EventBus 是人們在日常開發(fā)中經(jīng)常會(huì)用到的開源庫,即使是不直接用的人,也多少借鑒過事件總線的用法。而且EventBus的代碼其實(shí)是非常簡單的,可以試著閱讀一下。
源碼閱讀系列不采用對(duì)功能進(jìn)行歸類的方法進(jìn)行閱讀,而是采用一個(gè)剛開始閱讀源碼的視角,從我們平時(shí)的API調(diào)用,一步步的去理解設(shè)計(jì)意圖和實(shí)現(xiàn)原理。
從這里開始
從這里開始吧,我們最常用的地方就是給一個(gè)函數(shù)添加上注解,我們先拋開apt生成的table,只看這個(gè)運(yùn)行時(shí)版本的訂閱設(shè)定。
// eventbus/Subscribe@Documented@Retention(RetentionPolicy.RUNTIME)@Target({ElementType.METHOD})public @interface Subscribe { ThreadMode threadMode() default ThreadMode.POSTING; /** * If true, delivers the most recent sticky event (posted with * {@link EventBus#postSticky(Object)}) to this subscriber (if event available). */ boolean sticky() default false; /** Subscriber priority to influence the order of event delivery. * Within the same delivery thread ({@link ThreadMode}), higher priority subscribers will receive events before * others with a lower priority. The default priority is 0. Note: the priority does *NOT* affect the order of * delivery among subscribers with different {@link ThreadMode}s! */ int priority() default 0; }
這個(gè)設(shè)定還是非常簡單的,而且都是我們熟悉的東西,線程類型(默認(rèn)的是拋出線程),是否是粘性事件,時(shí)間的優(yōu)先級(jí)。經(jīng)過這個(gè)類的出現(xiàn),我們就可以在類里面寫我們經(jīng)常寫的某個(gè)函數(shù)是訂閱函數(shù)了。
@Subscribe (...)public void getMessage(Event event) { ... }
下面的問題是我們改怎么讓EventBus找到這些方法呢?通過apt的版本我們知道這里面肯定有一個(gè)map或者是table的東西記錄了Object和Method之間的訂閱關(guān)系,而且還是一對(duì)多的。這個(gè)地方就是從每個(gè)我們進(jìn)行register的地方進(jìn)行的。
register & unregister
// eventbus/EventBus /** * Registers the given subscriber to receive events. Subscribers must call {@link #unregister(Object)} once they * are no longer interested in receiving events. * <p/> * Subscribers have event handling methods that must be annotated by {@link Subscribe}. * The {@link Subscribe} annotation also allows configuration like {@link * ThreadMode} and priority. */ public void register(Object subscriber) { Class<?> subscriberClass = subscriber.getClass(); List<SubscriberMethod> subscriberMethods = subscriberMethodFinder.findSubscriberMethods(subscriberClass); synchronized (this) { for (SubscriberMethod subscriberMethod : subscriberMethods) { subscribe(subscriber, subscriberMethod); } } }
我們在Activity/Fragment中都有可能會(huì)調(diào)用這個(gè)方法,如果是Fragment里面我們還會(huì)在onDestoryView()
中進(jìn)行unregister(...)
。在這段函數(shù)里我們發(fā)現(xiàn)使用反射從這個(gè)Class中找到了所有的訂閱者函數(shù)了,然后對(duì)每個(gè)訂閱者函數(shù)進(jìn)行注冊。
這里我們看看我們的SubribeMethod被包裝成了什么樣子:
/** Used internally by EventBus and generated subscriber indexes. */public class SubscriberMethod { final Method method; final ThreadMode threadMode; final Class<?> eventType; final int priority; final boolean sticky; /** Used for efficient comparison */ String methodString; public SubscriberMethod(Method method, Class<?> eventType, ThreadMode threadMode, int priority, boolean sticky) { this.method = method; this.threadMode = threadMode; this.eventType = eventType; this.priority = priority; this.sticky = sticky; } @Override public boolean equals(Object other) { if (other == this) { return true; } else if (other instanceof SubscriberMethod) { checkMethodString(); SubscriberMethod otherSubscriberMethod = (SubscriberMethod)other; otherSubscriberMethod.checkMethodString(); // Don't use method.equals because of http://code.google.com/p/android/issues/detail?id=7811#c6 return methodString.equals(otherSubscriberMethod.methodString); } else { return false; } } private synchronized void checkMethodString() { if (methodString == null) { // Method.toString has more overhead, just take relevant parts of the method StringBuilder builder = new StringBuilder(64); builder.append(method.getDeclaringClass().getName()); builder.append('#').append(method.getName()); builder.append('(').append(eventType.getName()); methodString = builder.toString(); } } @Override public int hashCode() { return method.hashCode(); } }
SubscribeMethod 攜帶了Method函數(shù)原型,還有就是我們在注解類里面提供的所有信息。還有一個(gè)Class<?>類型的EventType是指我們的事件類所對(duì)應(yīng)的Class,其余的方法都是為了比較和判斷是否相等來做的,equal/checkMethodString都是各種的拼字串來進(jìn)行存儲(chǔ)和判斷。
下面我們來看register里面調(diào)用的這段subscribe,這段非常的重要涉及了EventBus運(yùn)行時(shí)處理的絕大多數(shù)部分,還有就是粘性事件的分發(fā)。這段使用了大量的JDK的反射包的API,本身注釋也提醒我們了這段代碼需要加鎖,畢竟里面這一堆并發(fā)容器。所以我們最好先明確這段里面用的并發(fā)容器到底都是什么,這段代碼才好繼續(xù)看的下去。
private final Map<Class<?>, CopyOnWriteArrayList<Subscription>> subscriptionsByEventType; private final Map<Object, List<Class<?>>> typesBySubscriber; private final Map<Class<?>, Object> stickyEvents;
主要的有這幾個(gè):
第一個(gè)Map存儲(chǔ)的Key是Class類型,Value是一個(gè)并發(fā)的ArrayList里面存的是對(duì)訂閱者和訂閱函數(shù)的一種綁定類
Subscription
從名字上也能看出Key是Event的Class對(duì)象。第二個(gè)存儲(chǔ)的是訂閱者(Activity什么的?。┖虴vent類型的List。
第三個(gè)Map存儲(chǔ)的是粘性事件,Key是Event類型,Value是真實(shí)存在的StickyEvent對(duì)象。
知道這三個(gè)都是什么之后,這段代碼就好看了。我們來看前一部分。
// Must be called in synchronized block private void subscribe(Object subscriber, SubscriberMethod subscriberMethod) { Class<?> eventType = subscriberMethod.eventType; Subscription newSubscription = new Subscription(subscriber, subscriberMethod); // Map<Class<?>, CopyOnWriteArrayList<Subscription>> 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);
這段寫的雖然有點(diǎn)亂套,但實(shí)際上寫的挺簡單的,而且一堆堆的O(n)遍歷,性能也就那樣(?)。
首先這里面出現(xiàn)了Subscription:
final class Subscription { final Object subscriber; final SubscriberMethod subscriberMethod; /** * Becomes false as soon as {@link EventBus#unregister(Object)} is called, which is checked by queued event delivery * {@link EventBus#invokeSubscriber(PendingPost)} to prevent race conditions. */ volatile boolean active; Subscription(Object subscriber, SubscriberMethod subscriberMethod) { this.subscriber = subscriber; this.subscriberMethod = subscriberMethod; active = true; } @Override public boolean equals(Object other) { if (other instanceof Subscription) { Subscription otherSubscription = (Subscription) other; return subscriber == otherSubscription.subscriber && subscriberMethod.equals(otherSubscription.subscriberMethod); } else { return false; } } @Override public int hashCode() { return subscriber.hashCode() + subscriberMethod.methodString.hashCode(); } }
我們發(fā)現(xiàn)了這是訂閱者和訂閱方法類的一個(gè)契約關(guān)系類。
所以說上面subscribe函數(shù)主要做了,
創(chuàng)建了訂閱者和方法類的綁定,然后存進(jìn)了
subscriptionsByEventType
中對(duì)每個(gè)類型重新排列了一次優(yōu)先級(jí)
對(duì)
typesBySubscriber
添加了對(duì)應(yīng)的類型
然后我們可以看一下這個(gè)函數(shù)的下一半,我們會(huì)驚奇地發(fā)現(xiàn),StickyEvent的發(fā)送時(shí)機(jī)居然是在register的時(shí)候:
... 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); } }
這時(shí)候輪了一遍所有的粘性事件。isAssignableFrom類似于使用在Class之間的instance of
就是判斷兩個(gè)類是否有相同的接口關(guān)系,也就是說有繼承和實(shí)現(xiàn)關(guān)系的事件類,都會(huì)被判斷處理。
private void checkPostStickyEventToSubscription(Subscription newSubscription, Object stickyEvent) { if (stickyEvent != null) { // If the subscriber is trying to abort the event, it will fail (event is not tracked in posting state) // --> Strange corner case, which we don't take care of here. postToSubscription(newSubscription, stickyEvent, Looper.getMainLooper() == Looper.myLooper()); } }
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); } }
之后就是針對(duì)各種的ThreadMode進(jìn)行了處理,同一線程的直接依賴Java的反射invoke執(zhí)行了,各種不可以的情況,比如說發(fā)到主線程但還沒在主線程的時(shí)候,都是用隊(duì)列進(jìn)行發(fā)送到對(duì)應(yīng)線程。
接下來我們看看這里面在各線程之間的發(fā)送是怎么實(shí)現(xiàn)的。
消息轉(zhuǎn)換線程
我們發(fā)現(xiàn)在Subscription和event入隊(duì)的時(shí)候我們把他們封裝成了一個(gè)PendingPost類:
// HandlePoster 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"); } } } }
然后才進(jìn)行的入隊(duì)和發(fā)送,這個(gè)PendingPost就是一個(gè)帶有回收池的掩飾傳送類:
final class PendingPost { private final static List<PendingPost> pendingPostPool = new ArrayList<PendingPost>(); Object event; Subscription subscription; PendingPost next; private PendingPost(Object event, Subscription subscription) { this.event = event; this.subscription = subscription; } static PendingPost obtainPendingPost(Subscription subscription, Object event) { synchronized (pendingPostPool) { int size = pendingPostPool.size(); if (size > 0) { PendingPost pendingPost = pendingPostPool.remove(size - 1); pendingPost.event = event; pendingPost.subscription = subscription; pendingPost.next = null; return pendingPost; } } return new PendingPost(event, subscription); } static void releasePendingPost(PendingPost pendingPost) { pendingPost.event = null; pendingPost.subscription = null; pendingPost.next = null; synchronized (pendingPostPool) { // Don't let the pool grow indefinitely if (pendingPostPool.size() < 10000) { pendingPostPool.add(pendingPost); } } } }
這里的設(shè)計(jì)其實(shí)挺不錯(cuò)的,一個(gè)靜態(tài)的回收池,初始化靠一個(gè)靜態(tài)方法,優(yōu)先使用被回收的對(duì)象,實(shí)現(xiàn)和Message
其實(shí)很像。另一個(gè)release方法就是把用完的對(duì)象回收起來。
PendingPostQueue
就是一個(gè)PendingPost的隊(duì)列,里面的操作基本上就是入隊(duì)出隊(duì)之類的,有點(diǎn)特殊的是入隊(duì)和出隊(duì)都有一把鎖。
接著這個(gè)隊(duì)列被用在了好幾個(gè)Poster類中,實(shí)現(xiàn)了向各個(gè)線程的消息轉(zhuǎn)換,首先我們來看向主線程發(fā)送數(shù)據(jù)的:
HandlePoster
final class HandlerPoster extends Handler { private final PendingPostQueue queue; private final int maxMillisInsideHandleMessage; private final EventBus eventBus; private boolean handlerActive; HandlerPoster(EventBus eventBus, Looper looper, int maxMillisInsideHandleMessage) { super(looper); this.eventBus = eventBus; this.maxMillisInsideHandleMessage = maxMillisInsideHandleMessage; queue = new PendingPostQueue(); } 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) { // Check again, this time in synchronized 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; } } }
HandlePoster 繼承自 Handler 再加上初始化的時(shí)候傳進(jìn)去的是Looper.getMainThread();所以能向主線程發(fā)送消息。每次入隊(duì)之后都會(huì)發(fā)送一條空消息去通知handleMessage函數(shù)處理隊(duì)列數(shù)據(jù),使用handlerActive作為控制標(biāo)記位。handleMessage是個(gè)死循環(huán)兩段的if判斷用來處理多線程的情況,invokeSubscriber的方式和之前類似。之后就是有一個(gè)閥值,當(dāng)時(shí)間超過10ms的時(shí)候就會(huì)發(fā)一個(gè)消息重入,并且退出這次循環(huán),這是防止時(shí)間太長阻塞主線程。
BackgroundPoster
final class BackgroundPoster implements Runnable { 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) { // Check again, this time in synchronized pendingPost = queue.poll(); if (pendingPost == null) { executorRunning = false; return; } } } eventBus.invokeSubscriber(pendingPost); } } catch (InterruptedException e) { Log.w("Event", Thread.currentThread().getName() + " was interruppted", e); } } finally { executorRunning = false; } } }
BackgroundPoster
自身是一個(gè)Runnable ,入隊(duì)之后就調(diào)用EventBus攜帶的一個(gè)線程池進(jìn)行運(yùn)行,同樣也是一個(gè)死循環(huán),用了一個(gè)生產(chǎn)者 vs 消費(fèi)者模式
進(jìn)行了有限等待,這1000ms內(nèi)入隊(duì)的消息都會(huì)被彈出處理。
synchronized PendingPost poll(int maxMillisToWait) throws InterruptedException { if (head == null) { wait(maxMillisToWait); } return poll(); }
PendingPostQueue的poll(int)方法對(duì)隊(duì)列為空的情況進(jìn)行了等待,喚醒則出現(xiàn)在enqueue:
synchronized void enqueue(PendingPost pendingPost) { if (pendingPost == null) { throw new NullPointerException("null cannot be enqueued"); } if (tail != null) { tail.next = pendingPost; tail = pendingPost; } else if (head == null) { head = tail = pendingPost; } else { throw new IllegalStateException("Head present, but no tail"); } notifyAll(); // 在這進(jìn)行了喚醒 }
AsyncPoster
如果說Background尚且能保證在同一個(gè)線程內(nèi)完成,AsyncPoster就完全進(jìn)行了異步操作。
class AsyncPoster implements Runnable { 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); } }
這里面基本上什么都不控制,直接就來一個(gè)運(yùn)行一次,也不會(huì)有什么問題。。。
到這為止我們不但知道了方法是怎么注冊和綁定的,我們甚至還知道了粘性事件是怎么發(fā)送的了,接著我們來看方法查找和普通事件的發(fā)送是怎么進(jìn)行的。
方法查找
// package org.greenrobot.eventbus.meta;/** Base class for generated index classes created by annotation processing. */public interface SubscriberInfo { // 獲取訂閱的類 Class<?> getSubscriberClass(); // 所有的method SubscriberMethod[] getSubscriberMethods(); // 獲取父類的info SubscriberInfo getSuperSubscriberInfo(); // 是否檢查父類 boolean shouldCheckSuperclass(); }
SubscriberInfo
描述了能通過注解類生成的Index的方法(具體功能我加了主食)。
/** * Interface for generated indexes. */public interface SubscriberInfoIndex { SubscriberInfo getSubscriberInfo(Class<?> subscriberClass); }
這個(gè)接口是查找info的。
另外可以說這其中的SubscriberMethodInfo
存儲(chǔ)著SubscriberMethod
所需的元信息:
public class SubscriberMethodInfo { final String methodName; final ThreadMode threadMode; final Class<?> eventType; final int priority; final boolean sticky; ...
AbstractSubscriberInfo
是一個(gè)抽象類,主要負(fù)責(zé)從Info創(chuàng)建出Method,又是一個(gè)反射:
protected SubscriberMethod createSubscriberMethod(String methodName, Class<?> eventType, ThreadMode threadMode, int priority, boolean sticky) { try { Method method = subscriberClass.getDeclaredMethod(methodName, eventType); return new SubscriberMethod(method, eventType, threadMode, priority, sticky); } catch (NoSuchMethodException e) { throw new EventBusException("Could not find subscriber method in " + subscriberClass + ". Maybe a missing ProGuard rule?", e); } }
另外還有一個(gè)SimpleSubscriberInfo作為他的子類。
接下來的SubscriberMethodFinder
也非常重要運(yùn)行時(shí)的方法查找都來自這里:
剛才我們在EventBus.register(...)
中調(diào)用了這個(gè)函數(shù):
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; } }
其中的METHOD_CACHE是對(duì)每個(gè)類方法進(jìn)行緩存,防止多次查找,畢竟運(yùn)行時(shí)查找還是個(gè)復(fù)雜的操作,根據(jù)是否忽略生成Index。
private List<SubscriberMethod> findUsingReflection(Class<?> subscriberClass) { FindState findState = prepareFindState(); findState.initForSubscriber(subscriberClass); while (findState.clazz != null) { findUsingReflectionInSingleClass(findState); findState.moveToSuperclass(); } return getMethodsAndRelease(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(); } 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"); } } }
findUsingReflectionInSingleClass對(duì)反射類進(jìn)行了處理,這里面通過掩模運(yùn)算檢查了訪問權(quán)限, 檢查了參數(shù)個(gè)數(shù)。
boolean checkAdd(Method method, Class<?> eventType) { // 2 level check: 1st level with event type only (fast), 2nd level with complete signature when required. // Usually a subscriber doesn't have methods listening to the same event type. Object existing = anyMethodByEventType.put(eventType, method); if (existing == null) { return true; } else { if (existing instanceof Method) { if (!checkAddWithMethodSignature((Method) existing, eventType)) { // Paranoia check throw new IllegalStateException(); } // Put any non-Method object to "consume" the existing Method anyMethodByEventType.put(eventType, this); } return checkAddWithMethodSignature(method, eventType); } }
其中的checkAdd檢查了類型和方法簽名,每次輪轉(zhuǎn)完成之后都會(huì)進(jìn)行一次findState.moveToSuperclass();對(duì)父類進(jìn)行處理。
使用索引
因?yàn)榉瓷渌褂玫倪\(yùn)行時(shí)查找速度緩慢,所以我們也經(jīng)常會(huì)通過apt使用已經(jīng)創(chuàng)建好的Index。
剛才另一個(gè)分支的findUsingInfo
就是使用已有的Index:
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); }
這段非常簡單,幾乎就是剛才的驗(yàn)證而已,如果沒拿到數(shù)據(jù)的話,還會(huì)進(jìn)行正常的反射查找。
// EventBusAnnotationProcessor 負(fù)責(zé)生成注解路由表 private void createInfoIndexFile(String index) { BufferedWriter writer = null; try { JavaFileObject sourceFile = processingEnv.getFiler().createSourceFile(index); int period = index.lastIndexOf('.'); String myPackage = period > 0 ? index.substring(0, period) : null; String clazz = index.substring(period + 1); writer = new BufferedWriter(sourceFile.openWriter()); if (myPackage != null) { writer.write("package " + myPackage + ";\n\n"); } writer.write("import org.greenrobot.eventbus.meta.SimpleSubscriberInfo;\n"); writer.write("import org.greenrobot.eventbus.meta.SubscriberMethodInfo;\n"); writer.write("import org.greenrobot.eventbus.meta.SubscriberInfo;\n"); writer.write("import org.greenrobot.eventbus.meta.SubscriberInfoIndex;\n\n"); writer.write("import org.greenrobot.eventbus.ThreadMode;\n\n"); writer.write("import java.util.HashMap;\n"); writer.write("import java.util.Map;\n\n"); writer.write("/** This class is generated by EventBus, do not edit. */\n"); writer.write("public class " + clazz + " implements SubscriberInfoIndex {\n"); writer.write(" private static final Map<Class<?>, SubscriberInfo> SUBSCRIBER_INDEX;\n\n"); writer.write(" static {\n"); writer.write(" SUBSCRIBER_INDEX = new HashMap<Class<?>, SubscriberInfo>();\n\n"); writeIndexLines(writer, myPackage); writer.write(" }\n\n"); writer.write(" private static void putIndex(SubscriberInfo info) {\n"); writer.write(" SUBSCRIBER_INDEX.put(info.getSubscriberClass(), info);\n"); writer.write(" }\n\n"); writer.write(" @Override\n"); writer.write(" public SubscriberInfo getSubscriberInfo(Class<?> subscriberClass) {\n"); writer.write(" SubscriberInfo info = SUBSCRIBER_INDEX.get(subscriberClass);\n"); writer.write(" if (info != null) {\n"); writer.write(" return info;\n"); writer.write(" } else {\n"); writer.write(" return null;\n"); writer.write(" }\n"); writer.write(" }\n"); writer.write("}\n"); } catch (IOException e) { throw new RuntimeException("Could not write source for " + index, e); } finally { if (writer != null) { try { writer.close(); } catch (IOException e) { //Silent } } } } private void writeIndexLines(BufferedWriter writer, String myPackage) throws IOException { for (TypeElement subscriberTypeElement : methodsByClass.keySet()) { if (classesToSkip.contains(subscriberTypeElement)) { continue; } String subscriberClass = getClassString(subscriberTypeElement, myPackage); if (isVisible(myPackage, subscriberTypeElement)) { writeLine(writer, 2, "putIndex(new SimpleSubscriberInfo(" + subscriberClass + ".class,", "true,", "new SubscriberMethodInfo[] {"); List<ExecutableElement> methods = methodsByClass.get(subscriberTypeElement); writeCreateSubscriberMethods(writer, methods, "new SubscriberMethodInfo", myPackage); writer.write(" }));\n\n"); } else { writer.write(" // Subscriber not visible to index: " + subscriberClass + "\n"); } } }
有了這兩個(gè)方法之后我們就知道,平常的index就是通過這種方式拼接出來的。
Post消息
/** 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; } } }
PostingThreadState是一個(gè)存儲(chǔ)在ThreadLocal中的對(duì)象,包含有以下各種內(nèi)容,線程信息,是否是主線程,是否取消,還有一個(gè)相應(yīng)的事件隊(duì)列。
private void postSingleEvent(Object event, PostingThreadState postingState) throws Error { Class<?> eventClass = event.getClass(); boolean subscriptionFound = false; if (eventInheritance) { /** Looks up all Class objects including super classes and interfaces. Should also work for interfaces. */ List<Class<?>> eventTypes = lookupAllEventTypes(eventClass); int countTypes = eventTypes.size(); // 對(duì)所有的訂閱函數(shù),都調(diào)用發(fā)送數(shù)據(jù) for (int h = 0; h < countTypes; h++) { // 所有的訂閱類 Class<?> clazz = eventTypes.get(h); subscriptionFound |= postSingleEventForEventType(event, postingState, clazz); } } else { // 只發(fā)送一次 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) { // 無訂閱者的處理 post(new NoSubscriberEvent(this, event)); } } }
之后:
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; }
之后對(duì)所有的訂閱類的所有訂閱者都發(fā)送一次數(shù)據(jù),發(fā)送數(shù)據(jù)方法和上文相同。
發(fā)送粘性數(shù)據(jù)就是拿鎖然后保存到隊(duì)列中去,這樣就可以在重新發(fā)送:
public void postSticky(Object event) { synchronized (stickyEvents) { stickyEvents.put(event.getClass(), event); } // Should be posted after it is putted, in case the subscriber wants to remove immediately post(event); }
因?yàn)槲覀儫o法確定什么時(shí)候粘性事件應(yīng)該停止繼續(xù)傳播,這取決于我們應(yīng)用的需要,所以我們應(yīng)當(dāng)手動(dòng)remove掉Sticky Event :
// 系統(tǒng)提供了如下方法 public <T> T removeStickyEvent(Class<T> eventType) { synchronized (stickyEvents) { return eventType.cast(stickyEvents.remove(eventType)); } } public boolean removeStickyEvent(Object event) { synchronized (stickyEvents) { Class<?> eventType = event.getClass(); Object existingEvent = stickyEvents.get(eventType); if (event.equals(existingEvent)) { stickyEvents.remove(eventType); return true; } else { return false; } } } public void removeAllStickyEvents() { synchronized (stickyEvents) { stickyEvents.clear(); } }