1. EventBus用法
// EventBus的注册
EventBus.getDefault().register(this);
// EventBus的解除注册
EventBus.getDefault().unregister(this);
// 发送事件
EventBus.getDefault().post(new Object());
// 接收事件
@Subscribe(threadMode = ThreadMode.MAIN)
public void onOtherDisplay(Object obj) {
}
2. EventBus实例化
public static EventBus getDefault() {
if (defaultInstance == null) {
synchronized (EventBus.class) {
if (defaultInstance == null) {
defaultInstance = new EventBus();
}
}
}
return defaultInstance;
}
EventBus(EventBusBuilder builder) {
......
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);
......
executorService = builder.executorService;
}
- 采用双重校验锁的单例模式来获取EventBus的实例
- **subscriptionsByEventType:**HashMap<事件类型,Subscription集合(注册类与订阅方法)>
- **typesBySubscriber:**HashMap<存储key的注册类,事件类型集合的HashMap>,判断某个对象是否注册过,防止重复注册
- **mainThreadPoster:**将线程模型为MAIN和Main_ordere的事件加入队列
- **backgroundPoster:**将线程模型为background的事件加入到队列
- **asyncPoster:**将线程模型为ASYNC的事件加入到队列
3. EventBus的注册
- 从缓存中查找该注册类的订阅方法,缓存中有,直接返回,缓存中无,查找所有订阅方法,放入缓存中
- 通过反射获取注册类中的所有方法,循环遍历这些方法,获取方法上的注解,获取方法的第一个参数为事件类型、线程模式、将方法、事件模型、线程模型、优先级、是否是粘性时间封装到SubscriberMethod对象,然后添加到FindState类中subscriberMethods中
- 将注册类与订阅方法封装到Subscription中, 按照事件的优先级排序,subscriptions,这个后续会解除注册
- subscriptionByEventType: 获取事件类型eventType,通过eventType查找subscriptionByEventType查找是否已有SubScrition集合,没有就创建加入subscriptionByEventType
- typesBySubscriber : 一个存储 key 为注册类(对应使用示例中的 EventBusFirstActivity),value 为事件类型集合的 HashMap
- 如果是粘性事件是,从stickEvents中取出,进行处理,根据线程模式判断是否需要切换线程,不需要则直接通过反射调用订阅方法;需要则通过 Handler 或线程池切换到指定线程再执行
public void register(Object subscriber) {
Class<?> subscriberClass = subscriber.getClass();
List<SubscriberMethod> subscriberMethods = subscriberMethodFinder.findSubscriberMethods(subscriberClass); // 见【1】
synchronized (this) {
// 见【2】
for (SubscriberMethod subscriberMethod : subscriberMethods) {
subscribe(subscriber, subscriberMethod);
}
}
}
【1】findSubscriberMethods()
private static final Map<Class<?>, List<SubscriberMethod>> METHOD_CACHE = new ConcurrentHashMap<>();
private final boolean ignoreGeneratedIndex;
List<SubscriberMethod> findSubscriberMethods(Class<?> subscriberClass) {
// 从METHOD_CACHE中查找是否已经缓存了该注册类上的订阅方法
List<SubscriberMethod> subscriberMethods = METHOD_CACHE.get(subscriberClass);
if (subscriberMethods != null) {
return subscriberMethods;
}
if (ignoreGeneratedIndex) {
subscriberMethods = findUsingReflection(subscriberClass);
} else {
// 查找所有的订阅方法
subscriberMethods = findUsingInfo(subscriberClass);// 见【3】
}
if (subscriberMethods.isEmpty()) {
throw new EventBusException("Subscriber " + subscriberClass
+ " and its super classes have no public methods with the @Subscribe annotation");
} else {
// 如果查找所有的订阅方法缓存到METHOD_CACHE集合中
METHOD_CACHE.put(subscriberClass, subscriberMethods);
return subscriberMethods;
}
}
总结:
- 从缓存中查找该注册类的订阅方法,缓存中有,直接返回
- 缓存中无,查找所有订阅方法,放入缓存中
【3】findUsingInfo()
private List<SubscriberMethod> findUsingInfo(Class<?> subscriberClass) {
// 通过FindState用来辅助查订阅方法
FindState findState = prepareFindState();
findState.initForSubscriber(subscriberClass);
while (findState.clazz != null) {
findState.subscriberInfo = getSubscriberInfo(findState);
if (findState.subscriberInfo != null) {
SubscriberMethod[] array = findState.subscriberInfo.getSubscriberMethods();
for (SubscriberMethod subscriberMethod : array) {
if (findState.checkAdd(subscriberMethod.method, subscriberMethod.eventType)) {
findState.subscriberMethods.add(subscriberMethod);
}
}
} else {
// 通过反射获取注册类总的所有方法
findUsingReflectionInSingleClass(findState);// 见【5】
}
findState.moveToSuperclass();
}
return getMethodsAndRelease(findState);
}
【5】findUsingReflectionInSingleClass()
private void findUsingReflectionInSingleClass(FindState findState) {
Method[] methods;
try {
// 反射获取注册类中所有的方法
methods = findState.clazz.getDeclaredMethods();
} catch (Throwable th) {
// 反射获取注册类中的所有方法
methods = findState.clazz.getMethods();
findState.skipSuperClasses = true;
}
// 循环遍历所有的方法
for (Method method : methods) {
int modifiers = method.getModifiers();
if ((modifiers & Modifier.PUBLIC) != 0 && (modifiers & MODIFIERS_IGNORE) == 0) {
Class<?>[] parameterTypes = method.getParameterTypes();
if (parameterTypes.length == 1) {
// 获取方法上的注解
Subscribe subscribeAnnotation = method.getAnnotation(Subscribe.class);
if (subscribeAnnotation != null) {
// 获取方法上第一个参数,即事件类型
Class<?> eventType = parameterTypes[0];
if (findState.checkAdd(method, eventType)) {
// 获取线程模式
ThreadMode threadMode = subscribeAnnotation.threadMode();
// 将方法、事件模型、线程模型、优先级、是否是粘性时间封装到SubscriberMethod对象,然后添加到FindState类中subscriberMethods中
findState.subscriberMethods.add(new SubscriberMethod(method, eventType, threadMode,
subscribeAnnotation.priority(), subscribeAnnotation.sticky()));
}
}
}
.........
}
}
总结:
通过反射获取注册类中的所有方法,循环遍历这些方法,获取方法上的注解,获取方法的第一个参数为事件类型、线程模式、将方法、事件模型、线程模型、优先级、是否是粘性时间封装到SubscriberMethod对象,然后添加到FindState类中subscriberMethods中
【2】Subscribe()
private void subscribe(Object subscriber, SubscriberMethod subscriberMethod) {
// 获取事件类型
Class<?> eventType = subscriberMethod.eventType;
// 将注册类与订阅方法封装到Subscription中
Subscription newSubscription = new Subscription(subscriber, subscriberMethod);
// 通过eventType查找subscriptionByEventType查找是否已有SubScrition集合,没有就创建加入subscriptionByEventType
CopyOnWriteArrayList<Subscription> subscriptions = subscriptionsByEventType.get(eventType);
if (subscriptions == null) {
subscriptions = new CopyOnWriteArrayList<>();
subscriptionsByEventType.put(eventType, subscriptions);
} else {
........
}
// 根据订阅的类中的newSubscription中的优先级加入到subscriptions
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;
}
}
// 将typesBySubscriber 是一个存储 key 为注册类(对应使用示例中的 EventBusFirstActivity),value 为事件类型集合的 HashMap
List<Class<?>> subscribedEvents = typesBySubscriber.get(subscriber);
if (subscribedEvents == null) {
subscribedEvents = new ArrayList<>();
typesBySubscriber.put(subscriber, subscribedEvents);
}
subscribedEvents.add(eventType);
// 后续粘性事件相关逻辑,如果是粘性事件,postToSubscription(newSubscription, stickyEvent, isMainThread())
if (subscriberMethod.sticky) {
if (eventInheritance) {
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);
}
}
}
总结:
- 将注册类与订阅方法封装到Subscription中
- 按照事件的优先级排序,subscriptions
- subscriptionByEventType: 获取事件类型eventType,通过eventType查找subscriptionByEventType查找是否已有SubScrition集合,没有就创建加入subscriptionByEventType
- typesBySubscriber : 一个存储 key 为注册类(对应使用示例中的 EventBusFirstActivity),value 为事件类型集合的 HashMap
- 如果是粘性事件是,从stickEvents中取出,进行处理
4. EventBus的解除注册
注册的时候使用subsciptionByEventType集合中保存了所有的订阅方法信息,使用typesBySubscriber集合保存了所有的事件类型。解除绑定的时候移除这两个集合中保存的内容
public synchronized void unregister(Object subscriber) {
// 根据注册类获取typesBySubscriber集合中保存的事件类型
List<Class<?>> subscribedTypes = typesBySubscriber.get(subscriber);
if (subscribedTypes != null) {
for (Class<?> eventType : subscribedTypes) {
unsubscribeByEventType(subscriber, eventType); // 见【6】
}
// 移除 typeBySubcriber中保存的事件类型集合
typesBySubscriber.remove(subscriber);
} else {
logger.log(Level.WARNING, "Subscriber to unregister was not registered before: " + subscriber.getClass());
}
}
【6】unsubscribeByEventType(subscriber, eventType)
private void unsubscribeByEventType(Object subscriber, Class<?> eventType) {
// 根据事件类型获取subScriptionByEventType集合中保存的Subscription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);
if (subscription.subscriber == subscriber) {
subscription.active = false;
// 从subscription集合中移除
subscriptions.remove(i);
i--;
size--;
}
}
}
}
5. 发送事件post
- 主要是从事件队列中取出一个事件进行发送,所有事件类型,包括当前事件、父类和接口中的事件,如果没有找到订阅者,发送NoSubscriberEvent()事件 从 subscriptionsByEventType 集合中取出所有订阅方法,然后根据线程模式判断是否需要切换线程,不需要则直接通过反射调用订阅方法;需要则通过 Handler 或线程池切换到指定线程再执行。
private final ThreadLocal<PostingThreadState> currentPostingThreadState = new ThreadLocal<PostingThreadState>() {
@Override
protected PostingThreadState initialValue() {
return new PostingThreadState();
}
};
public void post(Object event) {
// currentPostingThreadState是一个ThreadLocal对象,里面保存了PostingThreadState对象,
PostingThreadState postingState = currentPostingThreadState.get();
List<Object> eventQueue = postingState.eventQueue;
eventQueue.add(event);
if (!postingState.isPosting) {
postingState.isMainThread = isMainThread();
postingState.isPosting = true;
if (postingState.canceled) {
throw new EventBusException("Internal error. Abort state was not reset");
}
try {
while (!eventQueue.isEmpty()) {
postSingleEvent(eventQueue.remove(0), postingState); // 见【7】
}
} finally {
postingState.isPosting = false;
postingState.isMainThread = false;
}
}
}
【7】postSingleEvent()
private void postSingleEvent(Object event, PostingThreadState postingState) throws Error {
Class<?> eventClass = event.getClass();
// 是否找到订阅者
boolean subscriptionFound = false;
//(1)表示是否需要发送父类与接口中的事件
if (eventInheritance) {
//(2)查找所有事件类型,包括当前事件、父类和接口中的事件。
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); // 见【8】
}
} else {
// 根据事件类型只发送当前注册类的事件,忽略父类以及接口。
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) {
//(5)没有找到订阅者,发送一个 NoSubscriberEvent 事件
post(new NoSubscriberEvent(this, event));
}
}
}
【8】postSingleEventForEventType()
private boolean postSingleEventForEventType(Object event, PostingThreadState postingState, Class<?> eventClass) {
CopyOnWriteArrayList<Subscription> subscriptions;
synchronized (this) {
// 从subscriptionsByEventType集合中取出之前注册的时候保存的SubScription集合,然后遍历集合拿到SubScription
subscriptions = subscriptionsByEventType.get(eventClass);
}
if (subscriptions != null && !subscriptions.isEmpty()) {
for (Subscription subscription : subscriptions) {
postingState.event = event;
postingState.subscription = subscription;
boolean aborted = false;
try {
postToSubscription(subscription, event, postingState.isMainThread); // 见【9】
aborted = postingState.canceled;
} finally {
postingState.event = null;
postingState.subscription = null;
postingState.canceled = false;
}
if (aborted) {
break;
}
}
return true;
}
return false;
}
【9】postToSubscription()
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); // 见【10】
} else {
mainThreadPoster.enqueue(subscription, event);
}
break;
case MAIN_ORDERED:
if (mainThreadPoster != null) {
mainThreadPoster.enqueue(subscription, event);
} else {
invokeSubscriber(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);
}
}
根据不同线程模型来决定在哪个线程执行订阅方法
【10】invokeSubscriber()
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);
}
}
直接通过反射调用
Main
如果线程模式是 MAIN,那么在主线程发送事件,则在主线程执行订阅方法;否则先将事件加入到队列中,然后通过 Handler 切换到主线程再执行invokeSubscriber()方法
public class HandlerPoster extends Handler implements Poster {
private final PendingPostQueue queue;
public void enqueue(Subscription subscription, Object event) {
PendingPost pendingPost = PendingPost.obtainPendingPost(subscription, event);
synchronized (this) {
queue.enqueue(pendingPost);
if (!handlerActive) {
handlerActive = true;
if (!sendMessage(obtainMessage())) {
throw new EventBusException("Could not send handler message");
}
}
}
}
@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) {
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;
}
}
}
MAIN_ORDERED
如果线程模式是 MAIN_ORDERED,那么无论在哪个线程发送事件,都会先将事件加入到队列中,然后通过 Handler 切换到主线程再执行
BACKGROUND
subscription 和 event 封装成一个 PendingPost 对象,然后加入到队列中。不同的是这里不是使用 Handler 发送消息,而是通过线程池去执行。所以,如果线程模式是 BACKGROUND,那么在子线程发送事件,则在子线程执行订阅方法,否则先将事件加入到队列中,然后通过线程池去执行
final class BackgroundPoster implements Runnable, Poster {
private final PendingPostQueue queue;
private final EventBus eventBus;
private volatile boolean executorRunning;
BackgroundPoster(EventBus eventBus) {
this.eventBus = eventBus;
queue = new PendingPostQueue();
}
public void enqueue(Subscription subscription, Object event) {
PendingPost pendingPost = PendingPost.obtainPendingPost(subscription, event);
synchronized (this) {
queue.enqueue(pendingPost);
if (!executorRunning) {
executorRunning = true;
eventBus.getExecutorService().execute(this);
}
}
}
@Override
public void run() {
try {
try {
while (true) {
PendingPost pendingPost = queue.poll(1000);
if (pendingPost == null) {
synchronized (this) {
pendingPost = queue.poll();
if (pendingPost == null) {
executorRunning = false;
return;
}
}
}
eventBus.invokeSubscriber(pendingPost);
}
} catch (InterruptedException e) {
eventBus.getLogger().log(Level.WARNING, Thread.currentThread().getName() + " was interruppted", e);
}
} finally {
executorRunning = false;
}
}
}
ASYNC
无论在哪个线程发送事件,都会先将事件加入到队列中,然后通过线程池去执行。
class AsyncPoster implements Runnable, Poster {
private final PendingPostQueue queue;
private final EventBus eventBus;
AsyncPoster(EventBus eventBus) {
this.eventBus = eventBus;
queue = new PendingPostQueue();
}
public void enqueue(Subscription subscription, Object event) {
PendingPost pendingPost = PendingPost.obtainPendingPost(subscription, event);
queue.enqueue(pendingPost);
eventBus.getExecutorService().execute(this);
}
@Override
public void run() {
PendingPost pendingPost = queue.poll();
if(pendingPost == null) {
throw new IllegalStateException("No pending post available");
}
eventBus.invokeSubscriber(pendingPost);
}
}