EventBus源码分析笔记

1.EventBus基本使用步骤

(1)Git地址:https://github.com/greenrobot/EventBus
(2)引入:compile 'org.greenrobot:eventbus:3.1.1'
(3)注册:
　onCreate/onStart 中

EventBus.getDefault().register(this);

onStop/onDestory中

EventBus.getDefault().unregister(this);

(4)发送事件

EventBus.getDefault().post("我是来自2的信息");

2.源码解读

(1)EventBus.getDefault() 单利设计模式

     public static EventBus getDefault() {
      if (defaultInstance == null) {
          synchronized (EventBus.class) {
              if (defaultInstance == null) {
                  defaultInstance = new EventBus();
              }
          }
      }
      return defaultInstance;
  }

(2)EventBus.getDefault().register(this);

public void register(Object subscriber) {
    //获取被观察者的class对象
    Class subscriberClass = subscriber.getClass();
    //根据class对象得到观察者方法集合
    List subscriberMethods = subscriberMethodFinder.findSubscriberMethods(subscriberClass);
    synchronized (this) {
        //遍历找到的观察者方法集合并信息遍历订阅
        for (SubscriberMethod subscriberMethod : subscriberMethods) {
                subscribe(subscriber, subscriberMethod);
        }
    }
}

List findSubscriberMethods(Class subscriberClass) {
        //先从缓存中寻找改观察者对象class对应的观察者方法集合
        List subscriberMethods = METHOD_CACHE.get(subscriberClass);
        //如果缓存中存在就直接返回
        if (subscriberMethods != null) {
            return subscriberMethods;
        }
        //这个参数取决于是否使用了编译时注解，类似ButterKnife，
        //我们一般不会引入eventbus的apt所以这个参数默认为false
        if (ignoreGeneratedIndex) {
            //使用了apt会走这里
            subscriberMethods = findUsingReflection(subscriberClass);
        } else {
            //一般情况下会到这里
            subscriberMethods = findUsingInfo(subscriberClass);
        }
        if (subscriberMethods.isEmpty()) {
            //这里比较奇葩，如果注入了EventBus但是不用的话
            //会直接给你抛异常，也就是说注册了则至少要有一个
            //subcriber注释修饰的public方法才行
            throw new EventBusException("Subscriber " + subscriberClass
                    + " and its super classes have no public methods with the @Subscribe annotation");
        } else {
            //保存到内存缓存
            METHOD_CACHE.put(subscriberClass, subscriberMethods);
            return subscriberMethods;
        }
    }

private List findUsingInfo(Class subscriberClass) {
        //准备一个查找状态对象，这里就是状态的存储封装，
        //这里面用了享元设计模式，不用太关注
        FindState findState = prepareFindState();
        //根据观察者class对象初始化状态对象
        findState.initForSubscriber(subscriberClass);
        while (findState.clazz != null) {
            //这里在没有使用apt时getSubscriberInfo返回的是null，细节自己看吧
            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 {
                //进入核心查找方法
                findUsingReflectionInSingleClass(findState);
            }
            findState.moveToSuperclass();
        }
        //返回找到并封装好的List，然后释放findState
       //这个方法里面会进行享元存储
        return getMethodsAndRelease(findState);
    }

/**
 * 通过反射查找观察者方法集合，放入查找状态存储对象中
 */
private void findUsingReflectionInSingleClass(FindState findState) {
        Method[] methods;
        try {
            // This is faster than getMethods, especially when subscribers are fat classes like Activities
            //获取观察者对象的所有方法
            //这里补充一点
            //getDeclaredMethods()得到该类所有方法，
                //包括私有以及接口实现的方法，但是不包括继承的
           //getMethods()得到所有public方法，包括接口实现及父类的
           //所以作者在这里说用getDeclaredMethods()比用getMethods()要快，
           //特别是Activities对象时
            methods = findState.clazz.getDeclaredMethods();
        } catch (Throwable th) {
            // Workaround for java.lang.NoClassDefFoundError, see https://github.com/greenrobot/EventBus/issues/149
           //出问题了，获取缓存的并跳过父类
            methods = findState.clazz.getMethods();
            findState.skipSuperClasses = true;
        }
        //遍历得到的所有方法
        for (Method method : methods) {
            //得到方法属性
            int modifiers = method.getModifiers();
            //判断是否为PUBLIC，
            //MODIFIERS_IGNORE 包含（抽象，静态，桥接,合成,后2者是编译器添加的）
            //这个if翻译过来就是这个方法必须是公共的，且不能是静态的和抽象的
            if ((modifiers & Modifier.PUBLIC) != 0 && (modifiers & MODIFIERS_IGNORE) == 0) {
                Class[] parameterTypes = method.getParameterTypes();
                //参数数量必须为1，否则也会抛异常
                if (parameterTypes.length == 1) {
                    //获取方法上的Subscribe注解对象
                    Subscribe subscribeAnnotation = method.getAnnotation(Subscribe.class);
                    if (subscribeAnnotation != null) {
                        //获取参数class
                        Class eventType = parameterTypes[0];
                       //这里确保的是不重复添加同意事件类型
                        if (findState.checkAdd(method, eventType)) {
                            ThreadMode threadMode = subscribeAnnotation.threadMode();
                            //将注解中的threadMode，priority，sticky
                            //和method，eventType对象封装成SubscriberMethod对象
                            //这里整个观察者的方法就找好了。
                            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");
            }
        }
    }

// Must be called in synchronized block
/**
  *  订阅
  *  解析所有的SubscriberMethod，最终放到
  * private final Map,CopyOnWriteArrayList> subscriptionsByEventType;
  */
private void subscribe(Object subscriber, SubscriberMethod subscriberMethod) {
        //时间类型的class对象，例如post("aaaa")，对应的eventType为String.class
        Class eventType = subscriberMethod.eventType;
        //封装成Subscription
        Subscription newSubscription = new Subscription(subscriber, subscriberMethod);
        //从subscriptionsByEventType获取eventType对应的Subscription
        CopyOnWriteArrayList subscriptions = subscriptionsByEventType.get(eventType);
        if (subscriptions == null) {
            //如果不存在新建后put
            subscriptions = new CopyOnWriteArrayList<>();
            subscriptionsByEventType.put(eventType, subscriptions);
        } else {
            //如果存在，且包含则跑出不能重复添加的异常
            if (subscriptions.contains(newSubscription)) {
                throw new EventBusException("Subscriber " + subscriber.getClass() + " already registered to event "
                        + eventType);
            }
        }
        //按照优先级进行将newSubscription添加到subscriptions
        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;
            }
        }
        //typesBySubscriber 存储的是观察者对象和事件类型的接口的map
        //key   观察者  例如MainActivity对象
        //value  post时的事件类型  如String.class
        List> subscribedEvents = typesBySubscriber.get(subscriber);
        if (subscribedEvents == null) {
            subscribedEvents = new ArrayList<>();
            typesBySubscriber.put(subscriber, subscribedEvents);
        }
        subscribedEvents.add(eventType);
       //处理粘性事件。。。没看懂
        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).
                Set, Object>> entries = stickyEvents.entrySet();
                for (Map.Entry, 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);
            }
        }
    }
//注册工作到此全部完成

(3)EventBus.getDefault().post("")

public void post(Object event) {
        //一个线程一个PostingThreadState对象
        PostingThreadState postingState = currentPostingThreadState.get();
      //添加到时间队列
        List