源码阅读--EventBus

使用方法 http://blog.csdn.net/harvic880925/article/details/40660137

1.构造函数

EventBus.getDefault()——————单例模式

public static EventBus getDefault() { if (defaultInstance == null) { synchronized (EventBus.class) { if (defaultInstance == null) { defaultInstance = new EventBus(); } } } return defaultInstance; }

2.注册函数

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

subscriberMethodFinder里面有重要的数据结构METHOD_CACHE，也就是ConcurrentHashMap。那么findSubscriberMethods就好理解了 //————————-遍历该类内部所有方法，然后根据methodName去匹配，匹配成功的封装成SubscriberMethod，最后返回一个List

List<SubscriberMethod> findSubscriberMethods(Class<?> subscriberClass) { List<SubscriberMethod> subscriberMethods = METHOD_CACHE.get(subscriberClass);//------------------------------- if (subscriberMethods != null) { return subscriberMethods; } if (ignoreGeneratedIndex) { subscriberMethods = findUsingReflection(subscriberClass); } else { subscriberMethods = findUsingInfo(subscriberClass); } if (subscriberMethods.isEmpty()) { throw new EventBusException("Subscriber " + subscriberClass + " and its super classes have no public methods with the @Subscribe annotation");//---------------可以看到扫描@Subscribe注解的方法 } else { METHOD_CACHE.put(subscriberClass, subscriberMethods);//------------------------------------------------ return subscriberMethods; } }

再看一下subscribe函数

private void subscribe(Object subscriber, SubscriberMethod subscriberMethod) { Class<?> eventType = subscriberMethod.eventType; Subscription newSubscription = new Subscription(subscriber, subscriberMethod);//----------------------------将SubscriberMethod包装成Subscription CopyOnWriteArrayList<Subscription> subscriptions = subscriptionsByEventType.get(eventType); if (subscriptions == null) { subscriptions = new CopyOnWriteArrayList<>(); subscriptionsByEventType.put(eventType, subscriptions);//---------------------------------Map<Class<?>, CopyOnWriteArrayList<Subscription>> } 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++) { if (i == size || subscriberMethod.priority > subscriptions.get(i).subscriberMethod.priority) { subscriptions.add(i, newSubscription);//-----------------------------将Subscription添加到CopyOnWriteArrayList中保存起来。知道这个，基本也能知道解注册会发生什么 break; } } List<Class<?>> subscribedEvents = typesBySubscriber.get(subscriber); if (subscribedEvents == null) { subscribedEvents = new ArrayList<>(); typesBySubscriber.put(subscriber, subscribedEvents); } subscribedEvents.add(eventType); 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); } } }

3.解注册函数

public synchronized void unregister(Object subscriber) { List<Class<?>> subscribedTypes = typesBySubscriber.get(subscriber); if (subscribedTypes != null) { for (Class<?> eventType : subscribedTypes) { unsubscribeByEventType(subscriber, eventType);//------------------------------ } typesBySubscriber.remove(subscriber); } else { Log.w(TAG, "Subscriber to unregister was not registered before: " + subscriber.getClass()); } } //-----------------------------------------清除subscriptionsByEventType中对应的数据 private void unsubscribeByEventType(Object subscriber, Class<?> eventType) { List<Subscription> subscriptions = subscriptionsByEventType.get(eventType); if (subscriptions != null) { int size = subscriptions.size(); for (int i = 0; i < size; i++) { Subscription subscription = subscriptions.get(i); if (subscription.subscriber == subscriber) { subscription.active = false; subscriptions.remove(i); i--; size--; } } } }

4.发送消息函数

post函数调用postSingleEvent，再调用postSingleEventForEventType

private boolean postSingleEventForEventType(Object event, PostingThreadState postingState, Class<?> eventClass) { CopyOnWriteArrayList<Subscription> subscriptions; synchronized (this) { subscriptions = subscriptionsByEventType.get(eventClass);//------------------------------------根据类名获取subscriptions } if (subscriptions != null && !subscriptions.isEmpty()) { for (Subscription subscription : subscriptions) { postingState.event = event; postingState.subscription = subscription; boolean aborted = false; try { 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; } //-------------------------------------------------------------------根据方法名调用不同的case函数，我们这里是post 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); } } void invokeSubscriber(Subscription subscription, Object event) { try { subscription.subscriberMethod.method.invoke(subscription.subscriber, event);//--------------------------------反射机制调用相关方法 } catch (InvocationTargetException e) { handleSubscriberException(subscription, event, e.getCause()); } catch (IllegalAccessException e) { throw new IllegalStateException("Unexpected exception", e); } }

5.CopyOnWriteArrayList

构造函数：

public CopyOnWriteArrayList() { setArray(new Object[0]); } public CopyOnWriteArrayList(Collection<? extends E> c) { Object[] elements = c.toArray(); // c.toArray might (incorrectly) not return Object[] (see 6260652) if (elements.getClass() != Object[].class) elements = Arrays.copyOf(elements, elements.length, Object[].class); setArray(elements); } public CopyOnWriteArrayList(E[] toCopyIn) { setArray(Arrays.copyOf(toCopyIn, toCopyIn.length, Object[].class)); } final void setArray(Object[] a) { array = a; } private volatile transient Object[] array;//-----------------------------------------不会被序列化

get函数：

public E get(int index) { return get(getArray(), index); } private E get(Object[] a, int index) { return (E) a[index]; }

add函数：（写时复制）

public boolean add(E e) { final ReentrantLock lock = this.lock; lock.lock(); try { Object[] elements = getArray(); int len = elements.length; Object[] newElements = Arrays.copyOf(elements, len + 1); newElements[len] = e; setArray(newElements); return true; } finally { lock.unlock(); } }

Java中的ReentrantLock和synchronized两种锁定机制的对比：http://blog.csdn.net/fw0124/article/details/6672522