EventBus-3.1.1源碼閱讀

1. 注冊及查找事件

1.1 EventBus初始化

getDefault：通過單例模式獲取實例愈污，同時里面采用Builder模式構造部分初始化參數(shù)张遭，方便定制部分配置信息

//Builder模式,在EventBusBuilder里面完成一些默認的初始化操作
private static final EventBusBuilder DEFAULT_BUILDER = new EventBusBuilder();

public static EventBus getDefault() {
   //通過DCL單例模式創(chuàng)建EventBus實例
}

public EventBus() {
    this(DEFAULT_BUILDER);
}

EventBus(EventBusBuilder builder) {
    //通過EventBusBuilder完成的初始化構造
}

1.2 EventBus注冊

public void register(Object subscriber) {
    //根據(jù)訂閱者的類名信息查詢訂閱方法
    Class<?> subscriberClass = subscriber.getClass();
    List<SubscriberMethod> subscriberMethods = subscriberMethodFinder.findSubscriberMethods(subscriberClass);
    synchronized (this) {
        //遍歷并注冊這些訂閱方法
        for (SubscriberMethod subscriberMethod : subscriberMethods) {
            subscribe(subscriber, subscriberMethod);
        }
    }
}

SubscriberMethod：封裝了訂閱方法的基本類型信息粥谬，即@Subscribe中所注解的內容

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;
    }

1.3 查詢訂閱者所有的訂閱方法

findSubscriberMethods：查詢訂閱者所有的訂閱方法,三種查詢方式：緩存进胯，通過注解器索引，反射

//METHOD_CACHE緩存了訂閱及其所有訂閱方法
private static final Map<Class<?>, List<SubscriberMethod>> METHOD_CACHE = new ConcurrentHashMap<>();

List<SubscriberMethod> findSubscriberMethods(Class<?> subscriberClass) {
    //首先查找緩存
    List<SubscriberMethod> subscriberMethods = METHOD_CACHE.get(subscriberClass);
    if (subscriberMethods != null) {
        return subscriberMethods;
    }
    //ignoreGeneratedIndex默認為false,表示是否忽略注解生成器
    if (ignoreGeneratedIndex) {
        subscriberMethods = findUsingReflection(subscriberClass);//通過反射獲取
    } else {
        subscriberMethods = findUsingInfo(subscriberClass);//通過注解的方式
    }
    if (subscriberMethods.isEmpty()) {//如果當前訂閱者沒有聲明訂閱方法粉渠，則拋出異常
    } else {
        //將訂閱者及訂閱方法存入緩存中
        METHOD_CACHE.put(subscriberClass, subscriberMethods);
        ...
    }
}

1.3.1 通過注解索引的方式獲取訂閱者的訂閱方法

findUsingInfo：獲取訂閱者信息分冈，并且對其父類進行向上查詢，最后將所有訂閱方法信息封裝到subscriberMethods列表中返回

 private List<SubscriberMethod> findUsingInfo(Class<?> subscriberClass) {
    FindState findState = prepareFindState();//通過對象池的方式復用FindState
    findState.initForSubscriber(subscriberClass);//初始化參數(shù)并將訂閱者類信息導入
    while (findState.clazz != null) {
         //獲取訂閱者信息
        findState.subscriberInfo = getSubscriberInfo(findState);
        //使用了注解索引
        if (findState.subscriberInfo != null) {
            SubscriberMethod[] array = findState.subscriberInfo.getSubscriberMethods();
            for (SubscriberMethod subscriberMethod : array) {
                if (findState.checkAdd(subscriberMethod.method, subscriberMethod.eventType)) {
                    findState.subscriberMethods.add(subscriberMethod);//將訂閱方法存入
                }
            }
        } else {
            //未使用注解索引霸株，通過反射查詢訂閱者的訂閱方法
            findUsingReflectionInSingleClass(findState);
        }
         // 將findState.clazz改為subscriberClass的父類Class雕沉，再進行遍歷
        findState.moveToSuperclass();
    }
    return getMethodsAndRelease(findState);//回收FindState對象到對象池中，并返回subscriberMethods列表
}
    
...
//實現(xiàn)對象池
private static final FindState[] FIND_STATE_POOL = new FindState[POOL_SIZE];// POOL_SIZE = 4;
private FindState prepareFindState() {
    synchronized (FIND_STATE_POOL) {
        for (int i = 0; i < POOL_SIZE; i++) {
            FindState state = FIND_STATE_POOL[i];
            if (state != null) {
                FIND_STATE_POOL[i] = null;
                return state;
            }
        }
    }
    return new FindState();
}

getSubscriberInfo：遍歷訂閱者索引去件，返回查找的訂閱者的信息

private SubscriberInfo getSubscriberInfo(FindState findState) {
    //上面已經(jīng)有一次判斷蘑秽，所以這個條件不會進入
    if (findState.subscriberInfo != null && findState.subscriberInfo.getSuperSubscriberInfo() != null) {
        SubscriberInfo superclassInfo = findState.subscriberInfo.getSuperSubscriberInfo();
        if (findState.clazz == superclassInfo.getSubscriberClass()) {
            return superclassInfo;
        }
    }
    //遍歷訂閱者索引，查找訂閱者的信息
    if (subscriberInfoIndexes != null) {
        for (SubscriberInfoIndex index : subscriberInfoIndexes) {
            SubscriberInfo info = index.getSubscriberInfo(findState.clazz);
            if (info != null) {
                return info;
            }
        }
    }
    return null;
}

FindState 主要用來輔助存儲訂閱者信息

static class FindState {
        final List<SubscriberMethod> subscriberMethods = new ArrayList<>();
        final Map<Class, Object> anyMethodByEventType = new HashMap<>();
        final Map<String, Class> subscriberClassByMethodKey = new HashMap<>();
        final StringBuilder methodKeyBuilder = new StringBuilder(128);
        ...
        void moveToSuperclass() { ... }// 修改findState.clazz為subscriberClass的父類Class
}

1.3.2 通過反射獲取訂閱者的訂閱方法

findUsingReflection

//FindState主要用來輔助存儲訂閱者信息
private List<SubscriberMethod> findUsingReflection(Class<?> subscriberClass) {
    FindState findState = prepareFindState();//通過對象池的方式復用FindState
    findState.initForSubscriber(subscriberClass);//初始化參數(shù)并將訂閱者類信息導入
    while (findState.clazz != null) {
        findUsingReflectionInSingleClass(findState);//通過反射查詢訂閱者的訂閱方法
        // 將findState.clazz改為subscriberClass的父類Class箫攀，再進行遍歷
        findState.moveToSuperclass();
    }
    return getMethodsAndRelease(findState);//回收FindState對象到對象池中肠牲，并返回subscriberMethods列表
}

findUsingReflectionInSingleClass：通過反射查詢訂閱者的訂閱方法

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();//獲取所有聲明方法
    } catch (Throwable th) {
        // Workaround for java.lang.NoClassDefFoundError
        methods = findState.clazz.getMethods();
        findState.skipSuperClasses = true;
    }
    for (Method method : methods) {
        int modifiers = method.getModifiers();
        
        //校驗方法修飾屬性，是否PUBLIC及MODIFIERS_IGNORE
        // MODIFIERS_IGNORE = Modifier.ABSTRACT | Modifier.STATIC | BRIDGE | SYNTHETIC;
        
        if ((modifiers & Modifier.PUBLIC) != 0 && (modifiers & MODIFIERS_IGNORE) == 0) {
            Class<?>[] parameterTypes = method.getParameterTypes();//校驗方法參數(shù)
            if (parameterTypes.length == 1) {
                //拿到注解信息
                Subscribe subscribeAnnotation = method.getAnnotation(Subscribe.class);
                if (subscribeAnnotation != null) {
                    Class<?> eventType = parameterTypes[0];
                    if (findState.checkAdd(method, eventType)) {
                        ThreadMode threadMode = subscribeAnnotation.threadMode();
                        //將訂閱方法及方法的注解信息封裝到列表中
                        findState.subscriberMethods.add(new SubscriberMethod(method, eventType, threadMode,
                                subscribeAnnotation.priority(), subscribeAnnotation.sticky()));
                    }
                }
            } else if (strictMethodVerification && method.isAnnotationPresent(Subscribe.class)) {
                 //拋出異常
            }
        } else if (strictMethodVerification && method.isAnnotationPresent(Subscribe.class)) {
            //拋出異常
        }
    }
}

1.4 注冊訂閱方法:

subscribe：將訂閱者和訂閱方法封裝成對象靴跛，并將相同事件類型的封裝對象根據(jù)事件優(yōu)先級封裝到CopyOnWriteArrayList集合中缀雳，再將事件類型和CopyOnWriteArrayList封裝到map集合中

Map<Object, List<Class<?>>> typesBySubscriber;
Map<Class<?>, CopyOnWriteArrayList<Subscription>> subscriptionsByEventType;
Map<Class<?>, Object> stickyEvents = new ConcurrentHashMap<>();

private void subscribe(Object subscriber, SubscriberMethod subscriberMethod) {
    Class<?> eventType = subscriberMethod.eventType;
    //將訂閱者和訂閱方法封裝成對象
    Subscription newSubscription = new Subscription(subscriber, subscriberMethod);
    //查詢出同樣事件類型的所有Subscription對象
    CopyOnWriteArrayList<Subscription> subscriptions = subscriptionsByEventType.get(eventType);

    //通過CopyOnWriteArrayList對訂閱事件對象按事件類型,按照優(yōu)先級進行存儲（同優(yōu)先級則插入末尾）,并校驗是否多次注冊（已注冊拋出異常）
    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;
        }
    }
    
    //將訂閱者對象和訂閱事件存儲對應存儲到map集合中
    List<Class<?>> subscribedEvents = typesBySubscriber.get(subscriber);
    if (subscribedEvents == null) {
        subscribedEvents = new ArrayList<>();
        typesBySubscriber.put(subscriber, subscribedEvents);
    }
    subscribedEvents.add(eventType);

    if (subscriberMethod.sticky) {//處理粘性事件
        if (eventInheritance) {
            // 迭代所有事件可能會導致很多粘性事件的效率低下，因此應該更改數(shù)據(jù)結構以允許更有效的查找
            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();
                    //對粘性事件進行通知
                    checkPostStickyEventToSubscription(newSubscription, stickyEvent);
                }
            }
        } else {
            Object stickyEvent = stickyEvents.get(eventType);
            checkPostStickyEventToSubscription(newSubscription, stickyEvent);
        }
    }
}

2. 發(fā)布通知消息

post：通過在ThreadLocal中封裝一個事件隊列梢睛，去添加和執(zhí)行相應的事件

public void post(Object event) {
    //在ThreadLocal中封裝一個線程狀態(tài)信息肥印，里面包含一個事件隊列
    PostingThreadState postingState = currentPostingThreadState.get();
    List<Object> eventQueue = postingState.eventQueue;
    eventQueue.add(event);//將任務添加到事件隊列

    if (!postingState.isPosting) {
        postingState.isMainThread = isMainThread();
        postingState.isPosting = true;
        if (postingState.canceled) {
            throw new EventBusException("Internal error. Abort state was not reset");
        }
        try {
            while (!eventQueue.isEmpty()) {
                //遍歷發(fā)送當前事件隊列
                postSingleEvent(eventQueue.remove(0), postingState);
            }
        } finally {
            postingState.isPosting = false;
            postingState.isMainThread = false;
        }
    }
}
private final ThreadLocal<PostingThreadState> currentPostingThreadState = new ThreadLocal<PostingThreadState>() {
        @Override
        protected PostingThreadState initialValue() {
            return new PostingThreadState();
        }
    };

postSingleEvent

private void postSingleEvent(Object event, PostingThreadState postingState) throws Error {
    Class<?> eventClass = event.getClass();
    boolean subscriptionFound = false;
    if (eventInheritance) {
        //遍歷查找它的父類添加到列表
        List<Class<?>> eventTypes = lookupAllEventTypes(eventClass);
        int countTypes = eventTypes.size();
        for (int h = 0; h < countTypes; h++) {
            Class<?> clazz = eventTypes.get(h);
            //發(fā)送該事件
            subscriptionFound |= postSingleEventForEventType(event, postingState, clazz);
        }
    } else {
        subscriptionFound = postSingleEventForEventType(event, postingState, eventClass);
    }
    ... //找不到事件時異常處理 NoSubscriberEvent
}

private boolean postSingleEventForEventType(Object event, PostingThreadState postingState, Class<?> eventClass) {
        CopyOnWriteArrayList<Subscription> subscriptions;
        synchronized (this) {
            //獲取對應的訂閱者
            subscriptions = subscriptionsByEventType.get(eventClass);
        }
        ...
        for (Subscription subscription : subscriptions) {
            postingState.event = event;
            postingState.subscription = subscription;
            boolean aborted = false;
            try {//通知訂閱者
                postToSubscription(subscription, event, postingState.isMainThread);
                aborted = postingState.canceled;
            } finally {
                ...//重置postingState屬性
            }
            if (aborted)break;
        }
        ...
    }

postToSubscription：通知訂閱者识椰，對于不同線程發(fā)布消息會調用相應的線程事件隊列去執(zhí)行

private void postToSubscription(Subscription subscription, Object event, boolean isMainThread) {
    switch (subscription.subscriberMethod.threadMode) {
        case POSTING:
            //通反射調用過訂閱者的方法
            invokeSubscriber(subscription, event);
            break;
        case MAIN:
            if (isMainThread) {
                invokeSubscriber(subscription, event);
            } else {
                //如果不是主線程，則加入到主線程執(zhí)行隊列中執(zhí)行深碱，mainThreadPoster繼承自Handler
                mainThreadPoster.enqueue(subscription, event);
            }
            break;
        case MAIN_ORDERED:
            if (mainThreadPoster != null) {
                mainThreadPoster.enqueue(subscription, event);
            } else {
                invokeSubscriber(subscription, event);
            }
            break;
        case BACKGROUND:
            if (isMainThread) {
                //如果不是后臺線程腹鹉，則加入到后臺線程行隊列中執(zhí)行
                backgroundPoster.enqueue(subscription, event);
            } else {
                invokeSubscriber(subscription, event);
            }
            break;
        case ASYNC:
            asyncPoster.enqueue(subscription, event);
            break;
        ...
    }
}
...
void invokeSubscriber(Subscription subscription, Object event) {
    ...
    subscription.subscriberMethod.method.invoke(subscription.subscriber, event);
}

3. 發(fā)布粘性通知

postSticky: 粘性事件會通過單獨的stickyEvents集合進行存儲，同時會在事件訂閱的時候進行check post敷硅，繼而實現(xiàn)粘性這一效果

 public void postSticky(Object event) {
        synchronized (stickyEvents) {
            stickyEvents.put(event.getClass(), event);
            //添加到粘性事件列表功咒，在上述注冊訂閱方法時，會通過列表去通知信息
        }
        // Should be posted after it is putted, in case the subscriber wants to remove immediately
        post(event);//發(fā)布通知绞蹦，當前已經(jīng)訂閱的訂閱者可以收到
    }
    
...

  private void subscribe(Object subscriber, SubscriberMethod subscriberMethod) {
    ...

    if (subscriberMethod.sticky) {//處理粘性事件
        if (eventInheritance) {
            // 迭代所有事件可能會導致很多粘性事件的效率低下力奋，因此應該更改數(shù)據(jù)結構以允許更有效的查找
            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();
                    //對粘性事件進行通知
                    checkPostStickyEventToSubscription(newSubscription, stickyEvent);
                }
            }
        } else {
            Object stickyEvent = stickyEvents.get(eventType);
            checkPostStickyEventToSubscription(newSubscription, stickyEvent);
        }
    }
}

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