锐客网

  1. 首页 > it技术 > >

EventBus|EventBus 源码分析（下篇）

上篇 EventBus 源码分析（上篇） 说到注册订阅的前半部分，此篇用来分析发送事件到接收事件这个过程。
1. 发送事件 示例：
EventBus.getDefault().post(new RemindBean("2018-02-12","happy"));

post:
/** Posts the given event to the event bus. */ public void post(Object event) { - 1.获取当前线程的postingThreadState 对象 PostingThreadState postingState = currentPostingThreadState.get(); - 2. 获取里面那个事件队列 List eventQueue = postingState.eventQueue; - 3. 将事件添加到队列中去 eventQueue.add(event); - 4. 判断当前的event 是否在 posting if (!postingState.isPosting) { - 5. 是否是主线程 postingState.isMainThread = Looper.getMainLooper() == Looper.myLooper(); postingState.isPosting = true; - 6. 判断是否取消 if (postingState.canceled) { throw new EventBusException("Internal error. Abort state was not reset"); } try { while (!eventQueue.isEmpty()) {//不为空，进入循环 - 7.按照顺序，post一个 remove一个 postSingleEvent(eventQueue.remove(0), postingState); } } finally { postingState.isPosting = false; postingState.isMainThread = false; } } }
PostingThreadState 大概看一眼
final static class PostingThreadState { final List eventQueue = new ArrayList(); boolean isPosting; boolean isMainThread; Subscription subscription; Object event; boolean canceled; }
再就是 postSingleEvent(eventQueue.remove(0), postingState); 方法：
private void postSingleEvent(Object event, PostingThreadState postingState) throws Error { - 1. 获取event的字节码（例如就是：RemindBean.class） Class eventClass = event.getClass(); boolean subscriptionFound = false; if (eventInheritance) {//默认为true - 2. 根据eventClass 的字节码查找 List> eventTypes = lookupAllEventTypes(eventClass); int countTypes = eventTypes.size(); - 3.循环遍历 for (int h = 0; h < countTypes; h++) { Class clazz = eventTypes.get(h); - 4.根据事件，字节码查找订阅者 subscriptionFound |= postSingleEventForEventType(event, postingState, clazz); } } else { subscriptionFound = postSingleEventForEventType(event, postingState, eventClass); } if (!subscriptionFound) { if (logNoSubscriberMessages) { Log.d(TAG, "No subscribers registered for event " + eventClass); } if (sendNoSubscriberEvent && eventClass != NoSubscriberEvent.class && eventClass != SubscriberExceptionEvent.class) { post(new NoSubscriberEvent(this, event)); } } }

postSingleEventForEventType:
private boolean postSingleEventForEventType(Object event, PostingThreadState postingState, Class eventClass) { CopyOnWriteArrayList subscriptions; synchronized (this) { - 1.根据字节码取出subscriptions,还记得我们之前在subscribe这个方法的时候， 把subscrber,subscriberMethod 封装成一个subscription 对象。subscriptions = subscriptionsByEventType.get(eventClass); } if (subscriptions != null && !subscriptions.isEmpty()) { for (Subscription subscription : subscriptions) { - 2. 取出每一个subscription 对象 postingState.event = event; postingState.subscription = subscription; boolean aborted = false; try { - 3. post到相应的线程中回调 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; }

【EventBus|EventBus 源码分析（下篇）】postToSubscription: 根据定义的不同线程，调用相应的方法
private void postToSubscription(Subscription subscription, Object event, boolean isMainThread) { switch (subscription.subscriberMethod.threadMode) { case POSTING://一般没定义的，这个就是post在哪个线程，响应就在哪个线程执行 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); } }

invokeSubscriber:
void invokeSubscriber(Subscription subscription, Object event) { try { - 反射拿到字节码clazz 反射调用方法，就收到消息了 subscription.subscriberMethod.method.invoke(subscription.subscriber, event); } catch (InvocationTargetException e) { handleSubscriberException(subscription, event, e.getCause()); } catch (IllegalAccessException e) { throw new IllegalStateException("Unexpected exception", e); } }

end.

    推荐阅读


    上一篇：一零二四

    下一篇：如何能让对方能更喜欢自己（）