65.源码解析：EventBus
1.使用
注册：
public class MyBaseFragment extends Fragment {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//注册EventBus
EventBus.getDefault().register(this);
}
@Override
public void onDestroy() {
super.onDestroy();
//反注册EventBus
EventBus.getDefault().unregister(this);
}
public void onEvent(MyBaseEvent event){
//接收消息-默认类型，必须定义，不然程序会报错！！！但是没卵用
}
public void onEventMainThread(MyBaseEvent event){
//接收消息-主线程
}
public void onEventBackgroundThread(MyBaseEvent event){
//接收消息-后台线程
}
EventBus.getDefault().post(new MyBaseEvent(MyEventEnum.AddPkEnd));订阅：
@Override
public void onEventMainThread(MyBaseEvent ev) {
super.onEventMainThread(ev);
if (ev.getAction() == MyEventEnum.AddPkEnd) {
tvPkNumer.setText("" + MyConfig.pkNumber);
}
2.源码解析
（1）注册
public static EventBus getDefault() {
if(defaultInstance == null) {
Class var0 = EventBus.class;
synchronized(EventBus.class) {
if(defaultInstance == null) {
defaultInstance = new EventBus();
}
}
}
return defaultInstance;
}
public void register(Object subscriber) {
register(subscriber, false, 0);
}
private synchronized void register(Object subscriber, boolean sticky, int priority) {（2）根据订阅类，找到订阅类中的所有订阅方法（以onEvent开头的方法……）
List<SubscriberMethod> subscriberMethods = subscriberMethodFinder.findSubscriberMethods(subscriber.getClass());
for (SubscriberMethod subscriberMethod : subscriberMethods) {
subscribe(subscriber, subscriberMethod, sticky, priority);
}
}
List<SubscriberMethod> findSubscriberMethods(Class<?> subscriberClass) {（3）遍历订阅类中的订阅方法，存进一个全局的Map，key为eventType, value为订阅方法的包装类（持有订阅者、订阅方法（方法、线程模式、事件类型）、优先级）
String key = subscriberClass.getName();
List<SubscriberMethod> subscriberMethods;
synchronized (methodCache) {
subscriberMethods = methodCache.get(key);
}
if (subscriberMethods != null) {
return subscriberMethods;
}
subscriberMethods = new ArrayList<SubscriberMethod>();
Class<?> clazz = subscriberClass;
HashSet<String> eventTypesFound = new HashSet<String>();
StringBuilder methodKeyBuilder = new StringBuilder();
while (clazz != null) {
String name = clazz.getName();
if (name.startsWith("java.") || name.startsWith("javax.") || name.startsWith("android.")) {
// Skip system classes, this just degrades performance
break;
}
// Starting with EventBus 2.2 we enforced methods to be public (might change with annotations again)
Method[] methods = clazz.getDeclaredMethods();
for (Method method : methods) {
String methodName = method.getName();
if (methodName.startsWith(ON_EVENT_METHOD_NAME)) {
int modifiers = method.getModifiers();
if ((modifiers & Modifier.PUBLIC) != 0 && (modifiers & MODIFIERS_IGNORE) == 0) {
Class<?>[] parameterTypes = method.getParameterTypes();
if (parameterTypes.length == 1) {
String modifierString = methodName.substring(ON_EVENT_METHOD_NAME.length());
ThreadMode threadMode;
if (modifierString.length() == 0) {
threadMode = ThreadMode.PostThread;
} else if (modifierString.equals("MainThread")) {
threadMode = ThreadMode.MainThread;
} else if (modifierString.equals("BackgroundThread")) {
threadMode = ThreadMode.BackgroundThread;
} else if (modifierString.equals("Async")) {
threadMode = ThreadMode.Async;
} else {
if (skipMethodVerificationForClasses.containsKey(clazz)) {
continue;
} else {
throw new EventBusException("Illegal onEvent method, check for typos: " + method);
}
}
Class<?> eventType = parameterTypes[0];
methodKeyBuilder.setLength(0);
methodKeyBuilder.append(methodName);
methodKeyBuilder.append('>').append(eventType.getName());
String methodKey = methodKeyBuilder.toString();
if (eventTypesFound.add(methodKey)) {
// Only add if not already found in a sub class
subscriberMethods.add(new SubscriberMethod(method, threadMode, eventType));
}
}
} else if (!skipMethodVerificationForClasses.containsKey(clazz)) {
Log.d(EventBus.TAG, "Skipping method (not public, static or abstract): " + clazz + "."
+ methodName);
}
}
}
clazz = clazz.getSuperclass();
}
if (subscriberMethods.isEmpty()) {
throw new EventBusException("Subscriber " + subscriberClass + " has no public methods called "
+ ON_EVENT_METHOD_NAME);
} else {
synchronized (methodCache) {
methodCache.put(key, subscriberMethods);
}
return subscriberMethods;
}
}
这里：Value类型为CopyOnWriteArrayList，为线程安全的类ArrayList（不是继承自ArrayList）
private void subscribe(Object subscriber, SubscriberMethod subscriberMethod, boolean sticky, int priority) {
Class<?> eventType = subscriberMethod.eventType;
CopyOnWriteArrayList<Subscription> subscriptions = subscriptionsByEventType.get(eventType);
Subscription newSubscription = new Subscription(subscriber, subscriberMethod, priority);
if (subscriptions == null) {
subscriptions = new CopyOnWriteArrayList<Subscription>();
subscriptionsByEventType.put(eventType, subscriptions);
} else {
if (subscriptions.contains(newSubscription)) {
throw new EventBusException("Subscriber " + subscriber.getClass() + " already registered to event "
+ eventType);
}
}
// Starting with EventBus 2.2 we enforced methods to be public (might change with annotations again)
// subscriberMethod.method.setAccessible(true);
int size = subscriptions.size();
for (int i = 0; i <= size; i++) {
if (i == size || newSubscription.priority > subscriptions.get(i).priority) {
subscriptions.add(i, newSubscription);
break;
}
}
List<Class<?>> subscribedEvents = typesBySubscriber.get(subscriber);
if (subscribedEvents == null) {
subscribedEvents = new ArrayList<Class<?>>();
typesBySubscriber.put(subscriber, subscribedEvents);
}
subscribedEvents.add(eventType);
if (sticky) {
Object stickyEvent;
synchronized (stickyEvents) {
stickyEvent = stickyEvents.get(eventType);
}
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, Looper.getMainLooper() == Looper.myLooper());
}
}
}
（4）发布事件，使用ThreadLocal,为每个线程分别获取一个事件发布状态的副本，遍历事件队列，循环发布事件
这里：isMainThread存储了当前是否是主线程，后面会用到
public void post(Object event) {
EventBus.PostingThreadState postingState = (EventBus.PostingThreadState)this.currentPostingThreadState.get();
List 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()) {
this.postSingleEvent(eventQueue.remove(0), postingState);
}
} finally {
postingState.isPosting = false;
postingState.isMainThread = false;
}
}
}
（5）遍历所有的事件类型
private void postSingleEvent(Object event, EventBus.PostingThreadState postingState) throws Error {
Class eventClass = event.getClass();
boolean subscriptionFound = false;
if(this.eventInheritance) {
List eventTypes = this.lookupAllEventTypes(eventClass);
int countTypes = eventTypes.size();
for(int h = 0; h < countTypes; ++h) {
Class clazz = (Class)eventTypes.get(h);
subscriptionFound |= this.postSingleEventForEventType(event, postingState, clazz);
}
} else {
subscriptionFound = this.postSingleEventForEventType(event, postingState, eventClass);
}
if(!subscriptionFound) {
if(this.logNoSubscriberMessages) {
Log.d(TAG, "No subscribers registered for event " + eventClass);
}
if(this.sendNoSubscriberEvent && eventClass != NoSubscriberEvent.class && eventClass != SubscriberExceptionEvent.class) {
this.post(new NoSubscriberEvent(this, event));
}
}
}
private boolean postSingleEventForEventType(Object event, PostingThreadState postingState, Class<?> eventClass) {（7）根据订阅方法的线程模式，以及当前的线程类型，分发执行订阅方法
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;
}
private void postToSubscription(Subscription subscription, Object event, boolean isMainThread) {
switch (subscription.subscriberMethod.threadMode) {
case PostThread:
invokeSubscriber(subscription, event);
break;
case MainThread:
if (isMainThread) {
invokeSubscriber(subscription, event);
} else {
mainThreadPoster.enqueue(subscription, event);
}
break;
case BackgroundThread:
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);
}
}
void invokeSubscriber(Subscription subscription, Object event) {（8-2）切换到主线程执行订阅方法，其实就是用了Handler
try {
subscription.subscriberMethod.method.invoke(subscription.subscriber, event);
} catch (InvocationTargetException e) {
handleSubscriberException(subscription, event, e.getCause());
} catch (IllegalAccessException e) {
throw new IllegalStateException("Unexpected exception", e);
}
}
void enqueue(Subscription subscription, Object event) {
PendingPost pendingPost = PendingPost.obtainPendingPost(subscription, event);
synchronized (this) {
queue.enqueue(pendingPost);
if (!handlerActive) {
handlerActive = true;
if (!sendMessage(obtainMessage())) {
throw new EventBusException("Could not send handler message");
}
}
}
}
@Override
public void handleMessage(Message msg) {
boolean rescheduled = false;
try {
long started = SystemClock.uptimeMillis();
while (true) {
PendingPost pendingPost = queue.poll();
if (pendingPost == null) {
synchronized (this) {
// Check again, this time in synchronized
pendingPost = queue.poll();
if (pendingPost == null) {
handlerActive = false;
return;
}
}
}
eventBus.invokeSubscriber(pendingPost);
long timeInMethod = SystemClock.uptimeMillis() - started;
if (timeInMethod >= maxMillisInsideHandleMessage) {
if (!sendMessage(obtainMessage())) {
throw new EventBusException("Could not send handler message");
}
rescheduled = true;
return;
}
}
} finally {
handlerActive = rescheduled;
}
}
（8-3）切换到后台线程执行订阅方法，其实就是用了Executors.newCachedThreadPool()逐个控制并发
public void enqueue(Subscription subscription, Object event) {
PendingPost pendingPost = PendingPost.obtainPendingPost(subscription, event);
synchronized (this) {
queue.enqueue(pendingPost);
if (!executorRunning) {
executorRunning = true;
eventBus.getExecutorService().execute(this);
}
}
}
@Override
public void run() {
try {
try {
while (true) {
PendingPost pendingPost = queue.poll(1000);
if (pendingPost == null) {
synchronized (this) {
// Check again, this time in synchronized
pendingPost = queue.poll();
if (pendingPost == null) {
executorRunning = false;
return;
}
}
}
eventBus.invokeSubscriber(pendingPost);
}
} catch (InterruptedException e) {
Log.w("Event", Thread.currentThread().getName() + " was interruppted", e);
}
} finally {
executorRunning = false;
}
}
（8-4）切换到异步线程执行订阅方法，其实就是用了Executors.newCachedThreadPool()动态控制并发
public void enqueue(Subscription subscription, Object event) {
PendingPost pendingPost = PendingPost.obtainPendingPost(subscription, event);
queue.enqueue(pendingPost);
eventBus.getExecutorService().execute(this);
}
@Override
public void run() {
PendingPost pendingPost = queue.poll();
if(pendingPost == null) {
throw new IllegalStateException("No pending post available");
}
eventBus.invokeSubscriber(pendingPost);
}
void invokeSubscriber(PendingPost pendingPost) {
Object event = pendingPost.event;
Subscription subscription = pendingPost.subscription;
PendingPost.releasePendingPost(pendingPost);
if (subscription.active) {
invokeSubscriber(subscription, event);
}
}
类图：
参考：
