一、 EventBus 註冊
1、EventBus.getDefault()
通過DoubleCheck創建EventBus實例
public static EventBus getDefault() {
if (defaultInstance == null) {
synchronized (EventBus.class) {
if (defaultInstance == null) {
defaultInstance = new EventBus();
}
}
}
return defaultInstance;
}
2、register(Object subscriber)
public void register(Object subscriber) {
// 獲取註冊的對象class文件
Class<?> subscriberClass = subscriber.getClass();
// 通過class查詢訂閱方法
List<SubscriberMethod> subscriberMethods = subscriberMethodFinder.findSubscriberMethods(subscriberClass);
// 遍歷訂閱方法集合
// 同步代碼塊，防止發生併發問題
synchronized (this) {
for (SubscriberMethod subscriberMethod : subscriberMethods) {
// 見下面代碼分析
subscribe(subscriber, subscriberMethod);
}
}
}
3、findSubscriberMethods
List<SubscriberMethod> findSubscriberMethods(Class<?> subscriberClass) {
// 通過查找緩存獲取訂閱方法集合
List<SubscriberMethod> subscriberMethods = METHOD_CACHE.get(subscriberClass);
if (subscriberMethods != null) {
return subscriberMethods;
}
if (ignoreGeneratedIndex) {
// 通過反射方式獲取
subscriberMethods = findUsingReflection(subscriberClass);
} else {
// 通過查詢信息獲取
subscriberMethods = findUsingInfo(subscriberClass);
}
if (subscriberMethods.isEmpty()) {
throw new EventBusException("Subscriber " + subscriberClass
+ " and its super classes have no public methods with the @Subscribe annotation");
} else {
// 添加緩存
METHOD_CACHE.put(subscriberClass, subscriberMethods);
return subscriberMethods;
}
}
4、findUsingReflection(subscriberClass)
private List<SubscriberMethod> findUsingReflection(Class<?> subscriberClass) {
FindState findState = prepareFindState();
findState.initForSubscriber(subscriberClass);
while (findState.clazz != null) {
// 關鍵查詢方法
findUsingReflectionInSingleClass(findState);
findState.moveToSuperclass();
}
return getMethodsAndRelease(findState);
}
// 通過反射獲取訂閱方法
private void findUsingReflectionInSingleClass(FindState findState) {
Method[] methods;
try {
// This is faster than getMethods, especially when subscribers are fat classes like Activities
// 獲取所有方法
methods = findState.clazz.getDeclaredMethods();
} catch (Throwable th) {
// Workaround for java.lang.NoClassDefFoundError, see https://github.com/greenrobot/EventBus/issues/149
methods = findState.clazz.getMethods();
findState.skipSuperClasses = true;
}
// 遍歷
for (Method method : methods) {
// 獲取方法修飾符
int modifiers = method.getModifiers();
// 獲取public方法
if ((modifiers & Modifier.PUBLIC) != 0 && (modifiers & MODIFIERS_IGNORE) == 0) {
Class<?>[] parameterTypes = method.getParameterTypes();
if (parameterTypes.length == 1) {
// 獲取註解
Subscribe subscribeAnnotation = method.getAnnotation(Subscribe.class);
if (subscribeAnnotation != null) {
Class<?> eventType = parameterTypes[0];
if (findState.checkAdd(method, eventType)) {
ThreadMode threadMode = subscribeAnnotation.threadMode();
// 將方法、事件類型、線程模式、優先級、粘性事件標識存入findState中
findState.subscriberMethods.add(new SubscriberMethod(method, eventType, threadMode,
subscribeAnnotation.priority(), subscribeAnnotation.sticky()));
}
}
} else if (strictMethodVerification && method.isAnnotationPresent(Subscribe.class)) {
String methodName = method.getDeclaringClass().getName() + "." + method.getName();
throw new EventBusException("@Subscribe method " + methodName +
"must have exactly 1 parameter but has " + parameterTypes.length);
}
} else if (strictMethodVerification && method.isAnnotationPresent(Subscribe.class)) {
String methodName = method.getDeclaringClass().getName() + "." + method.getName();
throw new EventBusException(methodName +
" is a illegal @Subscribe method: must be public, non-static, and non-abstract");
}
}
}
// getMethodsAndRelease(findState)
private List<SubscriberMethod> getMethodsAndRelease(FindState findState) {
List<SubscriberMethod> subscriberMethods = new ArrayList<>(findState.subscriberMethods);
// 使用完回收內存
findState.recycle();
synchronized (FIND_STATE_POOL) {
for (int i = 0; i < POOL_SIZE; i++) {
if (FIND_STATE_POOL[i] == null) {
FIND_STATE_POOL[i] = findState;
break;
}
}
}
// 返回訂閱方法
return subscriberMethods;
}
5、findUsingInfo(subscriberClass)
private List<SubscriberMethod> findUsingInfo(Class<?> subscriberClass) {
FindState findState = prepareFindState();
findState.initForSubscriber(subscriberClass);
while (findState.clazz != null) {
// 對subscriberInfo進行賦值
findState.subscriberInfo = getSubscriberInfo(findState);
if (findState.subscriberInfo != null) {
SubscriberMethod[] array = findState.subscriberInfo.getSubscriberMethods();
for (SubscriberMethod subscriberMethod : array) {
// 防止重複添加
if (findState.checkAdd(subscriberMethod.method, subscriberMethod.eventType)) {
// 添加數據到subscriberMethods中
findState.subscriberMethods.add(subscriberMethod);
}
}
} else {
// 如果沒查詢到再次通過反射獲取 ，通過反射獲取前面已經分析，不再贅述
findUsingReflectionInSingleClass(findState);
}
findState.moveToSuperclass();
}
return getMethodsAndRelease(findState);
}
6、 subscribe(subscriber, subscriberMethod);
// Must be called in synchronized block
private void subscribe(Object subscriber, SubscriberMethod subscriberMethod) {
// 獲取訂閱事件類型
Class<?> eventType = subscriberMethod.eventType;
// 將訂閱對象及訂閱類型封裝到Subscription中
Subscription newSubscription = new Subscription(subscriber, subscriberMethod);
// 通過eventType獲取訂閱集合
CopyOnWriteArrayList<Subscription> subscriptions = subscriptionsByEventType.get(eventType);
// 訂閱集合爲空
if (subscriptions == null) {
// 創建集合並將eventType作爲鍵存儲
subscriptions = new CopyOnWriteArrayList<>();
subscriptionsByEventType.put(eventType, subscriptions);
} else {
// 不允許註冊重複訂閱
if (subscriptions.contains(newSubscription)) {
throw new EventBusException("Subscriber " + subscriber.getClass() + " already registered to event "
+ eventType);
}
}
int size = subscriptions.size();
for (int i = 0; i <= size; i++) {
// 根據訂閱方法的優先級排序
if (i == size || subscriberMethod.priority > subscriptions.get(i).subscriberMethod.priority) {
subscriptions.add(i, newSubscription);
break;
}
}
// 通過subscriber獲取訂閱事件集合
List<Class<?>> subscribedEvents = typesBySubscriber.get(subscriber);
if (subscribedEvents == null) {
subscribedEvents = new ArrayList<>();
// 將訂閱事件集合和subscriber通過map生成映射關係
typesBySubscriber.put(subscriber, subscribedEvents);
}
subscribedEvents.add(eventType);
// 粘性事件處理
if (subscriberMethod.sticky) {
if (eventInheritance) {
// Existing sticky events of all subclasses of eventType have to be considered.
// Note: Iterating over all events may be inefficient with lots of sticky events,
// thus data structure should be changed to allow a more efficient lookup
// (e.g. an additional map storing sub classes of super classes: Class -> List<Class>).
Set<Map.Entry<Class<?>, Object>> entries = stickyEvents.entrySet();
for (Map.Entry<Class<?>, Object> entry : entries) {
Class<?> candidateEventType = entry.getKey();
if (eventType.isAssignableFrom(candidateEventType)) {
Object stickyEvent = entry.getValue();
// 發送粘性事件通知
checkPostStickyEventToSubscription(newSubscription, stickyEvent);
}
}
} else {
Object stickyEvent = stickyEvents.get(eventType);
checkPostStickyEventToSubscription(newSubscription, stickyEvent);
}
}
}
7、checkPostStickyEventToSubscription(newSubscription, stickyEvent);
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.
// 發送到訂閱者
postToSubscription(newSubscription, stickyEvent, Looper.getMainLooper() == Looper.myLooper());
}
}
二、 EventBus 反註冊
/** 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);
}
// 移除訂閱者
typesBySubscriber.remove(subscriber);
} else {
Log.w(TAG, "Subscriber to unregister was not registered before: " + subscriber.getClass());
}
}
// 將註冊事件移除
/** 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--;
}
}
}
}
反註冊很簡單，只是將註冊事件及訂閱者移除，防止重複發送及接收事件
三、 EventBus 發送數據
1、post(Object event)
/** Posts the given event to the event bus. */
public void post(Object event) {
// 獲取當前發送數據線程狀態
PostingThreadState postingState = currentPostingThreadState.get();
List<Object> eventQueue = postingState.eventQueue;
// 將需要發送的事件放入隊列中
eventQueue.add(event);
// 非posting狀態，防止多個重複發送事件
if (!postingState.isPosting) {
// 判斷是否在主線程中
postingState.isMainThread = Looper.getMainLooper() == Looper.myLooper();
postingState.isPosting = true;
if (postingState.canceled) {
throw new EventBusException("Internal error. Abort state was not reset");
}
try {
// 循環發佈數據
while (!eventQueue.isEmpty()) {
postSingleEvent(eventQueue.remove(0), postingState);
}
} finally {
// 重新置位
postingState.isPosting = false;
postingState.isMainThread = false;
}
}
}
2、 postSingleEvent 發佈單個事件
private void postSingleEvent(Object event, PostingThreadState postingState) throws Error {
Class<?> eventClass = event.getClass();
boolean subscriptionFound = false;
// 是否存在事件繼承關係
if (eventInheritance) {
// 通過class獲取所有事件類型
List<Class<?>> eventTypes = lookupAllEventTypes(eventClass);
int countTypes = eventTypes.size();
for (int h = 0; h < countTypes; h++) {
Class<?> clazz = eventTypes.get(h);
subscriptionFound |= postSingleEventForEventType(event, postingState, clazz);
}
} else {
// 直接發佈事件
subscriptionFound = postSingleEventForEventType(event, postingState, eventClass);
}
// 未發現訂閱方法，拋出異常
if (!subscriptionFound) {
if (logNoSubscriberMessages) {
Log.d(TAG, "No subscribers registered for event " + eventClass);
}
if (sendNoSubscriberEvent && eventClass != NoSubscriberEvent.class &&
eventClass != SubscriberExceptionEvent.class) {
// 發佈未發現事件通知
post(new NoSubscriberEvent(this, event));
}
}
}
3、postSingleEventForEventType 通過事件類型發佈獨立事件
private boolean postSingleEventForEventType(Object event, PostingThreadState postingState, Class<?> eventClass) {
CopyOnWriteArrayList<Subscription> subscriptions;
// 獲取訂閱者集合
synchronized (this) {
subscriptions = subscriptionsByEventType.get(eventClass);
}
if (subscriptions != null && !subscriptions.isEmpty()) {
// 通過循環遍歷發佈事件
for (Subscription subscription : subscriptions) {
postingState.event = event;
postingState.subscription = subscription;
boolean aborted = false;
try {
// 向訂閱者發佈事件
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;
}
4、postToSubscription
private void postToSubscription(Subscription subscription, Object event, boolean isMainThread) {
// 通過ThreadMode執行不同的發送策略
switch (subscription.subscriberMethod.threadMode) {
case POSTING:
// 查看5
invokeSubscriber(subscription, event);
break;
case MAIN:
if (isMainThread) {
invokeSubscriber(subscription, event);
} else {
// 指定mode爲MAIN時如果不在主線程執行策略2
// 查看6
mainThreadPoster.enqueue(subscription, event);
}
break;
case BACKGROUND:
if (isMainThread) {
// 指定BACKGROUND模式時，主線程處理
// 查看7
backgroundPoster.enqueue(subscription, event);
} else {
invokeSubscriber(subscription, event);
}
break;
case ASYNC:
// 與查看7源碼相同
asyncPoster.enqueue(subscription, event);
break;
default:
throw new IllegalStateException("Unknown thread mode: " + subscription.subscriberMethod.threadMode);
}
}
5、invokeSubscriber
void invokeSubscriber(Subscription subscription, Object event) {
try {
// 通過反射調用訂閱者接收事件
subscription.subscriberMethod.method.invoke(subscription.subscriber, event);
} catch (InvocationTargetException e) {
handleSubscriberException(subscription, event, e.getCause());
} catch (IllegalAccessException e) {
throw new IllegalStateException("Unexpected exception", e);
}
}
6、mainThreadPoster.enqueue(subscription, event);
void enqueue(Subscription subscription, Object event) {
PendingPost pendingPost = PendingPost.obtainPendingPost(subscription, event);
synchronized (this) {
queue.enqueue(pendingPost);
if (!handlerActive) {
handlerActive = true;
// 通過handler發送數據，完成線程切換
if (!sendMessage(obtainMessage())) {
throw new EventBusException("Could not send handler message");
}
}
}
}
7、enqueue
public void enqueue(Subscription subscription, Object event) {
PendingPost pendingPost = PendingPost.obtainPendingPost(subscription, event);
synchronized (this) {
queue.enqueue(pendingPost);
if (!executorRunning) {
executorRunning = true;
// 通過eventbus獲取ExecutorService()執行自己
eventBus.getExecutorService().execute(this);
}
}
}
// 通過Executor執行runnable
public interface Executor {
/**
* Executes the given command at some time in the future. The command
* may execute in a new thread, in a pooled thread, or in the calling
* thread, at the discretion of the {@code Executor} implementation.
*
* @param command the runnable task
* @throws RejectedExecutionException if this task cannot be
* accepted for execution
* @throws NullPointerException if command is null
*/
void execute(Runnable command);
}
四、EventBus 接收數據
接收數據，只需要註冊，通過在方法上添加@Subscribe註解即可成爲接收者，基本操作，不再贅述
五、小結
EventBus通過觀察者設計模式結合Handler中生產者與消費者設計模式實現，通過註解的方式來實現事件的接收，簡化了接入使用，但是通過反射方式獲取註解效率問題需要考慮。