EventBus源码解析04-取消订阅

取消订阅会调用unregister()

public synchronized void unregister(Object subscriber) {
    //根据subscriber获取eventType集合
    List<Class<?>> subscribedTypes = typesBySubscriber.get(subscriber);
    if (subscribedTypes != null) {
        //遍历eventType集合
        for (Class<?> eventType : subscribedTypes) {
            unsubscribeByEventType(subscriber, eventType);
        }
        typesBySubscriber.remove(subscriber);
    } else {
        Log.w(TAG, "Subscriber to unregister was not registered before: " + subscriber.getClass());
    }
}  

可以看到，这里会根据subscriber获取eventType集合，再遍历这个集合逐个调用unsubscribeByEventType

private void unsubscribeByEventType(Object subscriber, Class<?> eventType) {
    //根据eventType获取Subscription(被观察者)集合
    List<Subscription> subscriptions = subscriptionsByEventType.get(eventType);
    if (subscriptions != null) {
        int size = subscriptions.size();
        //遍历subscriptions集合
        for (int i = 0; i < size; i++) {
            Subscription subscription = subscriptions.get(i);
            //判断subscriber是否相同
            if (subscription.subscriber == subscriber) {
                subscription.active = false;
                //移除被观察者
                subscriptions.remove(i);
                i--;
                size--;
            }
        }
    }
}  

这里，会根据eventType获取Subscription(被观察者)集合，在遍历subscriptions集合，找到和传入的subscriber相同的对象，将其从subscriptions集合中移除，从而取消订阅。

总结

EventBus的取消订阅主要就是根据传入的subscriber，把相应的被观察者(Subscription)从subscriptions集合(之前注册的时候所存放的集合)中移除。

final class Subscription {
    //@Subscribe所在的类
    final Object subscriber;
    //@Subscribe注解的方法
    final SubscriberMethod subscriberMethod; 
}