EventBus-源码解析

基于eventbus 2.4.0
项目中很多地方用到EventBus
大体的使用 就是这样的几段代码

// 注册
EventBus.getDefault().register(this);
// 发送
 EventBus.getDefault().post(new Event());
// 响应
public void onEventMainThread(Event event) {
}
// 取消注册
EventBus.getDefault().unregister(this);

EventBus.getDefault() 利用单例模式获取的是EventBus实例。
register 方法

// 采用的是订阅者模式
private synchronized void register(Object subscriber, boolean sticky, int priority) {
        // findSubscriberMethods 通过反射获取subscriber的 onEventMainThread方法
        List subscriberMethods = this.subscriberMethodFinder.findSubscriberMethods(subscriber.getClass());
        // 获取迭代器
        Iterator i$ = subscriberMethods.iterator();
        // 遍历订阅
        while(i$.hasNext()) {
            SubscriberMethod subscriberMethod = (SubscriberMethod)i$.next();
            // 订阅
            this.subscribe(subscriber, subscriberMethod, sticky, priority);
        }

    }

SubscriberMethod 类中保存了 响应Method

订阅方法里是怎么做的？大体思路是按照优先级把一个个Subscription对象（包含注册对象）放入EventType对应的List中，再把注册对象的EventType放到对应的List中。

private void subscribe(Object subscriber, SubscriberMethod subscriberMethod, boolean sticky, int priority) {
        Class eventType = subscriberMethod.eventType;
        CopyOnWriteArrayList subscriptions = (CopyOnWriteArrayList)this.subscriptionsByEventType.get(eventType);
         // 利用订阅者对象和响应方法创建一个新的对象
        Subscription newSubscription = new Subscription(subscriber, subscriberMethod, priority);
        if (subscriptions == null) {
            subscriptions = new CopyOnWriteArrayList();
            this.subscriptionsByEventType.put(eventType, subscriptions);
        } else if (subscriptions.contains(newSubscription)) {
            // 一个对象只允许注册一次
            throw new EventBusException("Subscriber " + subscriber.getClass() + " already registered to event " + eventType);
        }

        int size = subscriptions.size();
        // 添加到此事件对应的list里
        for(int i = 0; i <= size; ++i) {
            if (i == size || newSubscription.priority > ((Subscription)subscriptions.get(i)).priority) {
                subscriptions.add(i, newSubscription);
                break;
            }
        }
         // 通过注册的对象 获取注册的event类对象
        List> subscribedEvents = (List)this.typesBySubscriber.get(subscriber);
        if (subscribedEvents == null) {
            subscribedEvents = new ArrayList();
            this.typesBySubscriber.put(subscriber, subscribedEvents);
        }

        ((List)subscribedEvents).add(eventType);
        if (sticky) {
            // sticky 默认false 暂时不研究 
            Map var11 = this.stickyEvents;
            Object stickyEvent;
            synchronized(this.stickyEvents) {
                stickyEvent = this.stickyEvents.get(eventType);
            }

            if (stickyEvent != null) {
                this.postToSubscription(newSubscription, stickyEvent, Looper.getMainLooper() == Looper.myLooper());
            }
        }

    }

取消注册大体就是反过来清空。
复杂的是发送事件的过程，涉及到线程切换。

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