EventBus事件总线组件：事件通知功能之事件注册

之前看过EventBus的源码，不是很深入，导致有些模糊，此次仔细阅读了一下，记录笔记，方便以后熟悉。
本篇主要说一下register的过程：

private synchronized void register(Object subscriber, boolean sticky, int priority) {
    //查找subscriber（执行register的类）中注册事件的方法，onEvent开头，参数只允许一个，超过一个将被忽略
   List subscriberMethods = subscriberMethodFinder.findSubscriberMethods(subscriber.getClass());
   for (SubscriberMethod subscriberMethod : subscriberMethods) {
       //根据事件类型以及订阅类进行数据处理
       subscribe(subscriber, subscriberMethod, sticky, priority);
   }
}

findSubscriberMethods这个方法很长，大致要做的事情就是查找出该类以及其父类中声明的所有方法，根据规则（只能public修饰onEvent开头且只有一个参数）筛选出订阅方法，一起看一下吧，具体就在代码中写说明了，删除了部分代码限制篇幅：

List findSubscriberMethods(Class subscriberClass) {
    //省略部分代码
   subscriberMethods = new ArrayList();
   Class clazz = subscriberClass;
   HashSet eventTypesFound = new HashSet();
   StringBuilder methodKeyBuilder = new StringBuilder();
   while (clazz != null) {
       String name = clazz.getName();
       //忽略系统类
       if (name.startsWith("java.") || name.startsWith("javax.") || name.startsWith("android.")) {
           break;
       }
       //获取该类中声明的所有方法
       Method[] methods = clazz.getDeclaredMethods();
       for (Method method : methods) {
           String methodName = method.getName();
           //是否以onEvent开头
           if (methodName.startsWith(ON_EVENT_METHOD_NAME)) {
               int modifiers = method.getModifiers();
               //修饰符只能以public开头
               if ((modifiers & Modifier.PUBLIC) != 0 && (modifiers & MODIFIERS_IGNORE) == 0) {
                   Class[] parameterTypes = method.getParameterTypes();
                   //只能有一个参数
                   if (parameterTypes.length == 1) {
                       String modifierString = methodName.substring(ON_EVENT_METHOD_NAME.length());
                       ThreadMode threadMode;
                       //获取线程执行方式
                       if (modifierString.length() == 0) {
                           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 {
                        //省略部分代码
                       }
                       Class eventType = parameterTypes[0];
                       methodKeyBuilder.setLength(0);
                       methodKeyBuilder.append(methodName).append('>').append(eventType.getName());
                       String methodKey = methodKeyBuilder.toString();
                       //检查是否已经添加过
                       if (eventTypesFound.add(methodKey)) {
                           // Only add if not already found in a sub class
                        //添加到列表中
                           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);
               }
           }
       }
       //获取父类并且继续查找父类中的订阅方法
       clazz = clazz.getSuperclass();
   }
   //省略部分代码
}

接下来看subscribe(subscriber, subscriberMethod, sticky, priority);这个方法是干啥的，总结来说就是把所有事件类型为eventType的订阅者放入List列表中，并放入Map集合中。然后再根据订阅事件的类构造一个订阅事件列表，用来判断某个类是否已经注册过事件,看一下代码：

private void subscribe(Object subscriber, SubscriberMethod subscriberMethod, boolean sticky, int priority) {
    //获取订阅事件中的时间类型
    Class eventType = subscriberMethod.eventType;
    //根据事件类型查找对应的所有订阅者（由类、方法、优先级组成）
    CopyOnWriteArrayList subscriptions = subscriptionsByEventType.get(eventType);
    //创建一个新的订阅者
    Subscription newSubscription = new Subscription(subscriber, subscriberMethod, priority);
    if (subscriptions == null) {
        subscriptions = new CopyOnWriteArrayList();
        //将订阅者列表放入Map中，后面post的时候会会根据这个eventType来获取该订阅者列表，然后来触发事件
        subscriptionsByEventType.put(eventType, subscriptions);
    } else {
        //不允许重复注册
        if (subscriptions.contains(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);
    //根据优先级将新的订阅者插入到已有的订阅者列表中
    int size = subscriptions.size();
    for (int i = 0; i <= size; i++) {
        if (i == size || newSubscription.priority > subscriptions.get(i).priority) {
            subscriptions.add(i, newSubscription);
            break;
        }
    }

    //根据订阅类查找该订阅类中订阅事件类型，isRegister方法会用到此Map，判断是否已经注册过事件
    List> subscribedEvents = typesBySubscriber.get(subscriber);
    if (subscribedEvents == null) {
        subscribedEvents = new ArrayList>();
        typesBySubscriber.put(subscriber, subscribedEvents);
    }
    subscribedEvents.add(eventType);

    //粘性事件
    if (sticky) {
        //指定粘性事件是否只触发订阅了当前事件类型的子类的订阅者
        if (eventInheritance) {
            //stickyEvents中key为事件类名，value为事件类的实例
            Set, Object>> entries = stickyEvents.entrySet();
            for (Map.Entry, Object> entry : entries) {
                Class candidateEventType = entry.getKey();
                //eventType类是否是candidateEventType类的父类
                if (eventType.isAssignableFrom(candidateEventType)) {
                    Object stickyEvent = entry.getValue();
                    //触发事件
                    checkPostStickyEventToSubscription(newSubscription, stickyEvent);
                }
            }
        } else {
            //获取所有黏性事件并触发
            Object stickyEvent = stickyEvents.get(eventType);
            checkPostStickyEventToSubscription(newSubscription, stickyEvent);
        }
    }
}

post某个事件时需要注意的一点是如果你post的事件类型为A，那么所有订阅过A的超类的事件也同样会被触发，时间原因，源码不分析，后续有时间接着写，记此笔记，方便自己查阅！