// EventType -> List<Subscription>，事件到订阅之间的映射  //这里用了CopyOnWriteArrayList ,为何这么做呢?需要留意下
private final Map<Class<?>, CopyOnWriteArrayList<Subscription>> subscriptionsByEventType;

// Subscriber -> List<EventType>，订阅者到它订阅的的所有事件类型的映射
private final Map<Object, List<Class<?>>> typesBySubscriber;

// stickEvent事件，后面会看到
private final Map<Class<?>, Object> stickyEvents;

// EventType -> List<? extends EventType>，事件到它的父事件列表的映射。即缓存一个类的所有父类
private static final Map<Class<?>, List<Class<?>>> eventTypesCache = new HashMap<Class<?>, List<Class<?>>>();

/** Convenience singleton for apps using a process-wide EventBus instance. */
    public static EventBus getDefault() {
        //默认的单例模式
        if (defaultInstance == null) {
            synchronized (EventBus.class) {
                if (defaultInstance == null) {
                    defaultInstance = new EventBus();
                }
            }
        }
        return defaultInstance;
    }

public void register(Object subscriber) {
        //官方推荐使用此方法,这样默认订阅者就是默认的四个
        register(subscriber, DEFAULT_METHOD_NAME, false, 0);
    }

public void register(Object subscriber, int priority) {
        register(subscriber, DEFAULT_METHOD_NAME, false, priority);
    }

    @Deprecated
 public void register(Object subscriber, String methodName) {
        //也可以这样注册,添加订阅这的方法名,但已经飞起了
        register(subscriber, methodName, false, 0);
    }


public void registerSticky(Object subscriber) {
        register(subscriber, DEFAULT_METHOD_NAME, true, 0);
    }


public void registerSticky(Object subscriber, int priority) {
        register(subscriber, DEFAULT_METHOD_NAME, true, priority);
    }
//

  /**
     *
     * @param subscriber 订阅者
     * @param methodName 订阅者方法明,一般为默认
     * @param sticky  //是否为粘性事件,一般为false,如果使用,一般要调用 registerSticky 方法
     * @param priority   事件的优先级,一般为默认 0
     */
    private synchronized void register(Object subscriber, String methodName, boolean sticky, int priority) {
        //这里的重点 1: findSubsrciberMethods 方法
        List<SubscriberMethod> subscriberMethods = subscriberMethodFinder.findSubscriberMethods(subscriber.getClass(),
                methodName);
        for (SubscriberMethod subscriberMethod : subscriberMethods) {
            //这里的重点 2: 生成订阅
            subscribe(subscriber, subscriberMethod, sticky, priority);
        }
    }

private static final int MODIFIERS_IGNORE = Modifier.ABSTRACT | Modifier.STATIC;
    //方法缓存,这样不需要每次都去透过反射获取方法
    private static final Map<String, List<SubscriberMethod>> methodCache = new HashMap<String, List<SubscriberMethod>>();

    private static final Map<Class<?>, Class<?>> skipMethodVerificationForClasses = new ConcurrentHashMap<Class<?>, Class<?>>();

    List<SubscriberMethod> findSubscriberMethods(Class<?> subscriberClass, String eventMethodName) {
        String key = subscriberClass.getName() + ‘.‘ + eventMethodName;
        List<SubscriberMethod> subscriberMethods;
        synchronized (methodCache) {
            //优先读取缓存
            subscriberMethods = methodCache.get(key);
        }
        if (subscriberMethods != null) {
            //有缓存,则直接返回,这样的话,就不用每次使用时都去通过下面的反射方法查找
            return subscriberMethods;
        }
        subscriberMethods = new ArrayList<SubscriberMethod>();
        Class<?> clazz = subscriberClass;
        HashSet<String> eventTypesFound = new HashSet<String>();
        StringBuilder methodKeyBuilder = new StringBuilder();
        while (clazz != null) {
            String name = clazz.getName();
            if (name.startsWith("java.") || name.startsWith("javax.") || name.startsWith("android.")) {
                // Skip system classes, this just degrades performance
                //过滤掉系统的类
                break;
            }

            // Starting with EventBus 2.2 we enforced methods to be public (might change with annotations again)
            //获取订阅这的所有方法
            Method[] methods = clazz.getMethods();
            for (Method method : methods) {
                String methodName = method.getName();
                if (methodName.startsWith(eventMethodName)) {
                    //只找以 eventMethodName 开头的方法
                    int modifiers = method.getModifiers();
                    if ((modifiers & Modifier.PUBLIC) != 0 && (modifiers & MODIFIERS_IGNORE) == 0) {
                        //只找public 的方法 不接受 final ,static 的修饰符的方法
                        Class<?>[] parameterTypes = method.getParameterTypes();
                        // 获取方法中的参数,也就是event--object
                        if (parameterTypes.length == 1) {
                            //  ==1 说明 订阅者的方法,参数只能有一个,就是event
                            // 获取 onEvent(或者你本人注册时加入的方法)后面的内容,来判断ThreadMode 4种
                            String modifierString = methodName.substring(eventMethodName.length());
                            ThreadMode threadMode;
                            if (modifierString.length() == 0) {
                                //所以,如果不是按照onevent写法的话,默认的事件处理都是postThread,这点需要注意
                                threadMode = ThreadMode.PostThread;
                            } else if (modifierString.equals("MainThread")) {
                                threadMode = ThreadMode.MainThread;
                            } else if (modifierString.equals("BackgroundThread")) {
                                threadMode = ThreadMode.BackgroundThread;
                            } else if (modifierString.equals("Async")) {
                                threadMode = ThreadMode.Async;
                            } else {
                                if (skipMethodVerificationForClasses.containsKey(clazz)) {
                                    continue;
                                } else {
                                    throw new EventBusException("Illegal onEvent method, check for typos: " + method);
                                }
                            }
                            Class<?> eventType = parameterTypes[0];//获取event的类型
                            methodKeyBuilder.setLength(0);
                            methodKeyBuilder.append(methodName);
                            methodKeyBuilder.append(‘>‘).append(eventType.getName());
                            String methodKey = methodKeyBuilder.toString();
                            if (eventTypesFound.add(methodKey)) {
                                // Only add if not already found in a sub class
                                //封装一个订阅者方法的对象,包括 method,threadmode,eventType
                                subscriberMethods.add(new SubscriberMethod(method, threadMode, eventType));
                            }
                        }
                    } else if (!skipMethodVerificationForClasses.containsKey(clazz)) {
                        Log.d(EventBus.TAG, "Skipping method (not public, static or abstract): " + clazz + "."
                                + methodName);
                    }
                }
            }

            //再继续查找基类
            clazz = clazz.getSuperclass();
//所有事件处理方法**必需是`public void`类型**的，并且只有一个参数表示*EventType*。
//findSubscriberMethods`不只查找*Subscriber*内的事件处理方法，**同时还会查到它的继承体系中的所有基类中的事件处理方法**

        }
        if (subscriberMethods.isEmpty()) {
            throw new EventBusException("Subscriber " + subscriberClass + " has no public methods called "
                    + eventMethodName);
        } else {
            synchronized (methodCache) {
                //存入到缓存
                methodCache.put(key, subscriberMethods);
            }
            return subscriberMethods;
        }
    }

 // Must be called in synchronized block
    private void subscribe(Object subscriber, SubscriberMethod subscriberMethod, boolean sticky, int priority) {
        subscribed = true;
        Class<?> eventType = subscriberMethod.eventType; //获取订阅事件类型
        //根据订阅事件,找出所有订阅该事件的订阅(包括订阅者,订阅方法),生成订阅列表,也属于缓存
        CopyOnWriteArrayList<Subscription> subscriptions = subscriptionsByEventType.get(eventType);
        //生成一个新的订阅
        Subscription newSubscription = new Subscription(subscriber, subscriberMethod, priority);
        if (subscriptions == null) {
            //如果没有订阅列表,这创建,并添加新的订阅,此处订阅列表并不需要根据优先级来排序
            subscriptions = new CopyOnWriteArrayList<Subscription>();
            subscriptionsByEventType.put(eventType, subscriptions);
        } else {
            for (Subscription subscription : subscriptions) {
                //否则判断新的订阅是否已经加入订阅列表了
                if (subscription.equals(newSubscription)) {
                    throw new EventBusException("Subscriber " + subscriber.getClass() + " already registered to event "
                            + eventType);
                }
            }
        }

        // Starting with EventBus 2.2 we enforced methods to be public (might change with annotations again)
        // subscriberMethod.method.setAccessible(true);

        int size = subscriptions.size();
        for (int i = 0; i <= size; i++) {
            //根据优先级,来插入订阅
            if (i == size || newSubscription.priority > subscriptions.get(i).priority) {
                subscriptions.add(i, newSubscription);
                break;
            }
        }

        List<Class<?>> subscribedEvents = typesBySubscriber.get(subscriber);
        //将这个订阅事件放到订阅者的订阅列表中去
        if (subscribedEvents == null) {
            subscribedEvents = new ArrayList<Class<?>>();
            typesBySubscriber.put(subscriber, subscribedEvents);
        }
        subscribedEvents.add(eventType);



        if (sticky) {
            //如果是粘性订阅的话,直接发送上一个保存的事件(如果存在的话)
            Object stickyEvent;
            synchronized (stickyEvents) {
                stickyEvent = stickyEvents.get(eventType);
            }
            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());
            }
        }

// 根据`SubscriberMethod`中的*EventType*类型将`Subscribtion`对象存放在`subscriptionsByEventType`中。
//        建立*EventType*到*Subscription*的映射，每个事件可以有多个订阅者。
// 根据`Subscriber`将`EventType`存放在`typesBySubscriber`中，建立*Subscriber*到*EventType*的映射，
//        每个Subscriber可以订阅多个事件。
// 如果是*Sticky*类型的订阅者，直接向它发送上个保存的事件（如果有的话）。

//        通过*Subscriber*到*EventType*的映射，我们就可以很方便地使一个Subscriber取消接收事件，
//        通过*EventType*到*Sucscribtion*的映射，可以方便地将相应的事件发送到它的每一个订阅者。

    }

   /** Posts the given event to the event bus. */
    public void post(Object event) {
        //获取threadLocal 这里是个ThreadLocal 要值得注意哦
        PostingThreadState postingState = currentPostingThreadState.get();
        //将事件添加到队列中
        List<Object> eventQueue = postingState.eventQueue;
        eventQueue.add(event);

        if (postingState.isPosting) {
            return;
        } else {
            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()) {
                    //逐个发送消息
                    postSingleEvent(eventQueue.remove(0), postingState);
                }
            } finally {
                postingState.isPosting = false;
                postingState.isMainThread = false;
            }
        }
    }

final static class PostingThreadState {
    List<Object> eventQueue = new ArrayList<Object>();
    boolean isPosting;
    boolean isMainThread;
    Subscription subscription;
    Object event;
    boolean canceled;
}

{
        //根据event 获取 class
        Class<? extends Object> eventClass = event.getClass();
        // 根据刚才获取的class 获取 类的对象,借口以及父类等
        List<Class<?>> eventTypes = findEventTypes(eventClass);
        boolean subscriptionFound = false;
        int countTypes = eventTypes.size();
        for (int h = 0; h < countTypes; h++) {
            Class<?> clazz = eventTypes.get(h);
            CopyOnWriteArrayList<Subscription> subscriptions;
            synchronized (this) {
                //找到订阅事件对应的订阅 ,(之前在register中添加的)
                subscriptions = subscriptionsByEventType.get(clazz);
            }
            if (subscriptions != null && !subscriptions.isEmpty()) {
                for (Subscription subscription : subscriptions) {
                    postingState.event = event;
                    postingState.subscription = subscription;
                    boolean aborted = false;
                    try {
                        //向所有订阅改事件的订阅这发送消息( 如果有个事件订阅了 object 类型,那么就应该接受到了所有的消息)
                        postToSubscription(subscription, event, postingState.isMainThread);
                        aborted = postingState.canceled;
                    } finally {
                        postingState.event = null;
                        postingState.subscription = null;
                        postingState.canceled = false;
                    }
                    if (aborted) {
                        break;
                    }
                }
                subscriptionFound = true;
            }
        }
        if (!subscriptionFound) {
            Log.d(TAG, "No subscribers registered for event " + eventClass);
            if (eventClass != NoSubscriberEvent.class && eventClass != SubscriberExceptionEvent.class) {
                post(new NoSubscriberEvent(this, event));
            }
        }
    }

private void postToSubscription(Subscription subscription, Object event, boolean isMainThread) {
        switch (subscription.subscriberMethod.threadMode) {
        case PostThread:
            //如果是post,则在本线程中调用
            invokeSubscriber(subscription, event);
            break;
        case MainThread:
            if (isMainThread) {
                //如果目前是主线程,则直接调用
                invokeSubscriber(subscription, event);
            } else {
                //如果目前不是主线程,这放到主线程的handler中处理
                mainThreadPoster.enqueue(subscription, event);
            }
            break;
        case BackgroundThread:
            if (isMainThread) {
                //如果目前是主线程,则放runnable 线程池中
                backgroundPoster.enqueue(subscription, event);
            } else {
                //如果已经是子线程,则直接调用
                invokeSubscriber(subscription, event);
            }
            break;
        case Async:
            //直接放入到线程池中
            asyncPoster.enqueue(subscription, event);
            break;
        default:
            throw new IllegalStateException("Unknown thread mode: " + subscription.subscriberMethod.threadMode);
        }
    }