1、EventBus.getDefault().register(this)，getDefault()无非就是返回单例，所以直接看构造：
//subscriptionsByEventType，按事件类型订阅，key为事件类型，也就是参数名，value为有这种事件类型的集合
private final Map<Class<?>, CopyOnWriteArrayList<Subscription>> subscriptionsByEventType;
//typesBySubscriber，按订阅者类型，key为订阅者，value该订阅者的事件类型
private final Map<Object, List<Class<?>>> typesBySubscriber;
private final Map<Class<?>, Object> stickyEvents;
public EventBus() {
this(DEFAULT_BUILDER); //DEFAULT_BUILDER就是EventBusBuilder
}
EventBus(EventBusBuilder builder) {
subscriptionsByEventType = new HashMap<>();
typesBySubscriber = new HashMap<>();
stickyEvents = new ConcurrentHashMap<>();
mainThreadPoster = new HandlerPoster(this, Looper.getMainLooper(), 10); //Handler
backgroundPoster = new BackgroundPoster(this); //对应background模式，实现了runnable
asyncPoster = new AsyncPoster(this); //对应async模式
indexCount = builder.subscriberInfoIndexes != null ? builder.subscriberInfoIndexes.size() : 0;
subscriberMethodFinder = new SubscriberMethodFinder(builder.subscriberInfoIndexes,
builder.strictMethodVerification, builder.ignoreGeneratedIndex); //见名只意，找订阅者的方法
logSubscriberExceptions = builder.logSubscriberExceptions;
logNoSubscriberMessages = builder.logNoSubscriberMessages;
sendSubscriberExceptionEvent = builder.sendSubscriberExceptionEvent;
sendNoSubscriberEvent = builder.sendNoSubscriberEvent;
throwSubscriberException = builder.throwSubscriberException;
eventInheritance = builder.eventInheritance;
executorService = builder.executorService; //线程池
}
接下来看register：
public void register(Object subscriber) {
Class<?> subscriberClass = subscriber.getClass();
//寻找这个订阅者方法，通过反射获取方法遍历判断
List<SubscriberMethod> subscriberMethods = subscriberMethodFinder.findSubscriberMethods(subscriberClass);
synchronized (this) {
for (SubscriberMethod subscriberMethod : subscriberMethods) {
subscribe(subscriber, subscriberMethod); //这里是存储信息
}
}
}
看这个方法subscriberMethodFinder.findSubscriberMethods(subscriberClass)：
//返回这个订阅者的方法集合
List<SubscriberMethod> findSubscriberMethods(Class<?> subscriberClass) {
List<SubscriberMethod> subscriberMethods = METHOD_CACHE.get(subscriberClass);
if (subscriberMethods != null) { //看有没缓存，没有再往下走
return subscriberMethods;
}
if (ignoreGeneratedIndex) { //默认是false
subscriberMethods = findUsingReflection(subscriberClass);
} else {
subscriberMethods = findUsingInfo(subscriberClass); //所以走这一步
}
if (subscriberMethods.isEmpty()) { //找不到方法就抛异常
throw new EventBusException("Subscriber " + subscriberClass
+ " and its super classes have no public methods with the @Subscribe annotation");
} else {
METHOD_CACHE.put(subscriberClass, subscriberMethods); //有就加入缓存
return subscriberMethods;
}
}
下面看下findUsingInfo：
private List<SubscriberMethod> findUsingInfo(Class<?> subscriberClass) {
FindState findState = prepareFindState(); //用来存储寻找过程的信息
findState.initForSubscriber(subscriberClass); //给findState.clazz赋值
while (findState.clazz != null) {
//上一步的ignoreGeneratedIndex作用就是在这里，但默认的为null，我的理解是用户的预处理
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); //所以走这一步
}
findState.moveToSuperclass(); //寻找父类，如果是Android原生的跳出循环
}
return getMethodsAndRelease(findState);
}
findUsingReflectionInSingleClass(findState)：
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(); //获得所有方法
} 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) { 遍历
int modifiers = method.getModifiers();
if ((modifiers & Modifier.PUBLIC) != 0 && (modifiers & MODIFIERS_IGNORE) == 0) {
Class<?>[] parameterTypes = method.getParameterTypes(); //拿到方法的参数
if (parameterTypes.length == 1) { //是否是一个参数
Subscribe subscribeAnnotation = method.getAnnotation(Subscribe.class); //有没注解
if (subscribeAnnotation != null) {
Class<?> eventType = parameterTypes[0];
if (findState.checkAdd(method, eventType)) {
ThreadMode threadMode = subscribeAnnotation.threadMode();
//保存到FindState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");
}
}
}
经过上面的方法查找，满足条件的方法信息会保存到FindState，那么回到上面的findUsingInfo最后的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;
}
上面就很简单，返回的找到的符合的方法集合，到这里寻找订阅者方法走完，回到register的subscribe：
//参数一是订阅者，二是订阅者的方法
private void subscribe(Object subscriber, SubscriberMethod subscriberMethod) {
Class<?> eventType = subscriberMethod.eventType; //eventType是方法参数的类型
Subscription newSubscription = new Subscription(subscriber, subscriberMethod);
CopyOnWriteArrayList<Subscription> subscriptions = subscriptionsByEventType.get(eventType);
if (subscriptions == null) { //看有没这种参数类型的集合
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++) { //优先级比较
if (i == size || subscriberMethod.priority > subscriptions.get(i).subscriberMethod.priority) {
subscriptions.add(i, newSubscription);
break;
}
}
//下面同理，保存订阅者的方法信息
List<Class<?>> subscribedEvents = typesBySubscriber.get(subscriber);
if (subscribedEvents == null) {
subscribedEvents = new ArrayList<>();
typesBySubscriber.put(subscriber, subscribedEvents);
}
subscribedEvents.add(eventType);
//粘性事件
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);
}
}
}
2、注册事件流程就到这里，总结一下，注册流程会通过反射去找到订阅者对应的接收事件的方法，然后做相应的保存，接下来看post流程：
/** Posts the given event to the event bus. */
public void post(Object event) {
//currentPostingThreadState是ThreadLocal，线程互不干扰，拿到当前线程的PostingThreadState
PostingThreadState postingState = currentPostingThreadState.get();
List<Object> eventQueue = postingState.eventQueue; //当前线程的事件队列
eventQueue.add(event);
if (!postingState.isPosting) { //是不是在发送
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); //最后走这一步
}
} finally {
postingState.isPosting = false;
postingState.isMainThread = false;
}
}
}
往下看 postSingleEvent：
private void postSingleEvent(Object event, PostingThreadState postingState) throws Error {
Class<?> eventClass = event.getClass();
boolean subscriptionFound = false;
if (eventInheritance) { //Inheritance继承的意思
//寻找事件的父类与接口，比如我发送TextView，那么如果是View也会接收到
List<Class<?>> eventTypes = lookupAllEventTypes(eventClass);
int countTypes = eventTypes.size();
for (int h = 0; h < countTypes; h++) { //遍历发送
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));
}
}
}
接着看postSingleEventForEventType：
private boolean postSingleEventForEventType(Object event, PostingThreadState postingState, Class<?> eventClass) {
CopyOnWriteArrayList<Subscription> subscriptions;
synchronized (this) {
subscriptions = subscriptionsByEventType.get(eventClass); //注册的时候添加过
}
if (subscriptions != null && !subscriptions.isEmpty()) {
for (Subscription subscription : subscriptions) {
postingState.event = event;
postingState.subscription = subscription;
boolean aborted = false;
try { //赋值一些信息，开始发送
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;
}
再往下postToSubscription，分为四种模式：
private void postToSubscription(Subscription subscription, Object event, boolean isMainThread) {
switch (subscription.subscriberMethod.threadMode) {
case POSTING:
invokeSubscriber(subscription, event); //最终调用method invoke来执行订阅者的方法
break;
case MAIN:
if (isMainThread) {
invokeSubscriber(subscription, event); //主线程直接执行
} else {
mainThreadPoster.enqueue(subscription, event); //handler到主线程执行
}
break;
case BACKGROUND:
if (isMainThread) {
backgroundPoster.enqueue(subscription, event); //主线程就交给线程池
} else {
invokeSubscriber(subscription, event); //子线程直接运行
}
break;
case ASYNC:
asyncPoster.enqueue(subscription, event); //无论怎样都交给线程池
break;
default:
throw new IllegalStateException("Unknown thread mode: " + subscription.subscriberMethod.threadMode);
}
}
总之，事件的传递最终都是通过反射invoke调用对应订阅者对应的方法。从头到尾总结下，注册时，会通过反射找到这个订阅者所有符合条件的方法并存储起来，这里条件指的是注解和参数，然后发送消息会遍历存储的订阅者的信息，符合条件的通过反射直接调用对应的方法。
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