上一节中提到了两个很重要的集合, 在注册的时候收集到了必要的信息 , 这一节我们来看看发送数据的具体实现
EventBus -- 基本使用
EventBus源码 -- 注册
EventBus源码 -- 发送消息
EventBus源码 -- 注销
EventBusd的发送消息
EventBus.getDefault().post(new MessageForFrag("来自activity的消息,你收到了么"));
- getDefalt方法不再赘述 , 获取一个单例的实例
- 查看post方法
public void post(Object event) {
// 首先拿到事件队列 , 将要发送的事件加入到队列中
PostingThreadState postingState = currentPostingThreadState.get();
List发送单个事件的方法postSingleEvent
private void postSingleEvent(Object event, PostingThreadState postingState) throws Error {
// 获取事件的类
Class eventClass = event.getClass();
boolean subscriptionFound = false;
//eventInheritance表示是否向上查找事件的父类,默认为true
if (eventInheritance) {
List> eventTypes = lookupAllEventTypes(eventClass);
int countTypes = eventTypes.size();
for (int h = 0; h < countTypes; h++) {
Class clazz = eventTypes.get(h);
// 发送事件 <点击该方法>
subscriptionFound |= postSingleEventForEventType(event, postingState, clazz);
}
} else {
subscriptionFound = postSingleEventForEventType(event, postingState, eventClass);
}
// 找不到事件的异常
if (!subscriptionFound) {
if (logNoSubscriberMessages) {
Log.d(TAG, "No subscribers registered for event " + eventClass);
}
if (sendNoSubscriberEvent && eventClass != NoSubscriberEvent.class &&
eventClass != SubscriberExceptionEvent.class) {
post(new NoSubscriberEvent(this, event));
}
}
}
当eventInheritance为true时，则通过lookupAllEventTypes找到所有的父类事件并存在List中，然后通过postSingleEventForEventType方法对事件逐一处理，接下来看看postSingleEventForEventType方法：
private boolean postSingleEventForEventType(Object event, PostingThreadState postingState, Class eventClass) {
CopyOnWriteArrayList subscriptions;
synchronized (this) {
// 通过事件类型找到所有的订阅方法
subscriptions = subscriptionsByEventType.get(eventClass);
}
if (subscriptions != null && !subscriptions.isEmpty()) {
// 遍历订阅方法 , 记录事件以及订阅方法
for (Subscription subscription : subscriptions) {
postingState.event = event;
postingState.subscription = subscription;
boolean aborted = false;
// 对每个订阅事件进行发送
try {
// <点击该方法>
postToSubscription(subscription, event, postingState.isMainThread);
aborted = postingState.canceled;
} finally {
postingState.event = null;
postingState.subscription = null;
postingState.canceled = false;
}
if (aborted) {
break;
}
}
return true;
}
return false;
}
到这里我们又看到了熟悉的那个集合: subscriptionsByEventType , 通过这个集合找到了事件类型对应的所有方法 , 然后将事件信息和方法保存在postingState中 ,调用postToSubscription发送给订阅方法
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 {
mainThreadPoster.enqueue(subscription, event);
}
break;
case BACKGROUND:
if (isMainThread) {
backgroundPoster.enqueue(subscription, event);
} else {
invokeSubscriber(subscription, event);
}
break;
case ASYNC:
asyncPoster.enqueue(subscription, event);
break;
default:
throw new IllegalStateException("Unknown thread mode: " + subscription.subscriberMethod.threadMode);
}
}
看到这里是不是熟悉了好多 ?四种线程模型的switch , 对应四种不同的处理, 无非就是加入队列和invokeSubscriber.
mainThreadPoster是HandlerPoster类型的继承自Handler，通过Handler将订阅方法切换到主线程执行。其他两种poster也都继承自Runnable接口 , 最终也都执行invokeSubscriber方法, 只是参数不一样了...这里拿MAIN中的方法来讲解.
void invokeSubscriber(Subscription subscription, Object event) {
try {
//通过反射获取到指定事件类型(参数)的订阅方法, 并调用
subscription.subscriberMethod.method.invoke(subscription.subscriber, event);
} catch (InvocationTargetException e) {
handleSubscriberException(subscription, event, e.getCause());
} catch (IllegalAccessException e) {
throw new IllegalStateException("Unexpected exception", e);
}
}
至此, post传入的事件就被相对应的订阅方法所接收.