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EventBus类
public class EventBus {
/** Log tag, apps may override it. */
public static String TAG = "EventBus";
//单实例EventBus，默认
static volatile EventBus defaultInstance;
private static final EventBusBuilder DEFAULT_BUILDER = new EventBusBuilder();
//此事件类型 ：此事件和它的父类，接口组成的集合
private static final Map<Class<?>, List<Class<?>>> eventTypesCache = new HashMap<>();
//此事件类型 ：订阅这个事件的所有订阅者信息
private final Map<Class<?>, CopyOnWriteArrayList<Subscription>> subscriptionsByEventType;
//订阅者 ：它订阅的所有事件类型
private final Map<Object, List<Class<?>>> typesBySubscriber;
//sticky事件类型 ：sticky事件
private final Map<Class<?>, Object> stickyEvents;
//在当前线程存储数据：PostingThreadState(发射线程状态)
private final ThreadLocal<PostingThreadState> currentPostingThreadState = new ThreadLocal<PostingThreadState>() {
@Override
protected PostingThreadState initialValue() {
return new PostingThreadState();
}
};
// @Nullable
private final MainThreadSupport mainThreadSupport;
// 发射器
private final Poster mainThreadPoster; //若支持主线程则创建HandlerPoster
private final BackgroundPoster backgroundPoster;
private final AsyncPoster asyncPoster;
//订阅方法查找
private final SubscriberMethodFinder subscriberMethodFinder;
//线程池
private final ExecutorService executorService;
private final boolean throwSubscriberException;
private final boolean logSubscriberExceptions;
private final boolean logNoSubscriberMessages;
private final boolean sendSubscriberExceptionEvent;
private final boolean sendNoSubscriberEvent;
private final boolean eventInheritance;
//注解数量
private final int indexCount;
private final Logger logger;
/** 单实例 */
public static EventBus getDefault() {
EventBus instance = defaultInstance;
if (instance == null) {
synchronized (EventBus.class) {
instance = EventBus.defaultInstance;
if (instance == null) {
instance = EventBus.defaultInstance = new EventBus();
}
}
}
return instance;
}
public static EventBusBuilder builder() {
return new EventBusBuilder();
}
/** 清除缓存*/
public static void clearCaches() {
SubscriberMethodFinder.clearCaches(); //清除订阅此事件的所有订阅方法
eventTypesCache.clear(); //清除此订阅方法
}
/** 创建一个新的EventBus，调用EventBus(EventBusBuilder builder)*/
public EventBus() {
this(DEFAULT_BUILDER);
}
EventBus(EventBusBuilder builder) {
logger = builder.getLogger();
subscriptionsByEventType = new HashMap<>();
typesBySubscriber = new HashMap<>();
stickyEvents = new ConcurrentHashMap<>();
mainThreadSupport = builder.getMainThreadSupport();
mainThreadPoster = mainThreadSupport != null ? mainThreadSupport.createPoster(this) : null;
backgroundPoster = new BackgroundPoster(this);
asyncPoster = new AsyncPoster(this);
indexCount = builder.subscriberInfoIndexes != null ? builder.subscriberInfoIndexes.size() : 0;
subscriberMethodFinder = new SubscriberMethodFinder(builder.subscriberInfoIndexes,
builder.strictMethodVerification, builder.ignoreGeneratedIndex);
logSubscriberExceptions = builder.logSubscriberExceptions;
logNoSubscriberMessages = builder.logNoSubscriberMessages;
sendSubscriberExceptionEvent = builder.sendSubscriberExceptionEvent;
sendNoSubscriberEvent = builder.sendNoSubscriberEvent;
throwSubscriberException = builder.throwSubscriberException;
eventInheritance = builder.eventInheritance;
executorService = builder.executorService;
}
/**
* 注册接收事件的Activity/Fragment为Subscribers到EventBus中
* 在订阅者中通过@Subscribe的方式注解订阅事件的方法，可以指定线程模式，级别，sticky
* The {@link Subscribe} annotation also allows configuration like {@link
* ThreadMode} and priority.
*/
public void register(Object subscriber) {
Class<?> subscriberClass = subscriber.getClass();
//查找注册的Activity/Fragment中所有订阅方法，遍历
List<SubscriberMethod> subscriberMethods = subscriberMethodFinder.findSubscriberMethods(subscriberClass);
synchronized (this) {
for (SubscriberMethod subscriberMethod : subscriberMethods) {
subscribe(subscriber, subscriberMethod);
}
}
}
// Must be called in synchronized block
private void subscribe(Object subscriber, SubscriberMethod subscriberMethod) {
Class<?> eventType = subscriberMethod.eventType;
//封装为一个新的订阅者信息
Subscription newSubscription = new Subscription(subscriber, subscriberMethod);
//订阅此事件的所有订阅者信息集合
CopyOnWriteArrayList<Subscription> subscriptions = subscriptionsByEventType.get(eventType);
//若集合为空，创建集合，添加这个新的newSubscription到集合
if (subscriptions == null) {
subscriptions = new CopyOnWriteArrayList<>();
subscriptionsByEventType.put(eventType, subscriptions);
} else {
//若集合已存在这个订阅，你这就是再次订阅了，多此一举，抛出异常
if (subscriptions.contains(newSubscription)) {
throw new EventBusException("Subscriber " + subscriber.getClass() + " already registered to event "
+ eventType);
}
}
//将新的订阅者信息newSubscription插入集合，按级别插入，要么就是最后一个位置
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);
break;
}
}
//此新的订阅者Activity/Fragment订阅的所有事件类型集合
List<Class<?>> subscribedEvents = typesBySubscriber.get(subscriber);
if (subscribedEvents == null) {
subscribedEvents = new ArrayList<>();
typesBySubscriber.put(subscriber, subscribedEvents);
}
//存储新的订阅者Activity/Fragment订阅的事件
subscribedEvents.add(eventType);
//若订阅了sticky
if (subscriberMethod.sticky) {
//事件有父类或接口
if (eventInheritance) {
//sticky事件类型的set集合，
Set<Map.Entry<Class<?>, Object>> entries = stickyEvents.entrySet();
for (Map.Entry<Class<?>, Object> entry : entries) {
//一个事件类型
Class<?> candidateEventType = entry.getKey();
//若订阅的事件类型eventType是candidateEventType的父类或接口
if (eventType.isAssignableFrom(candidateEventType)) {
Object stickyEvent = entry.getValue();
//检查是否在主线程发送给订阅者
checkPostStickyEventToSubscription(newSubscription, stickyEvent);
}
}
} else {
//sticky事件无父类或接口，直接获取sticky事件
Object stickyEvent = stickyEvents.get(eventType);
checkPostStickyEventToSubscription(newSubscription, stickyEvent);
}
}
}
//检查是否在主线程发送给订阅者
private void checkPostStickyEventToSubscription(Subscription newSubscription, Object stickyEvent) {
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, isMainThread());
}
}
//指定线程模式发送给订阅者
private void postToSubscription(Subscription subscription, Object event, boolean isMainThread) {
switch (subscription.subscriberMethod.threadMode) {
case POSTING:
//不论在那个线程则直接在当前线程订阅
invokeSubscriber(subscription, event);
break;
case MAIN:
if (isMainThread) {
//主线程则直接反射调用
invokeSubscriber(subscription, event);
} else {
//普通发射
mainThreadPoster.enqueue(subscription, event);
}
break;
case MAIN_ORDERED:
if (mainThreadPoster != null) {
mainThreadPoster.enqueue(subscription, event);
} else {
// temporary: technically not correct as poster not decoupled from subscriber
invokeSubscriber(subscription, event);
}
break;
case BACKGROUND:
if (isMainThread) {
//若当前为主线程，则启用后台线程
backgroundPoster.enqueue(subscription, event);
} else {
//若不是主线程则直接在当前线程订阅
invokeSubscriber(subscription, event);
}
break;
case ASYNC:
//新启动一个线程异步订阅
asyncPoster.enqueue(subscription, event);
break;
default:
throw new IllegalStateException("Unknown thread mode: " + subscription.subscriberMethod.threadMode);
}
}
private boolean isMainThread() {
return mainThreadSupport != null ? mainThreadSupport.isMainThread() : true;
}
public synchronized boolean isRegistered(Object subscriber) {
return typesBySubscriber.containsKey(subscriber);
}
/** ondestory中解注册 */
public synchronized void unregister(Object subscriber) {
//此订阅者中的所有订阅事件类型
List<Class<?>> subscribedTypes = typesBySubscriber.get(subscriber);
if (subscribedTypes != null) {
for (Class<?> eventType : subscribedTypes) {
//从 事件类型 ：所有订阅者 集合中移除这个订阅者
unsubscribeByEventType(subscriber, eventType);
}
//从 订阅者；其订阅的事件 集合中移除key：订阅者
typesBySubscriber.remove(subscriber);
} else {
logger.log(Level.WARNING, "Subscriber to unregister was not registered before: " + subscriber.getClass());
}
}
/** 从 事件类型 ：所有订阅者 集合中移除这个订阅者 */
private void unsubscribeByEventType(Object subscriber, Class<?> eventType) {
//订阅此事件的所有订阅者集合
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);
//从中移除次订阅者
if (subscription.subscriber == subscriber) {
subscription.active = false;
subscriptions.remove(i);
i--;
size--;
}
}
}
}
/** 发送事件到EventBus */
public void post(Object event) {
PostingThreadState postingState = currentPostingThreadState.get(); //发送事件状态
List<Object> eventQueue = postingState.eventQueue; //事件队列
eventQueue.add(event); //添加事件到队列
//若当前没有在发送
if (!postingState.isPosting) {
postingState.isMainThread = isMainThread();
postingState.isPosting = true;
//若发送状态取消，抛出异常
if (postingState.canceled) {
throw new EventBusException("Internal error. Abort state was not reset");
}
try {
//只要队列不为空，就发送
while (!eventQueue.isEmpty()) {
postSingleEvent(eventQueue.remove(0), postingState);
}
} finally {
postingState.isPosting = false;
postingState.isMainThread = false;
}
}
}
//给所有订阅了此事件的订阅者发送事件
private void postSingleEvent(Object event, PostingThreadState postingState) throws Error {
Class<?> eventClass = event.getClass();
boolean subscriptionFound = false;
if (eventInheritance) {
//查找此事件的类对象，包括它的父类和接口，添加到eventTypes
List<Class<?>> eventTypes = lookupAllEventTypes(eventClass);
int countTypes = eventTypes.size();
for (int h = 0; h < countTypes; h++) {
Class<?> clazz = eventTypes.get(h);
subscriptionFound |= postSingleEventForEventType(event, postingState, clazz);
}
} else {
subscriptionFound = postSingleEventForEventType(event, postingState, eventClass);
}
if (!subscriptionFound) {
if (logNoSubscriberMessages) {
logger.log(Level.FINE, "No subscribers registered for event " + eventClass);
}
if (sendNoSubscriberEvent && eventClass != NoSubscriberEvent.class &&
eventClass != SubscriberExceptionEvent.class) {
post(new NoSubscriberEvent(this, event));
}
}
}
//给所有订阅了此事件的订阅者发送事件
private boolean postSingleEventForEventType(Object event, PostingThreadState postingState, Class<?> eventClass) {
//可并发读写
CopyOnWriteArrayList<Subscription> subscriptions;
synchronized (this) {
//获取此事件的所有订阅者信息集合
subscriptions = subscriptionsByEventType.get(eventClass);
}
if (subscriptions != null && !subscriptions.isEmpty()) {
for (Subscription subscription : subscriptions) {
postingState.event = event;
postingState.subscription = subscription;
boolean aborted = false; //是否拦截发送
try {
//发送给订阅者
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;
}
/** 查找此事件的类对象，包括它的父类和接口 */
private static List<Class<?>> lookupAllEventTypes(Class<?> eventClass) {
//此事件类型 ：此事件和它的父类，接口组成的集合
synchronized (eventTypesCache) {
List<Class<?>> eventTypes = eventTypesCache.get(eventClass);
//若为空，创建集合，存储当前的事件集合
if (eventTypes == null) {
eventTypes = new ArrayList<>();
//当前事件
Class<?> clazz = eventClass;
while (clazz != null) {
//第一次，添加eventClass
eventTypes.add(clazz);
//递归查询多有接口，包括接口的接口，添加
addInterfaces(eventTypes, clazz.getInterfaces());
//向上查询父类，添加
clazz = clazz.getSuperclass();
}
eventTypesCache.put(eventClass, eventTypes);
}
return eventTypes;
}
}
/** 递归查询多有接口，包括接口的接口，添加 */
static void addInterfaces(List<Class<?>> eventTypes, Class<?>[] interfaces) {
for (Class<?> interfaceClass : interfaces) {
if (!eventTypes.contains(interfaceClass)) {
eventTypes.add(interfaceClass);
addInterfaces(eventTypes, interfaceClass.getInterfaces());
}
}
}
/** 取消发送事件 */
public void cancelEventDelivery(Object event) {
//当前发送线程状态
PostingThreadState postingState = currentPostingThreadState.get();
if (!postingState.isPosting) {
throw new EventBusException(
"This method may only be called from inside event handling methods on the posting thread");
} else if (event == null) {
throw new EventBusException("Event may not be null");
} else if (postingState.event != event) {
throw new EventBusException("Only the currently handled event may be aborted");
} else if (postingState.subscription.subscriberMethod.threadMode != POSTING) {
throw new EventBusException(" event handlers may only abort the incoming event");
}
postingState.canceled = true;
}
/** 发送事件，缓存这个事件到stickyEvents，若有订阅者在之后订阅，还可收到stickyEvents中离
* 订阅者最近的一个事件*/
public void postSticky(Object event) {
synchronized (stickyEvents) {
stickyEvents.put(event.getClass(), event);
}
// Should be posted after it is putted, in case the subscriber wants to remove immediately
post(event);
}
/** 获取指定类型sticky事件 */
public <T> T getStickyEvent(Class<T> eventType) {
synchronized (stickyEvents) {
return eventType.cast(stickyEvents.get(eventType));
}
}
/** 移除指定类型sticky事件*/
public <T> T removeStickyEvent(Class<T> eventType) {
synchronized (stickyEvents) {
return eventType.cast(stickyEvents.remove(eventType));
}
}
/** 移除指定sticky事件，需判断它们是否有相同的class属性*/
public boolean removeStickyEvent(Object event) {
synchronized (stickyEvents) {
Class<?> eventType = event.getClass();
//以类型查找事件，看是否是同一个事件
Object existingEvent = stickyEvents.get(eventType);
if (event.equals(existingEvent)) {
stickyEvents.remove(eventType);
return true;
} else {
return false;
}
}
}
/**移除所有sticky事件*/
public void removeAllStickyEvents() {
synchronized (stickyEvents) {
stickyEvents.clear();
}
}
/** 是否有此事件的订阅者*/
public boolean hasSubscriberForEvent(Class<?> eventClass) {
//查找此事件的类对象，包括它的父类和接口
List<Class<?>> eventTypes = lookupAllEventTypes(eventClass);
if (eventTypes != null) {
int countTypes = eventTypes.size();
for (int h = 0; h < countTypes; h++) {
Class<?> clazz = eventTypes.get(h);
CopyOnWriteArrayList<Subscription> subscriptions;
synchronized (this) {
//订阅了此事件（包括它的父类，接口）的所有订阅者
subscriptions = subscriptionsByEventType.get(clazz);
}
if (subscriptions != null && !subscriptions.isEmpty()) {
return true;
}
}
}
return false;
}
/**
* 如果订阅为可发送状态，则调用订阅方。跳过订阅可以防止{@link #unregister(Object)}和事件交付之间的竞争条件。
* 否则，事件可能在订阅者未注册后交付。这对于绑定到活动或片段的活动周期的主线程交付和注册尤其重要。
*/
void invokeSubscriber(PendingPost pendingPost) {
Object event = pendingPost.event;
Subscription subscription = pendingPost.subscription;
//先存储即将发送事件pendingPost，释放事件池中的它
PendingPost.releasePendingPost(pendingPost);
if (subscription.active) {
invokeSubscriber(subscription, event);
}
}
/** 反射调用订阅者的订阅方法进行订阅*/
void invokeSubscriber(Subscription subscription, Object event) {
try {
//反射调用subscriber的订阅方法method，订阅的事件为参数event
subscription.subscriberMethod.method.invoke(subscription.subscriber, event);
} catch (InvocationTargetException e) {
handleSubscriberException(subscription, event, e.getCause());
} catch (IllegalAccessException e) {
throw new IllegalStateException("Unexpected exception", e);
}
}
private void handleSubscriberException(Subscription subscription, Object event, Throwable cause) {
if (event instanceof SubscriberExceptionEvent) {
if (logSubscriberExceptions) {
// Don't send another SubscriberExceptionEvent to avoid infinite event recursion, just log
logger.log(Level.SEVERE, "SubscriberExceptionEvent subscriber " + subscription.subscriber.getClass()
+ " threw an exception", cause);
SubscriberExceptionEvent exEvent = (SubscriberExceptionEvent) event;
logger.log(Level.SEVERE, "Initial event " + exEvent.causingEvent + " caused exception in "
+ exEvent.causingSubscriber, exEvent.throwable);
}
} else {
if (throwSubscriberException) {
throw new EventBusException("Invoking subscriber failed", cause);
}
if (logSubscriberExceptions) {
logger.log(Level.SEVERE, "Could not dispatch event: " + event.getClass() + " to subscribing class "
+ subscription.subscriber.getClass(), cause);
}
if (sendSubscriberExceptionEvent) {
SubscriberExceptionEvent exEvent = new SubscriberExceptionEvent(this, cause, event,
subscription.subscriber);
post(exEvent);
}
}
}
/** 在ThreadLocal存储的数据类 */
final static class PostingThreadState {
final List<Object> eventQueue = new ArrayList<>(); //事件队列
boolean isPosting; //是否正在发送事件
boolean isMainThread; //是否主线程
Subscription subscription; //订阅者信息
Object event; //发送的事件
boolean canceled; //是否取消发送
}
ExecutorService getExecutorService() {
return executorService;
}
/**
* For internal use only.
*/
public Logger getLogger() {
return logger;
}
// Just an idea: we could provide a callback to post() to be notified, an alternative would be events, of course...
/* public */interface PostCallback {
void onPostCompleted(List<SubscriberExceptionEvent> exceptionEvents);
}
@Override
public String toString() {
return "EventBus[indexCount=" + indexCount + ", eventInheritance=" + eventInheritance + "]";
}
}