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EventBus 粘性事件，源码解析

2024-08-11 08:27:22   219人阅读

1 Eeventbus 在处理消息通信的时候是比通常的出发办法好用的得，最新使用了eventbus 的粘性事件 首先你需要传递一个消息bean，

 EventBus.getDefault().postSticky(messageStatusResultBean);

2 调用上面的方法 就会把这个objoct 放到里面 

private final Map<Class<?>, Object> stickyEvents;

3 在要处理的地方获取消息bean

  @Subscribe(sticky = true, threadMode = ThreadMode.MAIN)    public void getPushMsg(MessageStatusResultBean messageStatusResultBean) {}

4 粘性事件要收到移除

   EventBus.getDefault().removeStickyEvent(MessageStatusResultBean.class);

 

5 他是如何调用的呢，首先我们会在oncreate的时候做这样的一件事情

  if (!EventBus.getDefault().isRegistered(this))            EventBus.getDefault().register(this);

6 然后我们来看看  register 这个方法 调用了subcribe方法

public void register(Object subscriber) {        Class<?> subscriberClass = subscriber.getClass();        List<SubscriberMethod> subscriberMethods = subscriberMethodFinder.findSubscriberMethods(subscriberClass);        synchronized (this) {            for (SubscriberMethod subscriberMethod : subscriberMethods) {                subscribe(subscriber, subscriberMethod); //调用了subcribe方法
} } }

7 接做看 subscribe 方法

  // Must be called in synchronized block    private void subscribe(Object subscriber, SubscriberMethod subscriberMethod) {     //....        if (subscriberMethod.sticky) {            if (eventInheritance) {                // 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);            }        }    }

8 接下来走到

 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);        }    }

9 接下来就是去处理了，会根据线程模式的不同处理不同的事件 ，在主线程是通过handle来处理的

  @Override    public void handleMessage(Message msg) {        boolean rescheduled = false;        try {            long started = SystemClock.uptimeMillis();            while (true) {                PendingPost pendingPost = queue.poll();                if (pendingPost == null) {                    synchronized (this) {                        // Check again, this time in synchronized                        pendingPost = queue.poll();                        if (pendingPost == null) {                            handlerActive = false;                            return;                        }                    }                }                eventBus.invokeSubscriber(pendingPost);                long timeInMethod = SystemClock.uptimeMillis() - started;                if (timeInMethod >= maxMillisInsideHandleMessage) {                    if (!sendMessage(obtainMessage())) {                        throw new EventBusException("Could not send handler message");                    }                    rescheduled = true;                    return;                }            }        } finally {            handlerActive = rescheduled;        }    }

 

EventBus 粘性事件，源码解析


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