【Android】事件总线（解耦组件） EventBus 详解

//定义事件类型：
publicclassMyEvent{}
//定义事件处理方法：
publicvoid onEventMainThread
//注册订阅者：
EventBus.getDefault().register(this)
//发送事件：
EventBus.getDefault().post(newMyEvent())
//实现

// EventType -> List<Subscription>，事件到订阅对象之间的映射
privatefinalMap<Class<?>,CopyOnWriteArrayList<Subscription>> subscriptionsByEventType;
// Subscriber -> List<EventType>，订阅源到它订阅的的所有事件类型的映射
privatefinalMap<Object,List<Class<?>>> typesBySubscriber;
// stickEvent事件，后面会看到
privatefinalMap<Class<?>,Object> stickyEvents;
// EventType -> List<? extends EventType>，事件到它的父事件列表的映射。即缓存一个类的所有父类
privatestaticfinalMap<Class<?>,List<Class<?>>> eventTypesCache =newHashMap<Class<?>,List<Class<?>>>();

public void register(Object subscriber) {
    register(subscriber, defaultMethodName, false, 0);
}

public void register(Object subscriber, int priority) {
    register(subscriber, defaultMethodName, false, priority);
}

public void registerSticky(Object subscriber) {
    register(subscriber, defaultMethodName, true, 0);
}

public void registerSticky(Object subscriber, int priority) {
    register(subscriber, defaultMethodName, true, priority);
}

private synchronized void register(Object subscriber, String methodName, boolean sticky, int priority) {
    List<SubscriberMethod> subscriberMethods = subscriberMethodFinder.findSubscriberMethods(subscriber.getClass(),
methodName);
    for (SubscriberMethod subscriberMethod : subscriberMethods) {
        subscribe(subscriber, subscriberMethod, sticky, priority);
    }
}

public void post(Object event) {
    PostingThreadState postingState = currentPostingThreadState.get();
    List<Object> eventQueue = postingState.eventQueue;
    eventQueue.add(event);
    if (postingState.isPosting) {
        return;
    } else {
        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;
            }
    }
}

final static class PostingThreadState {
    List<Object> eventQueue = new ArrayList<Object>();
    boolean isPosting;
    boolean isMainThread;
    Subscription subscription;
    Object event;
    boolean canceled;
}

private final PendingPostQueue queue;

public void enqueue(Subscription subscription, Object event) {
    PendingPost pendingPost = PendingPost.obtainPendingPost(subscription, event);
    synchronized (this) {
        queue.enqueue(pendingPost);
        if (!executorRunning) {
            executorRunning = true;
            EventBus.executorService.execute(this);
        }
    }
}

void enqueue(Subscription subscription, Object event) {
    PendingPost pendingPost = PendingPost.obtainPendingPost(subscription, event);
    synchronized (this) {
        queue.enqueue(pendingPost);
        if (!handlerActive) {
            handlerActive = true;
            if (!sendMessage(obtainMessage())) {
                throw new EventBusException("Could not send handler message");
            }
        }
    }
}

public void enqueue(Subscription subscription, Object event) {
    PendingPost pendingPost = PendingPost.obtainPendingPost(subscription, event);
    queue.enqueue(pendingPost);
    EventBus.executorService.execute(this);
}

if (sticky) {
    Object stickyEvent;
    synchronized (stickyEvents) {
        stickyEvent = stickyEvents.get(eventType);
    }
    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());
    }
}