EventBus 基础
发布者通过EventBus发布事件，订阅者通过EventBus订阅事件。当发布者发布事件时，订阅该事件的订阅者的事件处理方法将被调用。这里的事件，指的是一个对象类型。只有对象类型相同时，订阅方法才会被处理，还支持订阅方法在不同的线程中被调用
首先是注册方法,获取对象的Class对象，然后去SubscriberMethodFinder类中查找，
public void register(Object subscriber) {
Class<?> subscriberClass = subscriber.getClass();
List<SubscriberMethod> subscriberMethods = this.subscriberMethodFinder.findSubscriberMethods(subscriberClass);
synchronized(this) {
Iterator var5 = subscriberMethods.iterator();
while(var5.hasNext()) {
SubscriberMethod subscriberMethod = (SubscriberMethod)var5.next();
this.subscribe(subscriber, subscriberMethod);
}
}
}
SubscriberMethodFinder findSubscriberMethods方法，首先去METHOD_CACHE缓存中查找是否对应的List集合，METHOD_CACHE是个Map<Class<?>, List<SubscriberMethod>>集合，每个Class对应的List<SubscriberMethod> 都缓存在这个集合中，由于我们是第一次调用，这个获取的肯定是个null，ignoreGeneratedIndex这个我们也没赋值过，所以是个false,因此走findUsingInfo方法
findSubscriberMethods
List<SubscriberMethod> findSubscriberMethods(Class<?> subscriberClass) {
List<SubscriberMethod> subscriberMethods = (List)METHOD_CACHE.get(subscriberClass);
if (subscriberMethods != null) {
return subscriberMethods;
} else {
if (this.ignoreGeneratedIndex) {
subscriberMethods = this.findUsingReflection(subscriberClass);
} else {
subscriberMethods = this.findUsingInfo(subscriberClass);
}
if (subscriberMethods.isEmpty()) {
throw new EventBusException("Subscriber " + subscriberClass + " and its super classes have no public methods with the @Subscribe annotation");
} else {
METHOD_CACHE.put(subscriberClass, subscriberMethods);
return subscriberMethods;
}
}
}
findUsingInfo方法
传入的是我们的对象的Class对象，首先初始化了一个FindState类，然后根据当前类对象，查找是否有@Subscribe 注解的类，并且依次遍历父Class对象，直到父类是系统为止
private List<SubscriberMethod> findUsingInfo(Class<?> subscriberClass) {
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 {
findUsingReflectionInSingleClass(findState);
}
findState.moveToSuperclass();
}
return getMethodsAndRelease(findState);
}
moveToSuperclass方法，获取父类类对象，如果是系统的则直接返回null,当然如果设置了skipSuperClasses为true,则也不会搜索父类
void moveToSuperclass() {
if (this.skipSuperClasses) {
this.clazz = null;
} else {
this.clazz = this.clazz.getSuperclass();
String clazzName = this.clazz.getName();
if (clazzName.startsWith("java.") || clazzName.startsWith("javax.") || clazzName.startsWith("android.")) {
this.clazz = null;
}
}
}
findUsingReflectionInSingleClass方法，首先获取类所有的方法，然后一一查找方法上面的注解，如果找到了Subscribe注解，则把注解的ThredMode数据和方法，参数类型等数据封装成一个SubscriberMethod对象，存在findState.subscriberMethods集合中，并且参数只能有一个，如果有多个，并且设置了strictMethodVerification为true的话，则抛出一个异常。
private void findUsingReflectionInSingleClass(FindState findState) {
Method[] methods;
try {
// This is faster than getMethods, especially when subscribers are fat classes like Activities
//获取所有方法
methods = findState.clazz.getDeclaredMethods();
} catch (Throwable th) {
// Workaround for java.lang.NoClassDefFoundError, see https://github.com/greenrobot/EventBus/issues/149
methods = findState.clazz.getMethods();
findState.skipSuperClasses = true;
}
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) {
Subscribe subscribeAnnotation = method.getAnnotation(Subscribe.class);
//找到注解为Subscribe方法
if (subscribeAnnotation != null) {
Class<?> eventType = parameterTypes[0];
if (findState.checkAdd(method, eventType)) {
ThreadMode threadMode = subscribeAnnotation.threadMode();
//把方法和参数类型相关参数封装成一个SubscriberMethod对象存在findState.subscriberMethods集合中
findState.subscriberMethods.add(new SubscriberMethod(method, eventType, threadMode,
subscribeAnnotation.priority(), subscribeAnnotation.sticky()));
}
}
} else if (strictMethodVerification && method.isAnnotationPresent(Subscribe.class)) {
String methodName = method.getDeclaringClass().getName() + "." + method.getName();
throw new EventBusException("@Subscribe method " + methodName +
"must have exactly 1 parameter but has " + parameterTypes.length);
}
} else if (strictMethodVerification && method.isAnnotationPresent(Subscribe.class)) {
String methodName = method.getDeclaringClass().getName() + "." + method.getName();
throw new EventBusException(methodName +
" is a illegal @Subscribe method: must be public, non-static, and non-abstract");
}
}
}
前面我们知道找到的注解的方法都封装在findState.subscriberMethods集合中,执行getMethodsAndRelease方法则是把findState.subscriberMethods集合中的数据返回回去，
private List<SubscriberMethod> findUsingInfo(Class<?> subscriberClass) {
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 {
findUsingReflectionInSingleClass(findState);
}
findState.moveToSuperclass();
}
return getMethodsAndRelease(findState);
}
private List<SubscriberMethod> getMethodsAndRelease(FindState findState) {
List<SubscriberMethod> subscriberMethods = new ArrayList<>(findState.subscriberMethods);
findState.recycle();
synchronized (FIND_STATE_POOL) {
for (int i = 0; i < POOL_SIZE; i++) {
if (FIND_STATE_POOL[i] == null) {
FIND_STATE_POOL[i] = findState;
break;
}
}
}
return subscriberMethods;
}
在回到findSubscriberMethods方法，获取到所有方法后，缓存到METHOD_CACHE集合中，并且将所有方法返回
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");
} else {
METHOD_CACHE.put(subscriberClass, subscriberMethods);
return subscriberMethods;
}
}
回到Event的register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);
}
}
}
后又调用了subscribe方法，传入的参数就是我们注册的对象，和注册对象里的订阅方法,把我们注册的对象和方法封装成一个Subscription对象，根据方法参数类型，从subscriptionsByEventType集合中获取是否有CopyOnWriteArrayList<Subscription>集合
如果这种事件类型还没注册个过，则重新生成一个集合，并把当前的subsriptions对象添加集合中，而Subscription对象后面又添加到Subscription对象集合当中。这个subscriptionsByEventType就存储了所有事件类型，和事件类型对应的要接收所有对象。
后面post方法的时候就是从这个集合中获取对应的执行类和方法再反射执行的
private void subscribe(Object subscriber, SubscriberMethod subscriberMethod) {
Class<?> eventType = subscriberMethod.eventType;
Subscription newSubscription = new Subscription(subscriber, subscriberMethod);
CopyOnWriteArrayList<Subscription> subscriptions = subscriptionsByEventType.get(eventType);
if (subscriptions == null) {
subscriptions = new CopyOnWriteArrayList<>();
subscriptionsByEventType.put(eventType, subscriptions);
} 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);
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);
}
}
}
小结:register传入的参数是我们订阅者对象，然后查找所有该对象类里面所有带有注解Subscribe的方法，并且该方法有且只有一个参数，订阅者才会收到事件，然后把该对象和对应的参数类型封装成Subscription对象存在subscriptionsByEventType Map集合中，该集合的key类型为参数类型。
当我准备设置strictMethodVerification变量时，通过EventBus.builder().strictMethodVerification(true)设置，但是注册还是通过EventBus.getDefault().register()。发现设置的根本无效.
查看代码得知build返回的是直接new 出来的一个EventBus，而getDefault则是全局唯一，单例的，并且里面这个值默认是个false.现在发现如果要重新设置这个值，则就得重新生成一个EventBus对象，当然，其他的属性值也是如此。为什么这么设计呢，如果不这样设计，那只要一个地方改变了这个值，则所有地方都会影响。
public EventBus build() {
return new EventBus(this);
}
public static EventBus getDefault() {
if (defaultInstance == null) {
synchronized (EventBus.class) {
if (defaultInstance == null) {
defaultInstance = new EventBus();
}
}
}
return defaultInstance;
}
看使用，post方法
public void post(Object event) {
PostingThreadState postingState = currentPostingThreadState.get();
List<Object> eventQueue = postingState.eventQueue;
eventQueue.add(event);
if (!postingState.isPosting) {
postingState.isMainThread = Looper.getMainLooper() == Looper.myLooper();
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);
}
} finally {
postingState.isPosting = false;
postingState.isMainThread = false;
}
}
}
调用了postSingleEvent方法，因为我们没有设置eventInheritance属性，则走下面postSingleEventForEventType，方法，如果设置了这个属性，则所有订阅了该事件，事件实现的接口，事件的父类以及父类实现的接口的方法都会执行。
private void postSingleEvent(Object event, PostingThreadState postingState) throws Error {
Class<?> eventClass = event.getClass();
boolean subscriptionFound = false;
if (eventInheritance) {
1 查找所有事件类型，包含事件父类已经父类实现的接口
List<Class<?>> eventTypes = lookupAllEventTypes(eventClass);
int countTypes = eventTypes.size();
for (int h = 0; h < countTypes; h++) {
Class<?> clazz = eventTypes.get(h);
2 执行订阅者的方法
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方法，从subscriptionsByEventType获取所有订阅了该事件类型的调用者，然后根据是否在主线程还是其他线程一一对其调用，调用了postToSubscription方法
private boolean postSingleEventForEventType(Object event, PostingThreadState postingState, Class<?> eventClass) {
CopyOnWriteArrayList<Subscription> subscriptions;
synchronized (this) {
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);
aborted = postingState.canceled;
} finally {
postingState.event = null;
postingState.subscription = null;
postingState.canceled = false;
}
if (aborted) {
break;
}
}
return true;
}
return false;
}
根据当前调用者的线程情况，再结合注解上面的threadMode属性判断是否在哪个线程执行，
ThreadMode.POSTING 订阅者方法将在发布事件所在的线程中被调用。这是 默认的线程模式。事件的传递是同步的，一旦发布事件，所有该模式的订阅者方法都将被调用。这种线程模式意味着最少的性能开销，因为它避免了线程的切换。因此，对于不要求是主线程并且耗时很短的简单任务推荐使用该模式。使用该模式的订阅者方法应该快速返回，以避免阻塞发布事件的线程，这可能是主线程
ThreadMode.MAIN 订阅者方法将在主线程（UI线程）中被调用。因此，可以在该模式的订阅者方法中直接更新UI界面。如果发布事件的线程是主线程，那么该模式的订阅者方法将被直接调用。使用该模式的订阅者方法必须快速返回，以避免阻塞主线程。
ThreadMode.MAIN_ORDERED 订阅者方法将在主线程（UI线程）中被调用。因此，可以在该模式的订阅者方法中直接更新UI界面。事件将先进入队列然后才发送给订阅者，所以发布事件的调用将立即返回。这使得事件的处理保持严格的串行顺序。使用该模式的订阅者方法必须快速返回，以避免阻塞主线程。
ThreadMode.BACKGROUND 订阅者方法将在后台线程中被调用。如果发布事件的线程不是主线程，那么订阅者方法将直接在该线程中被调用。如果发布事件的线程是主线程，那么将使用一个单独的后台线程，该线程将按顺序发送所有的事件。使用该模式的订阅者方法应该快速返回，以避免阻塞后台线程。
ThreadMode.ASYNC 订阅者方法将在一个单独的线程中被调用。因此，发布事件的调用将立即返回。如果订阅者方法的执行需要一些时间，例如网络访问，那么就应该使用该模式。避免触发大量的长时间运行的订阅者方法，以限制并发线程的数量。EventBus使用了一个线程池来有效地重用已经完成调用订阅者方法的线程。
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);
}
}
其中POSTING执行的方法，反射的调用其对应的方法
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);
}
}
如果当前post的代码没有在主线程中，则利用主线程的mainThreadPoster 切换到主线程中执行
register是把对象存起来，unregister就是把对象移除
/** Unregisters the given subscriber from all event classes. */
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());
}
}
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