前言
在項(xiàng)目中遇到了有關(guān)EventBus數(shù)據(jù)方面的問題脆侮，于是就參考源碼梳理一下整個(gè)數(shù)據(jù)流程，最后整理輸出雅倒。
簡(jiǎn)介
EventBus是一個(gè)基于觀察者模式的發(fā)布/訂閱事件總線绅络，解決了以往廣播在組件間通信的不安全、耗時(shí)問題狈茉，替代Intent,Handler,BroadCast在Fragment夫椭，Activity，Service氯庆，線程之間傳遞消息蹭秋。
EventBus
優(yōu)缺點(diǎn)
優(yōu)點(diǎn)->簡(jiǎn)化組件之間的通信，實(shí)現(xiàn)解耦使業(yè)務(wù)簡(jiǎn)潔堤撵，高效仁讨，可以自己設(shè)置事件處理的線程以及優(yōu)先級(jí)。
缺點(diǎn)->需要維護(hù)很多事件類实昨。
使用
-
定義事件:
public static class MessageEvent { /* Additional fields if needed */ } -
準(zhǔn)備訂閱者: 申明并注解你的訂閱方法, 指定線程模式(可選)
@Subscribe(threadMode = ThreadMode.MAIN) public void onMessageEvent(MessageEvent event) {/* Do something */};在使用的類中陪竿，注冊(cè)和解注冊(cè)訂閱者，如Activity/fragment中:
@Override public void onStart() { super.onStart(); EventBus.getDefault().register(this); } @Override public void onStop() { super.onStop(); EventBus.getDefault().unregister(this); } -
發(fā)送事件:
EventBus.getDefault().post(new MessageEvent());
內(nèi)部實(shí)現(xiàn)
1.EventBus.getDefault().register(this);
注冊(cè)給定的訂閱用戶以接收事件。訂閱者對(duì)接收事件不再感興趣后族跛，必須調(diào)用{@link #unregister（Object）}闰挡。
public void register(Object subscriber) {
//通過反射獲取訂閱者Class對(duì)象
Class<?> subscriberClass = subscriber.getClass();
//1.5
List<SubscriberMethod> subscriberMethods = subscriberMethodFinder.findSubscriberMethods(subscriberClass);
synchronized (this) {
//遍歷訂閱
for (SubscriberMethod subscriberMethod : subscriberMethods) {
//2
subscribe(subscriber, subscriberMethod);
}
}
}
通過Class對(duì)象獲取它的訂閱事件的集合
1.SubscriberMethodFinder#List<SubscriberMethod> findSubscriberMethods(Class<?> subscriberClass)
List<SubscriberMethod> findSubscriberMethods(Class<?> subscriberClass) {
//private static final Map<Class<?>, List<SubscriberMethod>> METHOD_CACHE = new ConcurrentHashMap<>();
//這個(gè)Map key為注冊(cè)事件的類(比如某個(gè)Activity)，value為承載著事件類(MessageEvent)和處理事件的方法(onMessageEvent(MessageEvent event))
//先從此處查找 不為空返回 為空 就添加到map中
List<SubscriberMethod> subscriberMethods = METHOD_CACHE.get(subscriberClass);
if (subscriberMethods != null) {
return subscriberMethods;
}
if (ignoreGeneratedIndex) {
subscriberMethods = findUsingReflection(subscriberClass);
} else {
//1.1 獲取所有訂閱者的方法列表
subscriberMethods = findUsingInfo(subscriberClass);
}
//不為空 就添加到map中
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;
}
}
1.1 SubscriberMethodFinder#List<SubscriberMethod> findUsingInfo(Class<?> subscriberClass)
private List<SubscriberMethod> findUsingInfo(Class<?> subscriberClass) {
//從FIND_STATE_POOL (private static final FindState[] FIND_STATE_POOL = new FindState[POOL_SIZE]; POOL_SIZE->4)
//中獲取FindState對(duì)象
FindState findState = prepareFindState();
findState.initForSubscriber(subscriberClass);
while (findState.clazz != null) {
findState.subscriberInfo = getSubscriberInfo(findState);
//第一次為null
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 {
//通過反射獲取訂閱者類中的所有方法
findUsingReflectionInSingleClass(findState);
}
findState.moveToSuperclass();
}
//從findState中獲取訂閱者所有方法的集合
return getMethodsAndRelease(findState);
}
2.EventBus#subscribe(Object subscriber, SubscriberMethod subscriberMethod)
private void subscribe(Object subscriber, SubscriberMethod subscriberMethod) {
//獲取事件類型的Class對(duì)象
Class<?> eventType = subscriberMethod.eventType;
//將信息封裝到對(duì)象中
Subscription newSubscription = new Subscription(subscriber, subscriberMethod);
//根據(jù)事件類型查找對(duì)應(yīng)的CopyOnWriteArrayList
CopyOnWriteArrayList<Subscription> subscriptions = subscriptionsByEventType.get(eventType);
if (subscriptions == null) {
subscriptions = new CopyOnWriteArrayList<>();
subscriptionsByEventType.put(eventType, subscriptions);
} else {
//只能注冊(cè)一次
if (subscriptions.contains(newSubscription)) {
throw new EventBusException("Subscriber " + subscriber.getClass() + " already registered to event "
+ eventType);
}
}
//根據(jù)優(yōu)先級(jí)將新構(gòu)建的subscription(subscriber, subscriberMethod)添加到CopyOnWriteArrayList中
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);
//如果是sticky事件 調(diào)用checkPostStickyEventToSubscription方法發(fā)送粘性事件
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);
}
}
}
注冊(cè)部分主要通過通過訂閱者的Class對(duì)象獲取其中的訂閱方法礁哄，將方法和訂閱者綁定长酗，之后又處理了粘性事件。
2. EventBus.getDefault().post(new MessageEvent());
public void post(Object event) {
//currentPostingThreadState(是ThreadLocal)獲取PostingThreadState
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 {
//如果事件隊(duì)列中還有事件 就一直發(fā)送
while (!eventQueue.isEmpty()) {
//3
postSingleEvent(eventQueue.remove(0), postingState);
}
} finally {
postingState.isPosting = false;
postingState.isMainThread = false;
}
}
}
final static class PostingThreadState {
final List<Object> eventQueue = new ArrayList<>(); // 線程的事件隊(duì)列
boolean isPosting; //是否正在發(fā)送
boolean isMainThread; //是否在主線程中發(fā)送
Subscription subscription; //關(guān)于事件的封裝
Object event; //事件對(duì)象
boolean canceled; //是否被取消發(fā)送
}
3.EventBus#postSingleEvent(Object event, PostingThreadState postingState)
private void postSingleEvent(Object event, PostingThreadState postingState) throws Error {
Class<?> eventClass = event.getClass();
boolean subscriptionFound = false;
if (eventInheritance) {
//查找所有Class對(duì)象桐绒，包括超類和接口
List<Class<?>> eventTypes = lookupAllEventTypes(eventClass);
int countTypes = eventTypes.size();
for (int h = 0; h < countTypes; h++) {
Class<?> clazz = eventTypes.get(h);
//調(diào)用postSingleEventForEventType方法發(fā)送事件
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));
}
}
}
private boolean postSingleEventForEventType(Object event, PostingThreadState postingState, Class<?> eventClass) {
CopyOnWriteArrayList<Subscription> subscriptions;
synchronized (this) {
//獲取所有訂閱者
subscriptions = subscriptionsByEventType.get(eventClass);
}
if (subscriptions != null && !subscriptions.isEmpty()) {
for (Subscription subscription : subscriptions) {
postingState.event = event;
postingState.subscription = subscription;
boolean aborted = false;
try {
//發(fā)送事件
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;
}
//粘性事件會(huì)直接調(diào)用這個(gè)
//根據(jù)注解上的線程模式在不用的線程調(diào)用
private void postToSubscription(Subscription subscription, Object event, boolean isMainThread) {
switch (subscription.subscriberMethod.threadMode) {
case POSTING://直接反射調(diào)用方法 不切換線程
invokeSubscriber(subscription, event);
break;
case MAIN://在主線程直接反射調(diào)用
if (isMainThread) {
invokeSubscriber(subscription, event);
} else { //否則加入到列隊(duì)中到主線程調(diào)用
mainThreadPoster.enqueue(subscription, event);
}
break;
case MAIN_ORDERED://與MAIN類似
if (mainThreadPoster != null) {
mainThreadPoster.enqueue(subscription, event);
} else {
invokeSubscriber(subscription, event);
}
break;
case BACKGROUND:
if (isMainThread) {//在主線程就加入后臺(tái)隊(duì)列執(zhí)行
backgroundPoster.enqueue(subscription, event);
} else {//直接反射調(diào)用
invokeSubscriber(subscription, event);
}
break;
case ASYNC://直接在子線程調(diào)用
asyncPoster.enqueue(subscription, event);
break;
default:
throw new IllegalStateException("Unknown thread mode: " + subscription.subscriberMethod.threadMode);
}
}
post方法主要將事件加入集合并且集合還有數(shù)據(jù)就一直發(fā)送夺脾，然后獲取所有訂閱該事件類的訂閱者，判斷他們需要運(yùn)行的線程來(lái)決定在哪個(gè)線程運(yùn)行茉继。
3.EventBus.getDefault().postSticky(new MessageEvent());
//加入到粘性事件列表中供之后判斷
public void postSticky(Object event) {
synchronized (stickyEvents) {
stickyEvents.put(event.getClass(), event);
}
//發(fā)送事件
post(event);
}
將數(shù)據(jù)加入到粘性事件列表在registe方法中判斷是否post事件
4.EventBus.getDefault().unregister(this);
public synchronized void unregister(Object subscriber) {
//獲取訂閱者的所有訂閱事件
List<Class<?>> subscribedTypes = typesBySubscriber.get(subscriber);
if (subscribedTypes != null) {
for (Class<?> eventType : subscribedTypes) {
//將訂閱者的訂閱事件移除
unsubscribeByEventType(subscriber, eventType);
}
//將訂閱者移除
typesBySubscriber.remove(subscriber);
} else {
logger.log(Level.WARNING, "Subscriber to unregister was not registered before: " + subscriber.getClass());
}
}
總結(jié)
到這里EventBus源碼流程就結(jié)束了咧叭，它的源碼相較于其他來(lái)說還是比較簡(jiǎn)單的，如果文中有不足之處望指出烁竭。
