Android面试框架源码-EventBus源码初探

1. EventBus.getDefault().register(this)

public void register(Object subscriber) {
    Class<?> subscriberClass = subscriber.getClass();
    List<SubscriberMethod> subscriberMethods = subscriberMethodFinder.findSubscriberMethods(subscriberClass);
    synchronized (this) {
        for (SubscriberMethod subscriberMethod : subscriberMethods) {
            subscribe(subscriber, subscriberMethod);
        }
    }
}

这个方法会得到 Activity或者Fragment的class， 然后以class 为key 把所有用@Subscribe标记的方法找到保存在一个Map集合中。

List findSubscriberMethods(Class subscriberClass) {
    List subscriberMethods = METHOD_CACHE.get(subscriberClass);
    //....省略

    if (ignoreGeneratedIndex) {
        subscriberMethods = findUsingReflection(subscriberClass);
    } else {
        subscriberMethods = findUsingInfo(subscriberClass);
    }
    if (subscriberMethods.isEmpty()) {
        //....省略
    } else {
        METHOD_CACHE.put(subscriberClass, subscriberMethods);
        return subscriberMethods;
    }
}

一个class 对应一个List 然后遍历List把每个SubscriberMethod 封装成对应的new Subscription(subscriber, subscriberMethod)同时得到eventType (就是@Subscribe注解方法的参数类型) class ，从另一个map中取出一个ArrayList 然后把新的Subscription放在这个list集合中，同时还回去判断他是否是sticky 。

// Must be called in synchronized block
private void subscribe(Object subscriber, SubscriberMethod subscriberMethod) {
    Class eventType = subscriberMethod.eventType;
    Subscription newSubscription = new Subscription(subscriber, subscriberMethod);
    CopyOnWriteArrayList subscriptions = subscriptionsByEventType.get(eventType);
    if (subscriptions == null) {
        subscriptions = new CopyOnWriteArrayList<>();
        subscriptionsByEventType.put(eventType, subscriptions);
    } else {
        if (subscriptions.contains(newSubscription)) {
            throw new EventBusException("Subscriber " + subscriber.getClass() + " already registered to event "
                    + eventType);
        }
    }

    int size = subscriptions.size();
    for (int i = 0; i <= size; i++) {
        if (i == size || subscriberMethod.priority > subscriptions.get(i).subscriberMethod.priority) {
            subscriptions.add(i, newSubscription);
            break;
        }
    }

    List> subscribedEvents = typesBySubscriber.get(subscriber);
    if (subscribedEvents == null) {
        subscribedEvents = new ArrayList<>();
        typesBySubscriber.put(subscriber, subscribedEvents);
    }
    subscribedEvents.add(eventType);

    if (subscriberMethod.sticky) {
        if (eventInheritance) {
            // Existing sticky events of all subclasses of eventType have to be considered.
            // Note: Iterating over all events may be inefficient with lots of sticky events,
            // thus data structure should be changed to allow a more efficient lookup
            // (e.g. an additional map storing sub classes of super classes: Class -> List).
            Set, Object>> entries = stickyEvents.entrySet();
            for (Map.Entry, Object> entry : entries) {
                Class candidateEventType = entry.getKey();
                if (eventType.isAssignableFrom(candidateEventType)) {
                    Object stickyEvent = entry.getValue();
                    checkPostStickyEventToSubscription(newSubscription, stickyEvent);
                }
            }
        } else {
            Object stickyEvent = stickyEvents.get(eventType);
            checkPostStickyEventToSubscription(newSubscription, stickyEvent);
        }
    }
}

至此所有的订阅者都保存在subscriptionsByEventType map集合中，key是被订阅方法参数类型的class，value是一个订阅方法集合Subscription，Subscription内包含有Activity 或者Fragment的class 以及 对应的SubscriberMethod.

2. EventBus.getDefault().post(message)
   它会首先从ThreadLocal 中拿到当前线程 判断是主线城还是子线程，然后获取到当前线程的线程队列，把消息内容添加进去。最后循环执行postSingleEvent

public void post(Object event) {
   //从ThreadLocal 中拿到当前线程信息
    PostingThreadState postingState = currentPostingThreadState.get();
    //并把消息添加到这个线程的消息队列中
    List