EventBus源码阅读（20）-EventBus注册

我们注册的时候是从调用register开始的，我们也从这里读起来！

register函数源码：

    /**     * Registers the given subscriber to receive events. Subscribers must call {@link #unregister(Object)} once they     * are no longer interested in receiving events.     * <p/>     * Subscribers have event handling methods that must be annotated by {@link Subscribe}.     * The {@link Subscribe} annotation also allows configuration like {@link     * ThreadMode} and priority.     */    public void register(Object subscriber) {        Class<?> subscriberClass = subscriber.getClass();//获取注册的上下文环境对应的类（activity/fragment）        List<SubscriberMethod> subscriberMethods = subscriberMethodFinder.findSubscriberMethods(subscriberClass);//获取该类对应的订阅方法列表        synchronized (this) {            for (SubscriberMethod subscriberMethod : subscriberMethods) {                subscribe(subscriber, subscriberMethod);//循环遍历注册（订阅者，订阅方法）            }        }    }

参数就是我们调用的常用的context

我们的Activity的类就是 subscriberClass

subscriberMethodFinder在上一节初始化的时候初始的。

下边就是对每一个订阅方法进行注册了。

subscribe方法：

    // Must be called in synchronized block    private void subscribe(Object subscriber, SubscriberMethod subscriberMethod) {        Class<?> eventType = subscriberMethod.eventType;        Subscription newSubscription = new Subscription(subscriber, subscriberMethod);        CopyOnWriteArrayList<Subscription> subscriptions = subscriptionsByEventType.get(eventType);//获取事件类型对应的订阅（订阅者，订阅者方法）        if (subscriptions == null) {//第一次注册该事件            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++) {//依据优先级，将新的订阅插入到表中            if (i == size || subscriberMethod.priority > subscriptions.get(i).subscriberMethod.priority) {                subscriptions.add(i, newSubscription);                break;            }        }<span style="white-space:pre"></span>//从上边可以看出，一个事件可以被多次订阅，可以在不同的Activity中订阅

</pre><pre name="code" class="java"><span style="white-space:pre"></span>//将订阅事件注册到依据订阅者进行存储的泪表中

        List<Class<?>> subscribedEvents = typesBySubscriber.get(subscriber);        if (subscribedEvents == null) {            subscribedEvents = new ArrayList<>();            typesBySubscriber.put(subscriber, subscribedEvents);        }        subscribedEvents.add(eventType);        if (subscriberMethod.sticky) {            if (eventInheritance) {//事件类型的继承关系                // 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<Class>).                Set<Map.Entry<Class<?>, Object>> entries = stickyEvents.entrySet();                for (Map.Entry<Class<?>, 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);            }        }    }

从代码中看，我们主要注册在三个地方

1、subscriptionsByEventType
注册的是（eventType，(subscriber, subscriberMethod)）

即：事件-> 注册（注册者（context），注册的方法（menthod））

把事件与对应的所有注册关联起来
2、typesBySubscriber

注册的是（subscriber, eventTypes）

即：注册者 ->  事件列表

就是把一个注册者与其注册的所有事件对应起来

3、stickyEvents

注册的是：事件类型 -> 事件

如果我们使用的是默认配置，则此处可以不看。

看看

checkPostStickyEventToSubscription

源码：

    private void checkPostStickyEventToSubscription(Subscription newSubscription, Object stickyEvent) {        if (stickyEvent != null) {            // If the subscriber is trying to abort the event, it will fail (event is not tracked in posting state)            // --> Strange corner case, which we don't take care of here.            postToSubscription(newSubscription, stickyEvent, Looper.getMainLooper() == Looper.myLooper());        }    }

    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);        }    }

上边这个函数就是依据 处理模式以及当前线程是否为主线程（UI线程），进行不同的处理。

发送事件

    void invokeSubscriber(Subscription subscription, Object event) {        try {            subscription.subscriberMethod.method.invoke(subscription.subscriber, event);        } catch (InvocationTargetException e) {            handleSubscriberException(subscription, event, e.getCause());        } catch (IllegalAccessException e) {            throw new IllegalStateException("Unexpected exception", e);        }    }

而对于sticky事件，如果初次注册，则不会出发之后的发送事件情况，当如果再次注册stcky事件（就是同一个sticky事件已经触发了，但当时没有人处理，此时注册处理该事件的activity，就会出发发送事件了）此时则会触发发送事件的情况。

此时我们已经看过的函数如下（红色点标记）