EventBus 原始碼分析（下篇）
摘要：
上篇EventBus 原始碼分析（上篇）
說到註冊訂閱的前半部分，此篇用來分析傳送事件到接收事件這個過程。
1. 傳送事件
示例：
EventBus.getDefault().post(new RemindBean("2018-02-1...
上篇ofollow,noindex">EventBus 原始碼分析（上篇） 說到註冊訂閱的前半部分，此篇用來分析傳送事件到接收事件這個過程。
1. 傳送事件
示例：
EventBus.getDefault().post(new RemindBean("2018-02-12","happy"));
post
:
/** Posts the given event to the event bus. */
public void post(Object event) {
- 1.獲取當前執行緒的postingThreadState 物件
PostingThreadState postingState = currentPostingThreadState.get();
- 2. 獲取裡面那個事件佇列
List<Object> eventQueue = postingState.eventQueue;
- 3. 將事件新增到佇列中去
eventQueue.add(event);
- 4. 判斷當前的event 是否在 posting
if (!postingState.isPosting) {
- 5. 是否是主執行緒
postingState.isMainThread = Looper.getMainLooper() == Looper.myLooper();
postingState.isPosting = true;
- 6. 判斷是否取消
if (postingState.canceled) {
throw new EventBusException("Internal error. Abort state was not reset");
}
try {
while (!eventQueue.isEmpty()) {//不為空，進入迴圈
- 7.按照順序，post一個 remove一個
postSingleEvent(eventQueue.remove(0), postingState);
}
} finally {
postingState.isPosting = false;
postingState.isMainThread = false;
}
}
}
PostingThreadState
大概看一眼
final static class PostingThreadState {
final List<Object> eventQueue = new ArrayList<Object>();
boolean isPosting;
boolean isMainThread;
Subscription subscription;
Object event;
boolean canceled;
}
再就是postSingleEvent(eventQueue.remove(0), postingState);
方法：
private void postSingleEvent(Object event, PostingThreadState postingState) throws Error {
- 1. 獲取event的位元組碼（例如就是：RemindBean.class）
Class<?> eventClass = event.getClass();
boolean subscriptionFound = false;
if (eventInheritance) {//預設為true
- 2. 根據eventClass 的位元組碼查詢
List<Class<?>> eventTypes = lookupAllEventTypes(eventClass);
int countTypes = eventTypes.size();
- 3.迴圈遍歷
for (int h = 0; h < countTypes; h++) {
Class<?> clazz = eventTypes.get(h);
- 4.根據事件，位元組碼查詢訂閱者
subscriptionFound |= postSingleEventForEventType(event, postingState, clazz);
}
} else {
subscriptionFound = postSingleEventForEventType(event, postingState, eventClass);
}
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));
}
}
}
postSingleEventForEventType
:
private boolean postSingleEventForEventType(Object event, PostingThreadState postingState, Class<?> eventClass) {
CopyOnWriteArrayList<Subscription> subscriptions;
synchronized (this) {
- 1.根據位元組碼取出subscriptions,還記得我們之前在subscribe這個方法的時候，
把subscrber,subscriberMethod 封裝成一個subscription 物件。
subscriptions = subscriptionsByEventType.get(eventClass);
}
if (subscriptions != null && !subscriptions.isEmpty()) {
for (Subscription subscription : subscriptions) {
- 2. 取出每一個subscription 物件
postingState.event = event;
postingState.subscription = subscription;
boolean aborted = false;
try {
- 3. post到相應的執行緒中回撥
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;
}
postToSubscription
: 根據定義的不同執行緒，呼叫相應的方法
private void postToSubscription(Subscription subscription, Object event, boolean isMainThread) {
switch (subscription.subscriberMethod.threadMode) {
case POSTING://一般沒定義的，這個就是post在哪個執行緒，響應就在哪個執行緒執行
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);
}
}
invokeSubscriber
:
void invokeSubscriber(Subscription subscription, Object event) {
try {
- 反射拿到位元組碼clazz 反射呼叫方法，就收到訊息了
subscription.subscriberMethod.method.invoke(subscription.subscriber, event);
} catch (InvocationTargetException e) {
handleSubscriberException(subscription, event, e.getCause());
} catch (IllegalAccessException e) {
throw new IllegalStateException("Unexpected exception", e);
}
}
end.