EventBus链接地址
一，首先就是看到EventBus这个类。
1，获取EventBus，通过单例模式：EventBus.getDefault()，它无参的构造方法里面，调用了含有EventBusBuilder参数的构造方法，这个构造方法对数据进行初始化。因为用了单例模式，只存在一个实例对象，对于变量进行初始化一次。
/** Convenience singleton for apps using a process-wide EventBus instance. */
//单例模式
public static EventBus getDefault() {
if (defaultInstance == null) {
synchronized (EventBus.class) {
if (defaultInstance == null) {
defaultInstance = new EventBus();
}
}
}
return defaultInstance;
}
public static EventBusBuilder builder() {
return new EventBusBuilder();
}
对数据进行初始化。
EventBus(EventBusBuilder builder) {
subscriptionsByEventType = new HashMap<>();
typesBySubscriber = new HashMap<>();
stickyEvents = new ConcurrentHashMap<>();
mainThreadPoster = new HandlerPoster(this, Looper.getMainLooper(), 10);
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;
}
总的流程就是：大部分的事情都是注册的时候干完了。注册的时候需要传递一个参数，一般就是传递当前类。然后根据这个类，通过反射，找到里面所有的带{@link Subscribe}.注解的方法，这个类里面可以有多个订阅者。注册方法里面获取订阅者集合：
List<SubscriberMethod> subscriberMethods = subscriberMethodFinder.findSubscriberMethods(subscriberClass);
然后对这个集合进行处理，我们需要的是什么?是发布消息，然后订阅者获取信息，执行方法。
synchronized (this) {
for (SubscriberMethod subscriberMethod : subscriberMethods) {
subscribe(subscriber, subscriberMethod);
}
}
post(Object event) 与 subscribe(Object event)，发布信息不订阅者获取信息的参数类型必须是一致的，才可以相互匹配，
这里面存在一个Map，
private final Map<Class<?>, CopyOnWriteArrayList<Subscription>> subscriptionsByEventType;
key就是eventType(方法里面的参数的Class类)，value就是订阅者方法的集合。这样，在发布消息的时候，根据发布者方法的参数来查找订阅者集合，然后进行处理。当然，既然有注册，必然存在取消注册。
二，通过使用来看EventBus的注册。
在注册的时候，通过参数来查询到了这个类里面的所有的订阅者集合，
然后对返回的集合进行处理，我们在发布消息的时候，post(Object event),
这里面就是根据event这个事件，重新获取到拥有相同的事件的集合。这样，在发布消息的时候，可以根据event直接获取到集合，然后再进行处理。
EventBus.getDefault().register(Object subscriber);
public void register(Object subscriber) {
Class<?> subscriberClass = subscriber.getClass();
//获取这个类里面的订阅者集合
List<SubscriberMethod> subscriberMethods = subscriberMethodFinder.findSubscriberMethods(subscriberClass);
synchronized (this) {
for (SubscriberMethod subscriberMethod : subscriberMethods) {
//对获取的集合进行根据eventType进行处理。
subscribe(subscriber, subscriberMethod);
}
}
}
主要就是在subscriberMethodFinder这个类里面，获取到了订阅方法的结合类。
我们可以在onCreate里面写注册，在onDestory里面写取消。然后就可以写订阅的方法。通过这个subscriber.getClass获取到的Class类，这个Class类作为一个key值，对应了一个订阅者的集合的value。也就是说，我们可以在一个类里面写多个订阅方法。
subscriberMethodFinder:
源码是如何去获取订阅者的集合
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;
}
}
最终就会走到这样一个方法里面：通过反射类获取到方法的数组，然后for循环数组，通过查找@sunscriber的注解来找到订阅者method.getAnnotation(Subscribe.class)
private void findUsingReflectionInSingleClass(FindState findState) {
Method[] methods;
try {
// This is faster than getMethods, especially when subscribers are fat classes like Activities
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);
if (subscribeAnnotation != null) {
Class<?> eventType = parameterTypes[0];
if (findState.checkAdd(method, eventType)) {
ThreadMode threadMode = subscribeAnnotation.threadMode();
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");
}
}
}
三，取消注册
/** 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());
}
}
/** Only updates subscriptionsByEventType, not typesBySubscriber! Caller must update typesBySubscriber. */
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--;
}
}
}
}
四，发布消息
EventBus.getDefault().post(Object event)
/** Posts the given event to the event bus. */
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;
}
}
}
private void postSingleEvent(Object event, PostingThreadState postingState) throws Error {
Class<?> eventClass = event.getClass();
boolean subscriptionFound = false;
if (eventInheritance) {
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) {
Log.d(TAG, "No subscribers registered for event " + eventClass);
}
if (sendNoSubscriberEvent && eventClass != NoSubscriberEvent.class &&
eventClass != SubscriberExceptionEvent.class) {
post(new NoSubscriberEvent(this, event));
}
}
}
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;
}
