EventBus – 9 源码解析-7：subscribe方法完成订阅（下）

最新推荐文章于 2024-06-15 23:13:15 发布

最新推荐文章于 2024-06-15 23:13:15 发布 · 263 阅读

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本文深入探讨了EventBus中的事件分发机制，特别是sticky事件的处理方式。针对不同线程模式下的事件传递流程进行了详细解释，并展示了如何根据不同场景选择合适的事件处理策略。

最核心的，分发事件
checkPostStickyEventToSubscription(newSubscription, stickyEvent);

我们跟进入看下这个方法，

private void checkPostStickyEventToSubscription(Subscription newSubscription, Object stickyEvent) {
        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, isMainThread());
        }
    }

private void postToSubscription(Subscription subscription, Object event, boolean isMainThread) {
        switch (subscription.subscriberMethod.threadMode) {
            case POSTING:
                invokeSubscriber(subscription, event);
                break;
            case MAIN:
                if (isMainThread) {
                    invokeSubscriber(subscription, event);
                } else {
                    // 如果不是在主线程，它会通过enqueue方法，录入到队列当中
                    mainThreadPoster.enqueue(subscription, event);
                }
                break;
            case MAIN_ORDERED:
                if (mainThreadPoster != null) {
                    mainThreadPoster.enqueue(subscription, event);
                } else {
                    // temporary: technically not correct as poster not decoupled from subscriber
                    invokeSubscriber(subscription, event);
                }
                break;
            case BACKGROUND:
                if (isMainThread) {
                    backgroundPoster.enqueue(subscription, event);
                } else {
                    // 如果不在UI线程会调用这个
                    invokeSubscriber(subscription, event);
                }
                break;
            case ASYNC:
                // 不管是否在主线程都会添加到这个队列当中
                asyncPoster.enqueue(subscription, event);
                break;
            default:
                throw new IllegalStateException("Unknown thread mode: " + subscription.subscriberMethod.threadMode);
        }
    }