使用
- 导入EventBus
implementation("org.greenrobot:eventbus:3.3.1")
- 定义事件
public static class MessageEvent {
/* Additional fields if needed */
}
- 注册和解注册
@Override
public void onStart() {
super.onStart();
EventBus.getDefault().register(this);
}
@Override
public void onStop() {
super.onStop();
EventBus.getDefault().unregister(this);
}
- 监听事件
@Subscribe(threadMode = ThreadMode.MAIN)
public void onMessageEvent(MessageEvent event) {
// Do something
}
- 发送事件
EventBus.getDefault().post(new MessageEvent());
核心架构
源码解析
初始化
EventBus.getDefault().register(this);
看下getDefault方法
public static EventBus getDefault() {
EventBus instance = defaultInstance;
if (instance == null) {
synchronized (EventBus.class) {
instance = EventBus.defaultInstance;
if (instance == null) {
instance = EventBus.defaultInstance = new EventBus();
}
}
}
return instance;
}
很简单，返回一个单例。
看下构造方法。
public EventBus() {
this(DEFAULT_BUILDER);
}
为什么构造方法是public的？
在我们项目中，并不是仅仅存在一条总线，也存在其它的总线。因此，我们订阅者也可以订阅到其它的总线之上，然后通过不同的EventBus发送数据。那么，我们需要注意的是，不同的EventBus发送的数据，是相互隔离开来的，订阅者只会收到注册到当前的EventBus发送的数据。
这样做的好处个人感觉有两点：
- 解耦
- 提高效率。项目大的时候索引搜索也是需要时间的。
成员变量
EventBus(EventBusBuilder builder) {
（1）日志打印
logger = builder.getLogger();
（2）eventType 为Key, 订阅者和订阅者方法封装类为Value的map。
subscriptionsByEventType = new HashMap<>();
（3）订阅者为Key，eventType为Value的map。
typesBySubscriber = new HashMap<>();
（4）粘性事件
stickyEvents = new ConcurrentHashMap<>();
（5）切换主线程
mainThreadSupport = builder.getMainThreadSupport();
（6）将事件发送到主线程的Handler。
mainThreadPoster = mainThreadSupport != null ? mainThreadSupport.createPoster(this) : null;
（7）将事件发送到子线程的，通过线程池实现。
backgroundPoster = new BackgroundPoster(this);
(8) 将事件发送到子线程的，通过线程池实现。和上面的区别看下具体实现
asyncPoster = new AsyncPoster(this);
（9）订阅者数量
indexCount = builder.subscriberInfoIndexes != null ? builder.subscriberInfoIndexes.size() : 0;
（10）@Subscribe注解方法找寻器
subscriberMethodFinder = new SubscriberMethodFinder(builder.subscriberInfoIndexes,
builder.strictMethodVerification, builder.ignoreGeneratedIndex);
（11）当调用事件处理函数时，若发生了异常是否进行异常信息打印。默认true
logSubscriberExceptions = builder.logSubscriberExceptions;
（12）当没有订阅者订阅该事件时，是否打印日志。默认true
logNoSubscriberMessages = builder.logNoSubscriberMessages;
（13）当调用事件处理函数时，若发生了异常是否发送SubscriberExceptionEvent这个事件。默认true
sendSubscriberExceptionEvent = builder.sendSubscriberExceptionEvent;
（14）当没有订阅者订阅该事件时，是否发送NoSubscriberEvent事件。默认true
sendNoSubscriberEvent = builder.sendNoSubscriberEvent;
（15）是否抛出SubscriberException异常。默认false
throwSubscriberException = builder.throwSubscriberException;
（16）与event有继承关系的是否都需要发送。默认true
eventInheritance = builder.eventInheritance;
（17）执行服务线程池
executorService = builder.executorService;
}
线程切换
mainThreadPoster
mainThreadPoster = mainThreadSupport != null ? mainThreadSupport.createPoster(this) : null;
public class DefaultAndroidMainThreadSupport implements MainThreadSupport {
@Override
public boolean isMainThread() {
return Looper.getMainLooper() == Looper.myLooper();
}
@Override
public Poster createPoster(EventBus eventBus) {
return new HandlerPoster(eventBus, Looper.getMainLooper(), 10);
}
}
重点看下HandlerPoster
public class HandlerPoster extends Handler implements Poster {
（1）PendingPost的队列
private final PendingPostQueue queue;
private final int maxMillisInsideHandleMessage;
private final EventBus eventBus;
(2) Handler是否可用
private boolean handlerActive;
public HandlerPoster(EventBus eventBus, Looper looper, int maxMillisInsideHandleMessage) {
super(looper);
this.eventBus = eventBus;
this.maxMillisInsideHandleMessage = maxMillisInsideHandleMessage;
queue = new PendingPostQueue();
}
public void enqueue(Subscription subscription, Object event) {
（2）从缓存池获取一个PendingPost
PendingPost pendingPost = PendingPost.obtainPendingPost(subscription, event);
synchronized (this) {
queue.enqueue(pendingPost);
if (!handlerActive) {
handlerActive = true;
（3）发送消息，会调用handleMessage，切换回主线程，
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();
（4）while循环从队列里面依次取出
while (true) {
PendingPost pendingPost = queue.poll();
（5）通过double check判断队列是否为空
if (pendingPost == null) {
synchronized (this) {
// Check again, this time in synchronized
pendingPost = queue.poll();
if (pendingPost == null) {
handlerActive = false;
return;
}
}
}
（6）通过反射来完成事件分发
eventBus.invokeSubscriber(pendingPost);
long timeInMethod = SystemClock.uptimeMillis() - started;
（7）事件分发时间大于最大值就返回。
if (timeInMethod >= maxMillisInsideHandleMessage) {
if (!sendMessage(obtainMessage())) {
throw new EventBusException("Could not send handler message");
}
rescheduled = true;
return;
}
}
} finally {
handlerActive = rescheduled;
}
}
}
backgroundPoster
final class BackgroundPoster implements Runnable, Poster {
private final PendingPostQueue queue;
private final EventBus eventBus;
（1）线程池是否在运行
private volatile boolean executorRunning;
BackgroundPoster(EventBus eventBus) {
this.eventBus = eventBus;
queue = new PendingPostQueue();
}
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;
}
}
}
（）通过反射执行
eventBus.invokeSubscriber(pendingPost);
}
} catch (InterruptedException e) {
eventBus.getLogger().log(Level.WARNING, Thread.currentThread().getName() + " was interruppted", e);
}
} finally {
executorRunning = false;
}
}
}
AsyncPoster
class AsyncPoster implements Runnable, Poster {
private final PendingPostQueue queue;
private final EventBus eventBus;
AsyncPoster(EventBus eventBus) {
this.eventBus = eventBus;
queue = new PendingPostQueue();
}
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);
}
}
共同点：
- 都是通过反射完成事件分发。
不同点：
-
HandlerPoster 通过Handle把任务切换到主线程，backgroundPoster AsyncPoster 通过线程池切换到子线程。
-
HandlerPoster，backgroundPoster 会一次把队列里面的都执行完，AsyncPoster一次只执行一个，适合执行耗时比较长的任务。
特别注意
- HandlerPoster 每次执行事件分发都会判断时间是否大于最大值。大于就返回，重新开始。
Subscribe注解
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.METHOD})
public @interface Subscribe {
（1）线程模式，对应mainThreadPoster、backgroundPoster、asyncPoster这三个Poster
ThreadMode threadMode() default ThreadMode.POSTING;
/**
* If true, delivers the most recent sticky event (posted with
* {@link EventBus#postSticky(Object)}) to this subscriber (if event available).
*/
（2）是否是粘性事件
boolean sticky() default false;
/** Subscriber priority to influence the order of event delivery.
* Within the same delivery thread ({@link ThreadMode}), higher priority subscribers will receive events before
* others with a lower priority. The default priority is 0. Note: the priority does *NOT* affect the order of
* delivery among subscribers with different {@link ThreadMode}s! */
（3）优先级，优先级高的先收到
int priority() default 0;
}
看下ThreadMode
public enum ThreadMode {
/**
* Subscriber will be called directly in the same thread, which is posting the event. This is the default. Event delivery
* implies the least overhead because it avoids thread switching completely. Thus this is the recommended mode for
* simple tasks that are known to complete in a very short time without requiring the main thread. Event handlers
* using this mode must return quickly to avoid blocking the posting thread, which may be the main thread.
*/
（1）当前线程
POSTING,
/**
* On Android, subscriber will be called in Android's main thread (UI thread). If the posting thread is
* the main thread, subscriber methods will be called directly, blocking the posting thread. Otherwise the event
* is queued for delivery (non-blocking). Subscribers using this mode must return quickly to avoid blocking the main thread.
* If not on Android, behaves the same as {@link #POSTING}.
*/
（2）主线程
MAIN,
/**
* On Android, subscriber will be called in Android's main thread (UI thread). Different from {@link #MAIN},
* the event will always be queued for delivery. This ensures that the post call is non-blocking.
*/
（3）主线程按照顺序
MAIN_ORDERED,
/**
* On Android, subscriber will be called in a background thread. If posting thread is not the main thread, subscriber methods
* will be called directly in the posting thread. If the posting thread is the main thread, EventBus uses a single
* background thread, that will deliver all its events sequentially. Subscribers using this mode should try to
* return quickly to avoid blocking the background thread. If not on Android, always uses a background thread.
*/
（4）子线程
BACKGROUND,
/**
* Subscriber will be called in a separate thread. This is always independent from the posting thread and the
* main thread. Posting events never wait for subscriber methods using this mode. Subscriber methods should
* use this mode if their execution might take some time, e.g. for network access. Avoid triggering a large number
* of long running asynchronous subscriber methods at the same time to limit the number of concurrent threads. EventBus
* uses a thread pool to efficiently reuse threads from completed asynchronous subscriber notifications.
*/
（5）单独子线程
ASYNC
}
还是比较简单的。
可以参照使用看下。
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);
}
}
注册
public void register(Object subscriber) {
if (AndroidDependenciesDetector.isAndroidSDKAvailable() && !AndroidDependenciesDetector.areAndroidComponentsAvailable()) {
// Crash if the user (developer) has not imported the Android compatibility library.
throw new RuntimeException("It looks like you are using EventBus on Android, " +
"make sure to add the "eventbus" Android library to your dependencies.");
}
（1）获取订阅者的Class对象
Class<?> subscriberClass = subscriber.getClass();
（2）找到当前订阅者的所有订阅方法
List<SubscriberMethod> subscriberMethods = subscriberMethodFinder.findSubscriberMethods(subscriberClass);
synchronized (this) {
for (SubscriberMethod subscriberMethod : subscriberMethods) {
subscribe(subscriber, subscriberMethod);
}
}
}
看下SubscriberMethod对象。
public class SubscriberMethod {
（1）订阅的方法
final Method method;
（2）订阅的模式
final ThreadMode threadMode;
（3）事件类型
final Class<?> eventType;
（4）优先级
final int priority;
（5）是否是粘性事件
final boolean sticky;
/** Used for efficient comparison */
（6）判断是否是同一个方法，
String methodString;
看下SubscriberMethodFinder成员变量。
class SubscriberMethodFinder {
/*
* In newer class files, compilers may add methods. Those are called bridge or synthetic methods.
* EventBus must ignore both. There modifiers are not public but defined in the Java class file format:
* http://docs.oracle.com/javase/specs/jvms/se7/html/jvms-4.html#jvms-4.6-200-A.1
*/
private static final int BRIDGE = 0x40;
private static final int SYNTHETIC = 0x1000;
private static final int MODIFIERS_IGNORE = Modifier.ABSTRACT | Modifier.STATIC | BRIDGE | SYNTHETIC;
（1）通过ConcurrentHashMap存储订阅类里面的所有订阅方法
private static final Map<Class<?>, List<SubscriberMethod>> METHOD_CACHE = new ConcurrentHashMap<>();
（2）订阅的索引
private List<SubscriberInfoIndex> subscriberInfoIndexes;
private final boolean strictMethodVerification;
private final boolean ignoreGeneratedIndex;
private static final int POOL_SIZE = 4;
private static final FindState[] FIND_STATE_POOL = new FindState[POOL_SIZE];
}
看下findSubscriberMethods方法。
List<SubscriberMethod> findSubscriberMethods(Class<?> subscriberClass) {
（1）先从缓存里面找到这个类的所有订阅方法，找到就直接返回
List<SubscriberMethod> subscriberMethods = METHOD_CACHE.get(subscriberClass);
if (subscriberMethods != null) {
return subscriberMethods;
}
if (ignoreGeneratedIndex) {
（2）通过反射查找
subscriberMethods = findUsingReflection(subscriberClass);
} else {
（3）通过APT查找
subscriberMethods = findUsingInfo(subscriberClass);
}
if (subscriberMethods.isEmpty()) {
throw new EventBusException("Subscriber " + subscriberClass
+ " and its super classes have no public methods with the @Subscribe annotation");
} else {
（3）找到的方法放到缓存
METHOD_CACHE.put(subscriberClass, subscriberMethods);
return subscriberMethods;
}
}
看下findUsingReflectionInSingleClass方法
private void findUsingReflectionInSingleClass(FindState findState) {
Method[] methods;
try {
// This is faster than getMethods, especially when subscribers are fat classes like Activities
（1）获取所有声明的方法
methods = findState.clazz.getDeclaredMethods();
} catch (Throwable th) {
// Workaround for java.lang.NoClassDefFoundError, see https://github.com/greenrobot/EventBus/issues/149
try {
（2）获取单签类的public方法，不包括父类
methods = findState.clazz.getMethods();
} catch (LinkageError error) { // super class of NoClassDefFoundError to be a bit more broad...
String msg = "Could not inspect methods of " + findState.clazz.getName();
if (ignoreGeneratedIndex) {
msg += ". Please consider using EventBus annotation processor to avoid reflection.";
} else {
msg += ". Please make this class visible to EventBus annotation processor to avoid reflection.";
}
throw new EventBusException(msg, error);
}
findState.skipSuperClasses = true;
}
（3）循环遍历
for (Method method : methods) {
（4）获取方法修饰符
int modifiers = method.getModifiers();
（5）如果是public类型，但非abstract、static等
if ((modifiers & Modifier.PUBLIC) != 0 && (modifiers & MODIFIERS_IGNORE) == 0) {
（6）获得当前方法所有参数的类型
Class<?>[] parameterTypes = method.getParameterTypes();
（7）参数长度是1，因为Eventbus订阅只允许是1
if (parameterTypes.length == 1) {
（8）获取订阅方法的注解
Subscribe subscribeAnnotation = method.getAnnotation(Subscribe.class);
if (subscribeAnnotation != null) {
Class<?> eventType = parameterTypes[0];
if (findState.checkAdd(method, eventType)) {
ThreadMode threadMode = subscribeAnnotation.threadMode();
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");
}
}
}
看下findUsingInfo方法。
private List<SubscriberMethod> findUsingInfo(Class<?> subscriberClass) {
（1）看下FindState，通过缓存池找到，找不到New一个。
FindState findState = prepareFindState();
（2）初始化订阅者Class对象
findState.initForSubscriber(subscriberClass);
while (findState.clazz != null) {
（3）获取subscriberInfo, 默认为null，实际会在Subscriber索引里面查找。
findState.subscriberInfo = getSubscriberInfo(findState);
if (findState.subscriberInfo != null) {
（4）获取订阅者所有方法
SubscriberMethod[] array = findState.subscriberInfo.getSubscriberMethods();
for (SubscriberMethod subscriberMethod : array) {
if (findState.checkAdd(subscriberMethod.method, subscriberMethod.eventType)) {
findState.subscriberMethods.add(subscriberMethod);
}
}
} else {
（5）通过反射查找
findUsingReflectionInSingleClass(findState);
}
（6）查找父类的
findState.moveToSuperclass();
}
（7）返回找到的方法，并回收findState
return getMethodsAndRelease(findState);
}
看下 FindState ，重点关注下 checkAdd 方法。
static class FindState {
（1）订阅方法
final List<SubscriberMethod> subscriberMethods = new ArrayList<>();
（2）订阅事件为Key，订阅方法为Value。
final Map<Class, Object> anyMethodByEventType = new HashMap<>();
（3）订阅方法为Key，订阅类的Class对象为Value。
final Map<String, Class> subscriberClassByMethodKey = new HashMap<>();
final StringBuilder methodKeyBuilder = new StringBuilder(128);
Class<?> subscriberClass;
Class<?> clazz;
boolean skipSuperClasses;
SubscriberInfo subscriberInfo;
void initForSubscriber(Class<?> subscriberClass) {
this.subscriberClass = clazz = subscriberClass;
skipSuperClasses = false;
subscriberInfo = null;
}
void recycle() {
subscriberMethods.clear();
anyMethodByEventType.clear();
subscriberClassByMethodKey.clear();
methodKeyBuilder.setLength(0);
subscriberClass = null;
clazz = null;
skipSuperClasses = false;
subscriberInfo = null;
}
（4）判断订阅方法是否添加到集合当中
boolean checkAdd(Method method, Class<?> eventType) {
// 2 level check: 1st level with event type only (fast), 2nd level with complete signature when required.
// Usually a subscriber doesn't have methods listening to the same event type.
(5) 判断父类是否有订阅这个事件。
Object existing = anyMethodByEventType.put(eventType, method);
if (existing == null) {
return true;
} else {
if (existing instanceof Method) {
if (!checkAddWithMethodSignature((Method) existing, eventType)) {
// Paranoia check
throw new IllegalStateException();
}
// Put any non-Method object to "consume" the existing Method
anyMethodByEventType.put(eventType, this);
}
return checkAddWithMethodSignature(method, eventType);
}
}
(5) 判断是否子类订阅了
private boolean checkAddWithMethodSignature(Method method, Class<?> eventType) {
methodKeyBuilder.setLength(0);
methodKeyBuilder.append(method.getName());
methodKeyBuilder.append('>').append(eventType.getName());
String methodKey = methodKeyBuilder.toString();
Class<?> methodClass = method.getDeclaringClass();
Class<?> methodClassOld = subscriberClassByMethodKey.put(methodKey, methodClass);
if (methodClassOld == null || methodClassOld.isAssignableFrom(methodClass)) {
// Only add if not already found in a sub class
return true;
} else {
// Revert the put, old class is further down the class hierarchy
subscriberClassByMethodKey.put(methodKey, methodClassOld);
return false;
}
}
void moveToSuperclass() {
if (skipSuperClasses) {
clazz = null;
} else {
clazz = clazz.getSuperclass();
String clazzName = clazz.getName();
// Skip system classes, this degrades performance.
// Also we might avoid some ClassNotFoundException (see FAQ for background).
if (clazzName.startsWith("java.") || clazzName.startsWith("javax.") ||
clazzName.startsWith("android.") || clazzName.startsWith("androidx.")) {
clazz = null;
}
}
}
}
checkAdd这个方法主要两件事
-
判断方法FindState的anyMethodByEventType map是否已经添加过以当前eventType为key的键值对。
-
如果添加判断是否是子类添加的。
注册总结：
- 获取当前订阅者的Class对象。
- 通过反射或者通过索引找到当前对象的所有订阅方法。
- 每个方法一次遍历订阅。
订阅
// Must be called in synchronized block
private void subscribe(Object subscriber, SubscriberMethod subscriberMethod) {
（1）获取订阅方法的订阅事件
Class<?> eventType = subscriberMethod.eventType;
（2）订阅者和订阅者方法构造Subscription对象
Subscription newSubscription = new Subscription(subscriber, subscriberMethod);
（3）通过订阅事件找到所有Subscription对象
CopyOnWriteArrayList<Subscription> subscriptions = subscriptionsByEventType.get(eventType);
if (subscriptions == null) {
（4）没有找到就放入上面的Subscription对象
subscriptions = new CopyOnWriteArrayList<>();
subscriptionsByEventType.put(eventType, subscriptions);
} else {
（5）不为空就判断是否已经放入，不能多次放入（父子同时注册）
if (subscriptions.contains(newSubscription)) {
throw new EventBusException("Subscriber " + subscriber.getClass() + " already registered to event "
+ eventType);
}
}
（6）按照订阅事件的优先级插入合适的位置
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;
}
}
（7）找到当前订阅者所有的订阅事件
List<Class<?>> subscribedEvents = typesBySubscriber.get(subscriber);
if (subscribedEvents == null) {
subscribedEvents = new ArrayList<>();
typesBySubscriber.put(subscriber, subscribedEvents);
}
subscribedEvents.add(eventType);
（8）粘性事件
if (subscriberMethod.sticky) {
（9）是否支持继承关系，默认为true。
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>).
（10）推荐，尤其是容量大时用entrySet遍历
Set<Map.Entry<Class<?>, Object>> entries = stickyEvents.entrySet();
for (Map.Entry<Class<?>, Object> entry : entries) {
Class<?> candidateEventType = entry.getKey();
（11） isAssignableFrom：判定此 Class 对象所表示的类
或接口与指定的 Class 参数所表示的类或接口是否相同，或是否是其超类或超接口。
如果是则返回 true；否则返回 false。
if (eventType.isAssignableFrom(candidateEventType)) {
(12) 获取粘性事件
Object stickyEvent = entry.getValue();
（13）处理粘性事件
checkPostStickyEventToSubscription(newSubscription, stickyEvent);
}
}
} else {
（14）获取粘性事件
Object stickyEvent = stickyEvents.get(eventType);
（15）处理粘性事件
checkPostStickyEventToSubscription(newSubscription, stickyEvent);
}
}
}
订阅总结：
- 首先判断是否注册过这个事件。不允许多次注册。
- 按照订阅的优先级，添加到
subscriptionsByEventType这个集合当中。 - 添加到
typesBySubscriber这个Map当中。 - 如果是粘性事件，分发事件。
粘性事件
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());
}
}
private void postToSubscription(Subscription subscription, Object event, boolean isMainThread) {
switch (subscription.subscriberMethod.threadMode) {
case POSTING:
（1）直接反射分发，默认的线程模式，哪个线程发送就在哪个线程处理。
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
（2）没有mainThreadPoster就直接反射。
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);
}
}
代码很简单，不做过多解释。
发送事件
EventBus.getDefault().post(new MessageEvent());
public void post(Object event) {
（1）从ThreadLocal中获取PostingThreadState，看下PostingThreadState
PostingThreadState postingState = currentPostingThreadState.get();
List<Object> eventQueue = postingState.eventQueue;
（2）添加到队列
eventQueue.add(event);
（3）是否正在发送
if (!postingState.isPosting) {
postingState.isMainThread = isMainThread();
postingState.isPosting = true;
if (postingState.canceled) {
throw new EventBusException("Internal error. Abort state was not reset");
}
try {
（4）将队列的事件全部分发
while (!eventQueue.isEmpty()) {
（5）重点看下postSingleEvent
postSingleEvent(eventQueue.remove(0), postingState);
}
} finally {
postingState.isPosting = false;
postingState.isMainThread = false;
}
}
}
（1）当前线程Post信息的封装类
final static class PostingThreadState {
（1）事件队列
final List<Object> eventQueue = new ArrayList<>();
（2）是否正在发送
boolean isPosting;
（3）是否主线程
boolean isMainThread;
（4）订阅者和订阅方法的封装类
Subscription subscription;
（5）事件
Object event;
（6）是否取消了
boolean canceled;
}
private void postSingleEvent(Object event, PostingThreadState postingState) throws Error {
Class<?> eventClass = event.getClass();
boolean subscriptionFound = false;
if (eventInheritance) {
（1）寻找订阅事件所有父类和接口
List<Class<?>> eventTypes = lookupAllEventTypes(eventClass);
int countTypes = eventTypes.size();
for (int h = 0; h < countTypes; h++) {
Class<?> clazz = eventTypes.get(h);
（2）看下这个方法postSingleEventForEventType
subscriptionFound |= postSingleEventForEventType(event, postingState, clazz);
}
} else {
subscriptionFound = postSingleEventForEventType(event, postingState, eventClass);
}
（3）没有找到订阅者
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) {
（1）找到所有订阅者
subscriptions = subscriptionsByEventType.get(eventClass);
}
（2）遍历分发事件
if (subscriptions != null && !subscriptions.isEmpty()) {
for (Subscription subscription : subscriptions) {
postingState.event = event;
postingState.subscription = subscription;
boolean aborted;
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;
}
粘性事件发送
public void postSticky(Object event) {
synchronized (stickyEvents) {
先添加到集合
stickyEvents.put(event.getClass(), event);
}
// Should be posted after it is putted, in case the subscriber wants to remove immediately
post(event);
}
发送事件总结：
- 从ThreadLocal获取当前线程的事件发送的封装类。
- 将事件添加到封装类的队列里面。
- 依次分发队列里面的所有事件。
特别注意
- 默认会分发事件的所有父类和接口和接口的父接口。
