EventBus2.2源码分析

由于我们项目使用了EventBus2，所以查看一下源码，了解一下原理

关键的event缓存数据结构

    // 订阅方法，按event类型归类
    private final Map, CopyOnWriteArrayList> subscriptionsByEventType;
    // 缓存已经注册的对象，可防止对象重复注册
    private final Map>> typesBySubscriber;
    // 缓存粘性时间，用于使用registerSticky方法注册后立刻执行事件
    private final Map, Object> stickyEvents;

注册方法

   private synchronized void register(ClassLoader loader, String stuckClassName, Object subscriber, String methodName, boolean sticky, int priority) {
        //检查是否已经注册
        if (isRegistered(subscriber)){
            return;
        }
        List subscriberMethods = subscriberMethodFinder.findSubscriberMethods(loader, stuckClassName, subscriber.getClass(),
                methodName);
        for (SubscriberMethod subscriberMethod : subscriberMethods) {
            subscribe(subscriber, subscriberMethod, sticky, priority);
        }
    }

    public synchronized boolean isRegistered(Object subscriber) {
        return typesBySubscriber.containsKey(subscriber);
    }

查找方法

  List findSubscriberMethods(ClassLoader loader, String stuckClassName, Class subscriberClass, String eventMethodName) {
        String key = subscriberClass.getName() + '.' + eventMethodName;
        List subscriberMethods;
        synchronized (methodCache) {
            //获取之前缓存的方法，减少反射查询时间
            subscriberMethods = methodCache.get(key);
        }
        if (subscriberMethods != null) {
            return subscriberMethods;
        }
        subscriberMethods = new ArrayList();
        Class clazz = loadClass(loader, 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.")) {
                // 跳过系统方法
                break;
            }

            // Starting with EventBus 2.2 we enforced methods to be public (might change with annotations again)
            Method[] methods = clazz.getDeclaredMethods();
            for (Method method : methods) {
                String methodName = method.getName();
                //方法名字“onEvent”（默认）开头的，注册时传进来的
                if (methodName.startsWith(eventMethodName)) {
                    int modifiers = method.getModifiers();
                    // 公共，非抽象和静态
                    if ((modifiers & Modifier.PUBLIC) != 0 && (modifiers & MODIFIERS_IGNORE) == 0) {
                        Class[] parameterTypes = method.getParameterTypes();
                        //只有一个参数
                        if (parameterTypes.length == 1) {
                            //截取方法名字后面的字符串
                            String modifierString = methodName.substring(eventMethodName.length());
                            @ThreadMode int threadMode;
                            //区分将执行的线程
                            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 {
                                if (skipMethodVerificationForClasses.containsKey(clazz)) {
                                    continue;
                                } else {
                                    throw new EventBusException("Illegal onEvent method, check for typos: " + method);
                                }
                            }
                            Class eventType = parameterTypes[0];
                            methodKeyBuilder.setLength(0);
                            methodKeyBuilder.append(methodName);
                            methodKeyBuilder.append('>').append(eventType.getName());
                            //拼接key，方法名字+">"+参数类名
                            String methodKey = methodKeyBuilder.toString();
                            if (eventTypesFound.add(methodKey)) {
                                // 加入观测者列表
                                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);
                    }
                }
            }
            //对比查找类名，相同跳出方法
            if (name.equals(stuckClassName)) {
                break;
            }
            //搜索父类的方法
            clazz = loadClass(loader, clazz.getSuperclass());
        }
        if (subscriberMethods.isEmpty()) {
            //没有event方法将抛出异常
            throw new EventBusException("Subscriber " + subscriberClass + " has no public methods called "
                    + eventMethodName);
        } else {
            synchronized (methodCache) {
                //key：类名+"."+方法前缀（默认onEvent）
                //加入缓存方法
                methodCache.put(key, subscriberMethods);
            }
            return subscriberMethods;
        }
    }

订阅监听者

// 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envnt的方法列表，key为方法参数的类全名
        CopyOnWriteArrayList subscriptions = subscriptionsByEventType.get(eventType);
        Subscription newSubscription = new Subscription(subscriber, subscriberMethod, priority);
        if (subscriptions == null) {
            subscriptions = new CopyOnWriteArrayList();
            subscriptionsByEventType.put(eventType, subscriptions);
        } else {
            //检查重复注册
            for (Subscription subscription : subscriptions) {
                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++) {
            //插入订阅列表，优先级越高，排越签名，加优先执行
            if (i == size || newSubscription.priority > subscriptions.get(i).priority) {
                subscriptions.add(i, newSubscription);
                break;
            }
        }

        List> subscribedEvents = typesBySubscriber.get(subscriber);
        if (subscribedEvents == null) {
            subscribedEvents = new ArrayList>();
            typesBySubscriber.put(subscriber, subscribedEvents);
        }
        subscribedEvents.add(eventType);

        //执行粘性事件
        if (sticky) {
            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());
            }
        }
    }

发送事件

    public void post(Object event) {
        PostingThreadState postingState = currentPostingThreadState.get();
        List