上篇文章介绍了EventBus注册流程, 本篇文章简介EventBus发送事件的流程

EventBus源码(一)

1.发送事件Demo的代码

EventBus.getDefault().post("我是小名同学");

2.源码流程图

image.png

2.1源码流程

  /** Posts the given event to the event bus. */
    public void post(Object event) {
     //获取当前线程的一个状态 类型是 ThreadLoacal 
        PostingThreadState postingState = currentPostingThreadState.get();
    //获取事件队列
        List<Object> eventQueue = postingState.eventQueue;
    //加入到事件队列中
        eventQueue.add(event);
    //是否正在处理事件中
        if (!postingState.isPosting) {
        //是否为主线程
            postingState.isMainThread = isMainThread();
            postingState.isPosting = true;
            if (postingState.canceled) {
                throw new EventBusException("Internal error. Abort state was not reset");
            }
            try {
              //while 队列 发送消息
                while (!eventQueue.isEmpty()) {
                    postSingleEvent(eventQueue.remove(0), postingState);
                }
            } finally {
                postingState.isPosting = false;
                postingState.isMainThread = false;
            }
        }
    }

post事件,获取到当前的线程的信息PostingThreadState, 包括当前线程的事件集合,状态,以及subscription信息,在进行遍历事件队列,通过 postSingleEventForEventType逐步对每个事件进行处理(省略postSingleEvent方法)

private boolean postSingleEventForEventType(Object event, PostingThreadState postingState, Class<?> eventClass) {
        CopyOnWriteArrayList<Subscription> subscriptions;
        synchronized (this) {
          //根据event类型 获取到 subscription集合
            subscriptions = subscriptionsByEventType.get(eventClass);
        }
        if (subscriptions != null && !subscriptions.isEmpty()) {
            //遍历subscription集合, 并把事件写入到postingState中
            for (Subscription subscription : subscriptions) {
                postingState.event = event;
                postingState.subscription = subscription;
                boolean aborted = false;
                try {
                    //通过这个方法进行发送事件
                    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;
    }

 //根据subscription获取到SubscribeMethod信息, 并且可以获取到 注解的 线程类型
  private void postToSubscription(Subscription subscription, Object event, boolean isMainThread) {
        switch (subscription.subscriberMethod.threadMode) {
            case POSTING:]
               //统一线程执行 接受订阅事件
                invokeSubscriber(subscription, event);
                break;
            case MAIN:
              //主线程执行 判断是否在主线程 如果在直接执行,不在通过Handler进行线程调度
                if (isMainThread) {
                    invokeSubscriber(subscription, event);
                } else {
                    mainThreadPoster.enqueue(subscription, event);
                }
                break;
            case MAIN_ORDERED:
              //主线程非阻塞的
                if (mainThreadPoster != null) {
                    mainThreadPoster.enqueue(subscription, event);
                } else {
                    // temporary: technically not correct as poster not decoupled from subscriber
                    invokeSubscriber(subscription, event);
                }
                break;
            case BACKGROUND:
             //发送 和 订阅 可以 处于同一个子线程中,如果发送在主线程,订阅需要重新开启新线程进行处理
                if (isMainThread) {
                    backgroundPoster.enqueue(subscription, event);
                } else {
                    invokeSubscriber(subscription, event);
                }
                break;
            case ASYNC:
             //订阅者开启新的线程处理事件
                asyncPoster.enqueue(subscription, event);
                break;
            default:
                throw new IllegalStateException("Unknown thread mode: " + subscription.subscriberMethod.threadMode);
        }
    }

  //执行订阅方法
    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);
        }
    }

以上就是EventBus的post流程.