EventBus 索引SampleBusIndex

最新推荐文章于 2025-02-04 16:19:10 发布

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最新推荐文章于 2025-02-04 16:19:10 发布

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分类专栏：源码学习 EventBus 文章标签： EventBus

本文链接：https://blog.youkuaiyun.com/xiey94/article/details/82967346

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EventBus

9 篇文章

订阅专栏

本文深入探讨EventBus的索引机制，详细解释如何通过索引优化事件注册过程，提高事件处理效率。从EventBusBuilder的addIndex方法入手，分析索引如何被加载并应用于SubscriberMethodFinder中，以加速查找订阅方法。

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EventBus 索引SampleBusIndex

// 加载索引，添加到默认配置的EventBus
EventBus.builder().addIndex(new SampleBusIndex()).installDefaultEventBus();

/** Adds an index generated by EventBus' annotation preprocessor. */
public EventBusBuilder addIndex(SubscriberInfoIndex index) {
    if (subscriberInfoIndexes == null) {
        subscriberInfoIndexes = new ArrayList<>();
    }
    subscriberInfoIndexes.add(index);
    return this;
}

把索引信息添加到了subscriberInfoIndexes中；

初始化的时候

EventBus(EventBusBuilder builder) {
        ......
        indexCount = builder.subscriberInfoIndexes != null ? builder.subscriberInfoIndexes.size() : 0;
        subscriberMethodFinder = new SubscriberMethodFinder(builder.subscriberInfoIndexes,builder.strictMethodVerification, builder.ignoreGeneratedIndex);
        ......
    }

indexCount获取了索引个数，将索引信息传到了SubscriberMethodFinder；

SubscriberMethodFinder我们是在register的时候用到的，用于寻找所有的订阅方法；

public void register(Object subscriber) {
    Class<?> subscriberClass = subscriber.getClass();
    List<SubscriberMethod> subscriberMethods = subscriberMethodFinder.findSubscriberMethods(subscriberClass);
    synchronized (this) {
        for (SubscriberMethod subscriberMethod : subscriberMethods) {
            subscribe(subscriber, subscriberMethod);
        }
    }
}

在SubscriberMethodFinder中是怎么用到的呢？

List<SubscriberMethod> findSubscriberMethods(Class<?> subscriberClass) {
        List<SubscriberMethod> subscriberMethods = METHOD_CACHE.get(subscriberClass);
        if (subscriberMethods != null) {
            return subscriberMethods;
        }

        if (ignoreGeneratedIndex) {
            subscriberMethods = findUsingReflection(subscriberClass);
        } else {
            subscriberMethods = findUsingInfo(subscriberClass);
        }
        if (subscriberMethods.isEmpty()) {
            throw new EventBusException("Subscriber " + subscriberClass
                    + " and its super classes have no public methods with the @Subscribe annotation");
        } else {
            METHOD_CACHE.put(subscriberClass, subscriberMethods);
            return subscriberMethods;
        }
    }

有一个ignoreGeneratedIndex，默认不赋值，也就是默认false；

subscriberMethods = findUsingInfo(subscriberClass);

private List<SubscriberMethod> findUsingInfo(Class<?> subscriberClass) {
        FindState findState = prepareFindState();
        findState.initForSubscriber(subscriberClass);
        while (findState.clazz != null) {
            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 {
                findUsingReflectionInSingleClass(findState);
            }
            findState.moveToSuperclass();
        }
        return getMethodsAndRelease(findState);
    }

private SubscriberInfo getSubscriberInfo(FindState findState) {
        if (findState.subscriberInfo != null && findState.subscriberInfo.getSuperSubscriberInfo() != null) {
            SubscriberInfo superclassInfo = findState.subscriberInfo.getSuperSubscriberInfo();
            if (findState.clazz == superclassInfo.getSubscriberClass()) {
                return superclassInfo;
            }
        }
        if (subscriberInfoIndexes != null) {
            for (SubscriberInfoIndex index : subscriberInfoIndexes) {
                SubscriberInfo info = index.getSubscriberInfo(findState.clazz);
                if (info != null) {
                    return info;
                }
            }
        }
        return null;
    }

getSubscriberInfo方法中，满足if (subscriberInfoIndexes != null) 条件，所以返回订阅者信息；

所以findUsingInfo方法中没有设置索引的时候走的是findUsingReflectionInSingleClass(findState);现在走的是上面的if语句块

if (findState.subscriberInfo != null) {
    SubscriberMethod[] array = findState.subscriberInfo.getSubscriberMethods();
    for (SubscriberMethod subscriberMethod : array) {
        if (findState.checkAdd(subscriberMethod.method, subscriberMethod.eventType)) {
            findState.subscriberMethods.add(subscriberMethod);
        }
    }
}

找到该订阅者中所有的订阅方法，开始检查，后续和之前的普通方法register一样；
EventBus 普通事件register