriberEvent && eventClass != NoSubscriberEvent.class &&
eventClass != SubscriberExceptionEvent.class) {
post(new NoSubscriberEvent(this, event));
}if (logSubscriberExceptions) {
Log.e(TAG, "Could not dispatch event: " + event.getClass() + " to subscribing class "
+ subscription.subscriber.getClass(), cause);
}if (eventInheritance) {
List<Class<?>> eventTypes = lookupAllEventTypes(eventClass);
int countTypes = eventTypes.size();
for (int h = 0; h < countTypes; h++) {
Class<?> clazz = eventTypes.get(h);
subscriptionFound |= postSingleEventForEventType(event, postingState, clazz);
}
} else {
subscriptionFound = postSingleEventForEventType(event, postingState, eventClass);
}if (ignoreGeneratedIndex) {
subscriberMethods = findUsingReflection(subscriberClass);
} else {
subscriberMethods = findUsingInfo(subscriberClass);
}else if (strictMethodVerification && method.isAnnotationPresent(Subscribe.class)) {
String methodName = method.getDeclaringClass().getName() + "." + method.getName();
throw new EventBusException("@Subscribe method " + methodName +
"must have exactly 1 parameter but has " + parameterTypes.length);
}
} else if (strictMethodVerification && method.isAnnotationPresent(Subscribe.class)) {
String methodName = method.getDeclaringClass().getName() + "." + method.getName();
throw new EventBusException(methodName +
" is a illegal @Subscribe method: must be public, non-static, and non-abstract");
}public void register(Object subscriber) {
Class<?> subscriberClass = subscriber.getClass();
List<SubscriberMethod> subscriberMethods = subscriberMethodFinder.findSubscriberMethods(subscriberClass);
synchronized (this) {
for (SubscriberMethod subscriberMethod : subscriberMethods) {
subscribe(subscriber, subscriberMethod);
}
}
}private final Map<Class<?>, CopyOnWriteArrayList<Subscription>> subscriptionsByEventType; private final Map<Object, List<Class<?>>> typesBySubscriber;
throw new EventBusException("Subscriber " + subscriberClass
+ " and its super classes have no public methods with the @Subscribe annotation");throw new EventBusException("Subscriber " + subscriber.getClass() + " already registered to event "
+ eventType);private final Map<Class<?>, Object> stickyEvents;
public void post(Object event) {
PostingThreadState postingState = currentPostingThreadState.get();
List<Object> eventQueue = postingState.eventQueue;
eventQueue.add(event);
if (!postingState.isPosting) {
postingState.isMainThread = Looper.getMainLooper() == Looper.myLooper();
postingState.isPosting = true;
if (postingState.canceled) {
throw new EventBusException("Internal error. Abort state was not reset");
}
try {
while (!eventQueue.isEmpty()) {
postSingleEvent(eventQueue.remove(0), postingState);
}
} finally {
postingState.isPosting = false;
postingState.isMainThread = false;
}
}
}
public void postSticky(Object event) {
synchronized (stickyEvents) {
stickyEvents.put(event.getClass(), event);
}
// Should be posted after it is putted, in case the subscriber wants to remove immediately
post(event);
}
private final ThreadLocal<PostingThreadState> currentPostingThreadState = new ThreadLocal<PostingThreadState>() {
@Override
protected PostingThreadState initialValue() {
return new PostingThreadState();
}
};switch (subscription.subscriberMethod.threadMode) {
case POSTING:
invokeSubscriber(subscription, event);
break;
case MAIN:
if (isMainThread) {
invokeSubscriber(subscription, event);
} else {
mainThreadPoster.enqueue(subscription, event);
}
break;
case BACKGROUND:
if (isMainThread) {
backgroundPoster.enqueue(subscription, event);
} else {
invokeSubscriber(subscription, event);
}
break;
case ASYNC:
asyncPoster.enqueue(subscription, event);
break;
default:
throw new IllegalStateException("Unknown thread mode: " + subscription.subscriberMethod.threadMode);
}public synchronized void unregister(Object subscriber) {
List<Class<?>> subscribedTypes = typesBySubscriber.get(subscriber);
if (subscribedTypes != null) {
for (Class<?> eventType : subscribedTypes) {
unsubscribeByEventType(subscriber, eventType);
}
typesBySubscriber.remove(subscriber);
} else {
Log.w(TAG, "Subscriber to unregister was not registered before: " + subscriber.getClass());
}
}
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原文地址：http://blog.csdn.net/robertcpp/article/details/51546714
