事件分发

   EventBus3.0的事件的分发时通过EventBus类中的post(粘性事件为postSticky)方法，post与postSticky的唯一区别就是，在postSticky内部首先会向EventBus类中的stickyEvents集合中添加事件类实例，然后在调用post方法；post方法的参数就是我们自己定义的事件类的实例；

post

public void post(Object event) {        PostingThreadState postingState = currentPostingThreadState.get();        List

    在事件分发之前，首先通过currentPostingThreadState内获取PostingThreadState;currentPostingThreadState是一个ThreadLocal<PostingThreadState>,我们知道ThreadLocal在java是保存每个线程中独立的数据,一般情况下，通过ThreadLocal.set() 到线程中的对象是该线程自己使用的对象，其他线程是不需要访问的，也访问不到的;而ThreadLocal存储的PostingThreadState类,就是个信息类;

final static class PostingThreadState {        final List

 

    获取到当前线程的PostingThreadState，并将需要处理的事件类实例添加到PostingThreadState的eventQuenue队列中;如果当前线程的Looper与主线程的Looper一致，这PostingThreadState的isMainThread为true;而PostingThreadState类中的isPosting来判断是否正在进行分发;最后通过postSingleEvent方法循环进行数据的分发处理;

  

private void postSingleEvent(Object event, PostingThreadState postingState) throws Error {        Class
      eventClass = event.getClass();        boolean subscriptionFound = false;        if (eventInheritance) {//是否触发订阅了该事件的基类以及接口类的相应方法            List
     
      > eventTypes = lookupAllEventTypes(eventClass);//查找event类所有的基类以及接口            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 (!subscriptionFound) {            if (logNoSubscriberMessages) {                Log.d(TAG, "No subscribers registered for event " + eventClass);            }            if (sendNoSubscriberEvent && eventClass != NoSubscriberEvent.class &&                    eventClass != SubscriberExceptionEvent.class) {                post(new NoSubscriberEvent(this, event));            }        }    }
     

     postSingleEvent方法首先通过lookupAllEventTypes方法查找出所有的event类中所有的基类以及接口;然后对这些循环进行分发;

private boolean postSingleEventForEventType(Object event, PostingThreadState postingState, Class
      eventClass) {        CopyOnWriteArrayList
     
       subscriptions;        synchronized (this) {            subscriptions = subscriptionsByEventType.get(eventClass);        }        if (subscriptions != null && !subscriptions.isEmpty()) {            for (Subscription subscription : subscriptions) {                postingState.event = event;                postingState.subscription = subscription;                boolean aborted = false;                try {                    postToSubscription(subscription, event, postingState.isMainThread);                    aborted = postingState.canceled;                } finally {                    postingState.event = null;                    postingState.subscription = null;                    postingState.canceled = false;                }                if (aborted) {                    break;                }            }            return true;        }        return false;    }
     

在postSingleEventForEventType方法中我们可以看到我们从EventBus类中subscriptionsByEventType中取出所有匹配的Subscription;并将Subscription实例中的event,subscription赋值给postingState;

private void postToSubscription(Subscription subscription, Object event, boolean isMainThread) {        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);        }    }

 在postToSubscription方法中，subscription.subscriberMethod.threadMode 4种线程模型,当线程模型为POSTING 时，直接执行invokeSubscriber方法，效率也最快;而invokeSubscriber方法也很简单，就是反射中的invoke方法;

   subscription.subscriberMethod.method.invoke(subscription.subscriber, event);