1、eventbus的使用
在activity的oncreate和ondestroy中注册和解除注册,在需要接收数据处理的方法上使用@subscribe注解,在发送数据出使用post。eventbus相比android内部广播优势在于,使用起来十分简洁,不需要像广播那种的注册,可携带数据量也比广播要多,广播仅可携带string、int等简单类型数据参数,eventbus可传递实体类,列表等数据。
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
EventBus.getDefault().register(this);
setContentView(R.layout.activity_main);
...
}
@Subscribe(threadMode = ThreadMode.MAIN)
public void getData(List<MeiLv> list) {
......
}
@Override
protected void onDestroy() {
EventBus.getDefault().unregister(this);
super.onDestroy();
}
//发送数据到观察者
EventBus.getDefault().post(object);
2、原理:
几个重要变量:
//初始化eventbus时候使用,初始化了一批判断条件参数
private static final EventBusBuilder DEFAULT_BUILDER = new EventBusBuilder();
//事件类型缓存列表
private static final Map<Class<?>, List<Class<?>>> eventTypesCache = new HashMap<>();
//用来保存注册的观察者列表
private final Map<Class<?>, CopyOnWriteArrayList<Subscription>> subscriptionsByEventType
//解析观察者的主要功能类
private final SubscriberMethodFinder subscriberMethodFinder;
//描述观察者方法
SubscriberMethod:
final Method method;//方法名
final ThreadMode threadMode;//线程类型,是后台线程还是UI线程
final Class<?> eventType;//事件类型,也就是用于接收的参数类型
final int priority;//优先级
final boolean sticky;//是否注册就就马上发送一次消息
/** Used for efficient comparison */
String methodString;
注册流程如下:
public void register(Object subscriber) {
Class<?> subscriberClass = subscriber.getClass();
//解析类中带有的@subscribe的方法
List<SubscriberMethod> subscriberMethods = subscriberMethodFinder.findSubscriberMethods(subscriberClass);
synchronized (this) {
for (SubscriberMethod subscriberMethod : subscriberMethods) {
subscribe(subscriber, subscriberMethod);
}
}
}
private void subscribe(Object subscriber, SubscriberMethod subscriberMethod) {
Class<?> eventType = subscriberMethod.eventType;
Subscription newSubscription = new Subscription(subscriber, subscriberMethod);
CopyOnWriteArrayList<Subscription> subscriptions = subscriptionsByEventType.get(eventType);
//如果当前subscriptionsByEventType中没有包含该事件类型,就将其添加到该列表中,如果已经有了,则检查当前观察者是否已经添加在该事件类型的观察者列表中了,如果已经在了,则抛出异常,这样注册类中带有@subscribe注解的方法就都添加到了不同事件类型所对应的观察者列表中了
if (subscriptions == null) {
subscriptions = new CopyOnWriteArrayList<>();
subscriptionsByEventType.put(eventType, subscriptions);
} else {
if (subscriptions.contains(newSubscription)) {
throw new EventBusException("Subscriber " + subscriber.getClass() + " already registered to event "
+ eventType);
}
}
//按照优先级将新的观察者添加到该事件类型的列表中
int size = subscriptions.size();
for (int i = 0; i <= size; i++) {
if (i == size || subscriberMethod.priority > subscriptions.get(i).subscriberMethod.priority) {
subscriptions.add(i, newSubscription);
break;
}
}
List<Class<?>> subscribedEvents = typesBySubscriber.get(subscriber);
if (subscribedEvents == null) {
subscribedEvents = new ArrayList<>();
typesBySubscriber.put(subscriber, subscribedEvents);
}
subscribedEvents.add(eventType);
//如果该subscribemethos包含粘性属性,则继续发送事件通知观察者。
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();
checkPostStickyEventToSubscription(newSubscription, stickyEvent);
}
}
} else {
Object stickyEvent = stickyEvents.get(eventType);
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.
postToSubscription(newSubscription, stickyEvent, isMainThread());
}
}
void invokeSubscriber(Subscription subscription, Object event) {
//反射调用观察者method
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);
}
}
注册流程:将类中带有@subscribe注解的方法分别添加到eventbus中的subscriptionsByEventType列表中,subscriptionsByEventType是按照事件类型来分类,也就是该方法的参数。
事件发送流程:
通过PostingThreadState来控制发送事件同步,首先将其加入到队列中eventQueue,如果当前正在发送则直接返回,正在发送的操作会将队列中的数据全部发送,发送操作主要是根据事件类型,将subscriptionsByEventType中保存的对应事件类型下的观察者列表中的所有观察者获取出来,之后反射该method方法。
public void post(Object event) {
PostingThreadState postingState = currentPostingThreadState.get();
List<Object> eventQueue = postingState.eventQueue;
eventQueue.add(event);
if (!postingState.isPosting) {
postingState.isMainThread = isMainThread();
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;
}
}
}
private void postSingleEvent(Object event, PostingThreadState postingState) throws Error {
Class<?> eventClass = event.getClass();
boolean subscriptionFound = false;
if (eventInheritance) {
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 {
subscriptionFound = postSingleEventForEventType(event, postingState, eventClass);
}
if (!subscriptionFound) {
if (logNoSubscriberMessages) {
logger.log(Level.FINE, "No subscribers registered for event " + eventClass);
}
if (sendNoSubscriberEvent && eventClass != NoSubscriberEvent.class &&
eventClass != SubscriberExceptionEvent.class) {
post(new NoSubscriberEvent(this, event));
}
}
}
private boolean postSingleEventForEventType(Object event, PostingThreadState postingState, Class<?> eventClass) {
CopyOnWriteArrayList<Subscription> subscriptions;
synchronized (this) {
//根据事件类型从之前注册时候添加的列表:subscriptionsByEventType中将该事件类型的所有观察者获取到列表中
subscriptions = subscriptionsByEventType.get(eventClass);
}
if (subscriptions != null && !subscriptions.isEmpty()) {
//轮询观察者列表中的观察者,依次发送数据
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 POSTING:
invokeSubscriber(subscription, event);
break;
case MAIN:
if (isMainThread) {
invokeSubscriber(subscription, event);
} else {
mainThreadPoster.enqueue(subscription, event);
}
break;
case MAIN_ORDERED:
if (mainThreadPoster != null) {
mainThreadPoster.enqueue(subscription, event);
} else {
// temporary: technically not correct as poster not decoupled from subscriber
invokeSubscriber(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);
}
}
void invokeSubscriber(Subscription subscription, Object event) {
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);
}
}
解除注册:
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 {
logger.log(Level.WARNING, "Subscriber to unregister was not registered before: " + subscriber.getClass());
}
}
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--;
}
}
}
}