回顾下EventBus的源码
EventBus.getDefault().register(this);
从这行代码出发 首先是geDefault。使用了单例模式 返回了eventbus的实例对象
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;
}
接着看register方法
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.");
}
//订阅者的Class对象 如demo中的MainActivity
Class<?> subscriberClass = subscriber.getClass();
List<SubscriberMethod> subscriberMethods = subscriberMethodFinder.findSubscriberMethods(subscriberClass);
synchronized (this) {
for (SubscriberMethod subscriberMethod : subscriberMethods) {
subscribe(subscriber, subscriberMethod);
}
}
}
调用了SubscriberMethodFinder对象的findSubscriberMethods()方法。METHOD_CACHE是一个缓存的Map集合， Map<Class<?>, List<SubscriberMethod>> METHOD_CACHE = new ConcurrentHashMap<>(); 以前面register方法传进来的subscriber对象的class对象做为key，如果map中已经有这个class对应的SubscribeMethod集合数据了，就直接从缓存中返回。否则 调用findUsingReflection（）或者findUsingInfo（）方法获取。
List<SubscriberMethod> findSubscriberMethods(Class<?> subscriberClass) {
List<SubscriberMethod> subscriberMethods = METHOD_CACHE.get(subscriberClass);
if (subscriberMethods != null) {
return subscriberMethods;
}
//默认为false。这是配置开启apt的方式
if (ignoreGeneratedIndex) {
subscriberMethods = findUsingReflection(subscriberClass);
} else {
subscriberMethods = findUsingInfo(subscriberClass);
}
if (subscriberMethods.isEmpty()) {
throw new EventBusException("Subscriber " + subscriberClass
+ " and its super classes have no public methods with the @Subscribe annotation");
} else {
METHOD_CACHE.put(subscriberClass, subscriberMethods);
return subscriberMethods;
}
}
先看findUsingInfo方法。首先拿到一个FindState对象，再进行初始化。（FindState是通过享元模式拿到的共享对象，所以进行初始化）
private List<SubscriberMethod> findUsingInfo(Class<?> subscriberClass) {
FindState findState = prepareFindState();
findState.initForSubscriber(subscriberClass);
while (findState.clazz != null) {
findState.subscriberInfo = getSubscriberInfo(findState);
if (findState.subscriberInfo != null) {
SubscriberMethod[] array = findState.subscriberInfo.getSubscriberMethods();
for (SubscriberMethod subscriberMethod : array) {
if (findState.checkAdd(subscriberMethod.method, subscriberMethod.eventType)) {
findState.subscriberMethods.add(subscriberMethod);
}
}
} else {
findUsingReflectionInSingleClass(findState);
}
findState.moveToSuperclass();
}
return getMethodsAndRelease(findState);
}
//享元设计模式 通过共享对象避免多次new对象
private FindState prepareFindState() {
synchronized (FIND_STATE_POOL) {
for (int i = 0; i < POOL_SIZE; i++) {
FindState state = FIND_STATE_POOL[i];
if (state != null) {
FIND_STATE_POOL[i] = null;
return state;
}
}
}
return new FindState();
}
第一次循环时 findState.subscriberInfo 是为null，因此接下来调用了findUsingReflectionInSingleClass方法。
总结该方法 通过反射获取订阅者的所有方法，并通过修饰符、注解、方法参数个数等过滤掉非注册的方法。对注册的方法 将注解的各项值（threadMode、priority、sticky等等）封装成subscribeInfo。并添加到集合当中
private void findUsingReflectionInSingleClass(FindState findState) {
Method[] methods;
try {
// This is faster than getMethods, especially when subscribers are fat classes like Activities
methods = findState.clazz.getDeclaredMethods();
} catch (Throwable th) {
// Workaround for java.lang.NoClassDefFoundError, see https://github.com/greenrobot/EventBus/issues/149
try {
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;
}
for (Method method : methods) {
int modifiers = method.getModifiers();
//public 且不是抽象、静态等等
if ((modifiers & Modifier.PUBLIC) != 0 && (modifiers & MODIFIERS_IGNORE) == 0) {
//获取方法的参数
Class<?>[] parameterTypes = method.getParameterTypes();
//方法参数个数只能为1个
if (parameterTypes.length == 1) {
//获取方法上的Subscribe注解
Subscribe subscribeAnnotation = method.getAnnotation(Subscribe.class);
if (subscribeAnnotation != null) {
//获取方法参数的类型
Class<?> eventType = parameterTypes[0];
if (findState.checkAdd(method, eventType)) {
//获取注解上的threadMode类型
ThreadMode threadMode = subscribeAnnotation.threadMode();
//封装成subscribeMethod 并加入到集合当中
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");
}
}
}
上述过程简单总结 就是拿到订阅者的所有已订阅的方法 以SubscriberMethod集合方法返回。
接着看register方法的后半部分。遍历方法调用subscribe方法。看一下这个方法
synchronized (this) {
for (SubscriberMethod subscriberMethod : subscriberMethods) {
subscribe(subscriber, subscriberMethod);
}
}
/**
*
* @param subscriber 订阅者的clazz对象 譬如MainActivity.class
* @param subscriberMethod 订阅者所注册的方法
*/
private void subscribe(Object subscriber, SubscriberMethod subscriberMethod) {
//注册的方法的参数类型
Class<?> eventType = subscriberMethod.eventType;
Subscription newSubscription = new Subscription(subscriber, subscriberMethod);
//以eventType为key ，Subscription集合为value的hashmap数据结构
CopyOnWriteArrayList<Subscription> subscriptions = subscriptionsByEventType.get(eventType);
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);
}
}
//newSubscription添加到Subscription集合中，考虑优先级 priority
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;
}
}
//以订阅者对象为key，eventype集合为value的map集合
List<Class<?>> subscribedEvents = typesBySubscriber.get(subscriber);
if (subscribedEvents == null) {
subscribedEvents = new ArrayList<>();
typesBySubscriber.put(subscriber, subscribedEvents);
}
subscribedEvents.add(eventType);
//处理粘性事件
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 {
//发布粘性事件 会将事件存在集合当中。如果此时有该类型的粘性事件 便取出它的参数的值 立马调用
Object stickyEvent = stickyEvents.get(eventType);
checkPostStickyEventToSubscription(newSubscription, stickyEvent);
}
}
}
总结
register方法 就是对订阅者事件的处理。最终处理成图中的两种数据。
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