EventBus源码解析04-取消订阅

冷不防 2023-10-17 15:23 125阅读 0赞

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; 
    }