我们来分析Eventbus3.0 的 post()方法
class-relation.png
subscriptionsByEventType : key 为订阅事件event Class , value 为 所有订阅者的数据 , 可以根据 EventType 查找订阅事件。
typesBySubscriber : key 为当前项目有哪些Java类 注册了事件 , value 为这些类都订阅了哪些接收方法 , 根据我们的订阅对象找到 EventType。
/** Posts the given event to the event bus. */
public void post(Object event) {
PostingThreadState postingState = currentPostingThreadState.get();
List<Object> eventQueue = postingState.eventQueue;
eventQueue.add(event);
if (!postingState.isPosting) {
postingState.isMainThread = Looper.getMainLooper() == Looper.myLooper();
postingState.isPosting = true;
if (postingState.canceled) {
throw new EventBusException("Internal error. Abort state was not reset");
}
try {
while (!eventQueue.isEmpty()) {
postSingleEvent(eventQueue.remove(0), postingState);
}
} finally {
postingState.isPosting = false;
postingState.isMainThread = false;
}
}
}
currentPostingThreadState 是一个 ThreadLocal 对象 他会在每个线程有自己的 PostingThreadState 没有存过就创建一个默认的对象;
final static class PostingThreadState {
//通过post方法参数传入的事件集合
final List<Object> eventQueue = new ArrayList<Object>();
boolean isPosting; //是否正在执行postSingleEvent()方法
boolean isMainThread;
Subscription subscription;
Object event;
boolean canceled;
}
PostingThreadState 封装了发送需要的一些数据
postSingleEvent()里会调用postSingleEventForEventType()
private boolean postSingleEventForEventType(Object event, PostingThreadState postingState, Class<?> eventClass) {
CopyOnWriteArrayList<Subscription> subscriptions;
synchronized (this) {
subscriptions = subscriptionsByEventType.get(eventClass);
}
if (subscriptions != null && !subscriptions.isEmpty()) {
for (Subscription subscription : subscriptions) {
postingState.event = event;
postingState.subscription = subscription;
boolean aborted = false;
try {
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;
}
subscriptionsByEventType
key 事件类型
value 接收的事件的方法List
postToSubscription()
会根据不同的线程来执行不同的方法向订阅者发送事件其中invokeSubscriber() 是根据方法名来反射操作的;
unregister
/** Unregisters the given subscriber from all event classes. */
public synchronized void unregister(Object subscriber) {
List<Class<?>> subscribedTypes = typesBySubscriber.get(subscriber);
if (subscribedTypes != null) {
for (Class<?> eventType : subscribedTypes) {
unsubscribeByEventType(subscriber, eventType);
}
typesBySubscriber.remove(subscriber);
} else {
Log.w(TAG, "Subscriber to unregister was not registered before: " + subscriber.getClass());
}
}
typesBySubscriber
是个map key 为我们传入的this 也就是当前类
value是当前类所有接收事件方法class类型
/** Only updates subscriptionsByEventType, not typesBySubscriber! Caller must update typesBySubscriber. */
private void unsubscribeByEventType(Object subscriber, Class<?> eventType) {
List<Subscription> subscriptions = subscriptionsByEventType.get(eventType);
if (subscriptions != null) {
int size = subscriptions.size();
for (int i = 0; i < size; i++) {
Subscription subscription = subscriptions.get(i);
if (subscription.subscriber == subscriber) {
subscription.active = false;
subscriptions.remove(i);
i--;
size--;
}
}
}
}
subscriptionsByEventType map对象 , 根据我们的eventType 来取出订阅这个事件所有方法, 判断是当前要取消注册这个事件的元素就在集合remove掉;
总结 :
发送过程
- 利用localThread来实现取出当前线程的封装收
- 循环一个map取出当前事件的所有订阅者
- 利用反射发送事件
取消注册逻辑
- 利用2个map判断其事件类型,来移除要解注册元素
注册逻辑
- 利用SubscriberMethodFinder 对象来取出 List<SubscriberMethod> 集合,他是查看当前类有哪些接收事件
- 然后遍历他,把接收事件的方法 存入2个总的map中;
注意
1.eventBus 不要多次注册,否则会导致方法接收被多次调用
