2.2Subscriber向Eventbus注冊(cè)自己
2.2.1 register方法
接下來(lái)看register方法代碼：
public void register(Object subscriber) {
//獲得訂閱者的class對(duì)象
Class<?> subscriberClass = subscriber.getClass();
//根據(jù)訂閱者對(duì)象的Class對(duì)象查找當(dāng)前訂閱者的訂閱方法(所有事件響應(yīng)函數(shù))
List<SubscriberMethod> subscriberMethods = subscriberMethodFinder.findSubscriberMethods(subscriberClass);
synchronized (this) {
for (SubscriberMethod subscriberMethod : subscriberMethods) {
//循環(huán)每個(gè)事件響應(yīng)函數(shù)
subscribe(subscriber, subscriberMethod);
}
}
}
subscriberClass就是訂閱者所屬的Class,如MainActivity.class，之后利用subscriberMethodFinder查找subscriberClass中的所有事件響應(yīng)函數(shù)刊橘，先了解下SubscriberMethod類：
public class SubscriberMethod {
final Method method;//方法
final ThreadMode threadMode;//執(zhí)行線程
final Class<?> eventType;//接收的事件類型
final int priority;//優(yōu)先級(jí)
final boolean sticky;
....
}
SubscriberMethod類中封裝了某個(gè)事件響應(yīng)函數(shù)的信息撤蚊，包括：Method對(duì)象敬鬓、執(zhí)行環(huán)境驮吱、接收的事件類型、優(yōu)先級(jí)和是否是sticky事件署拟。
2.2.2 SubscriberMethodFinder的實(shí)現(xiàn)
SubscriberMethodFinder類用來(lái)查找和緩存訂閱者中的訂閱方法(事件響應(yīng)函數(shù))的信息類铁瞒。
SubscriberMethodFinder .findSubscriberMethods()方法如下:
List<SubscriberMethod> findSubscriberMethods(Class<?> subscriberClass) {
//先從METHOD_CACHE查看是否有緩存,key:訂閱類的class對(duì)象,value:保存訂閱類中所有訂閱方法(事件響應(yīng)函數(shù))。
List<SubscriberMethod> subscriberMethods = METHOD_CACHE.get(subscriberClass);
if (subscriberMethods != null) {
return subscriberMethods;
}
//是否忽略注解器生成的索引類(MyEventBusIndex)
if (ignoreGeneratedIndex) {
//在運(yùn)行時(shí)利用反射來(lái)獲得訂閱類中的所有訂閱方法(事件響應(yīng)函數(shù))
subscriberMethods = findUsingReflection(subscriberClass);
} else {
//在編譯時(shí)從注解器生成的索引類(MyEventBusIndex)中獲得所有訂閱方法(事件響應(yīng)函數(shù))
subscriberMethods = findUsingInfo(subscriberClass);
}
if (subscriberMethods.isEmpty()) {
throw new EventBusException("Subscriber " + subscriberClass
+ " and its super classes have no public methods with the @Subscribe annotation");
} else {
//把訂閱類中所有訂閱方法(事件響應(yīng)函數(shù))緩存到METHOD_CACHE
METHOD_CACHE.put(subscriberClass, subscriberMethods);
return subscriberMethods;
}
}
該方法首先從緩存中獲取訂閱類的訂閱方法(事件響應(yīng)函數(shù))信息新娜，如果沒有則通過(guò)以下兩種方式來(lái)獲日栽：
1、在編譯時(shí)杯活，通過(guò)EventBusAnnotationProcessor（注解處理器）結(jié)合@Subscriber所注解方法生成的MyEventBusIndex類中獲取匆帚。
有關(guān)于這種方式請(qǐng)到這：EventBus3.0新特性之Subscriber Index
2、在運(yùn)行時(shí)旁钧，通過(guò)反射來(lái)獲取訂閱類中訂閱方法(事件響應(yīng)函數(shù))的信息
2.2.2 使用反射獲取訂閱信息
private List<SubscriberMethod> findUsingReflection(Class<?> subscriberClass) {
SubscriberMethodFinder.FindState findState = prepareFindState();
findState.initForSubscriber(subscriberClass);
while (findState.clazz != null) {
//真正的通過(guò)反射來(lái)獲得訂閱方法信息邏輯
findUsingReflectionInSingleClass(findState);
//查找父類的訂閱方法
findState.moveToSuperclass();
}
// 獲取findState中的subscriberMethods(也就是訂閱方法List)并返回
return getMethodsAndRelease(findState);
}
FindState其實(shí)就是一個(gè)封裝了訂閱相關(guān)信息的類吸重，最終是通過(guò)findUsingReflectionInSingleClass()來(lái)具體獲得相關(guān)訂閱方法的信息的:
private void findUsingReflectionInSingleClass(SubscriberMethodFinder.FindState findState) {
Method[] methods;
try {
// This is faster than getMethods, especially when subscribers are fat classes like Activities
//這種方式獲取Method類型數(shù)組比getMethods方法更快，特別是當(dāng)在訂閱者是胖類比如像activity時(shí)歪今。
methods = findState.clazz.getDeclaredMethods();
} catch (Throwable th) {
// Workaround for java.lang.NoClassDefFoundError, see https://github.com/greenrobot/EventBus/issues/149
//如果getDeclaredMethods方式獲取Method類型數(shù)組時(shí)嚎幸，拋出異常則改為使用getMethods方式獲取到訂閱類中的所有方法
methods = findState.clazz.getMethods();
findState.skipSuperClasses = true;
}
for (Method method : methods) {
int modifiers = method.getModifiers();
//選擇是public和非static,非abstract,非bridge,非synthetic的方法
if ((modifiers & Modifier.PUBLIC) != 0 && (modifiers & MODIFIERS_IGNORE) == 0) {
Class<?>[] parameterTypes = method.getParameterTypes();
//保證訂閱方法只有一個(gè)方法參數(shù)
if (parameterTypes.length == 1) {
//判斷此方法對(duì)象是否有被Subscribe注解
Subscribe subscribeAnnotation = method.getAnnotation(Subscribe.class);
if (subscribeAnnotation != null) {
Class<?> eventType = parameterTypes[0];
//校驗(yàn)是否添加該訂閱方法
if (findState.checkAdd(method, eventType)) {
ThreadMode threadMode = subscribeAnnotation.threadMode();
//添加訂閱方法
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");
}
}
}
此方法執(zhí)行完后，我們訂閱類的所有訂閱方法都已經(jīng)被保存在FindState對(duì)象寄猩，最后再通過(guò)getMethodsAndRelease()解析得到List<SubscriberMethod>嫉晶。
至此，通過(guò)反射獲取訂閱方法信息這種方式已經(jīng)分析完了。
2.2.3 使用EventBusAnnotationProcessor獲取訂閱信息
private List<SubscriberMethod> findUsingInfo(Class<?> subscriberClass) {
SubscriberMethodFinder.FindState findState = prepareFindState();
findState.initForSubscriber(subscriberClass);
//不只是獲得當(dāng)前訂閱信息替废，還要獲得其到頂層父類的所有訂閱信息
while (findState.clazz != null) {
findState.subscriberInfo = getSubscriberInfo(findState);
if (findState.subscriberInfo != null) {
SubscriberMethod[] array = findState.subscriberInfo.getSubscriberMethods();
for (SubscriberMethod subscriberMethod : array) {
//檢查是否添加過(guò)此訂閱方法
if (findState.checkAdd(subscriberMethod.method, subscriberMethod.eventType)) {
//添加訂閱方法
findState.subscriberMethods.add(subscriberMethod);
}
}
} else {
//如果發(fā)現(xiàn)獲取不到subscriberInfo的話,就還是要使用反射來(lái)獲取箍铭。
findUsingReflectionInSingleClass(findState);
}
//會(huì)切換findState.clazz對(duì)象為父類的Class對(duì)象
findState.moveToSuperclass();
}
return getMethodsAndRelease(findState);
}
查看getSubscriberInfo()：
private SubscriberInfo getSubscriberInfo(FindState findState) {
if (findState.subscriberInfo != null && findState.subscriberInfo.getSuperSubscriberInfo() != null) {
SubscriberInfo superclassInfo = findState.subscriberInfo.getSuperSubscriberInfo();
if (findState.clazz == superclassInfo.getSubscriberClass()) {
return superclassInfo;
}
}
if (subscriberInfoIndexes != null) {
for (SubscriberInfoIndex index : subscriberInfoIndexes) {
SubscriberInfo info = index.getSubscriberInfo(findState.clazz);
if (info != null) {
return info;
}
}
}
return null;
}
subscriberInfoIndexes是屬于SubscriberInfoIndex類型數(shù)組。SubscriberInfoIndex是一個(gè)接口椎镣，MyEventBusIndex實(shí)現(xiàn)了這個(gè)接口诈火。
subscriberInfoIndexes是在執(zhí)行addIndex方法被初始化并把MyEventBusIndex對(duì)象添加到此集合中。
EventBus eventBus = EventBus.builder().addIndex(new MyEventBusIndex())状答；
/** Adds an index generated by EventBus' annotation preprocessor. */
public EventBusBuilder addIndex(SubscriberInfoIndex index) {
if(subscriberInfoIndexes == null) {
subscriberInfoIndexes = new ArrayList<>();
}
subscriberInfoIndexes.add(index);
return this;
}
MyEventBusIndex起作用是在SubscriberMethodFinder的getSubscriberInfo()中冷守，以findState.clazz(訂閱者的class對(duì)象)為key，在MyEventBusIndex.SUBSCRIBER_INDEX中查找惊科，如果查找到了則直接返回拍摇。
至此，通過(guò)索引類獲取訂閱方法信息這種方式已經(jīng)分析完了馆截。
2.2.3 subscribe
回到2.2.1 register方法充活，在獲取subscriberMethods之后，就是遍歷各訂閱方法孙咪，并執(zhí)行subscribe方法堪唐。
private void subscribe(Object subscriber, SubscriberMethod subscriberMethod) {
//獲取訂閱方法(事件響應(yīng)函數(shù))的事件類型
Class<?> eventType = subscriberMethod.eventType;
Subscription newSubscription = new Subscription(subscriber, subscriberMethod);
//從subscriptionsByEventType里檢查是否已經(jīng)添加過(guò)該Subscription,如果添加過(guò)就拋出異常
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);
}
}
int size = subscriptions.size();
for (int i = 0; i <= size; i++) {
//根據(jù)優(yōu)先級(jí)priority將當(dāng)前訂閱者信息插入到訂閱者隊(duì)列中
if (i == size || subscriberMethod.priority > subscriptions.get(i).subscriberMethod.priority) {
subscriptions.add(i, newSubscription);
break;
}
}
//獲取訂閱者所有訂閱的事件類型
List<Class<?>> subscribedEvents = typesBySubscriber.get(subscriber);
if (subscribedEvents == null) {
subscribedEvents = new ArrayList<>();
//把訂閱者對(duì)象作為key，對(duì)應(yīng)訂閱的事件類型集合作為value翎蹈，保存到typesBySubscriber中淮菠。
typesBySubscriber.put(subscriber, subscribedEvents);
}
//將該事件類型添加到typesBySubscriber中
subscribedEvents.add(eventType);
//如果接收sticky事件,立即分發(fā)sticky事件
if (subscriberMethod.sticky) {
//eventInheritance 表示是否分發(fā)訂閱了事件的父類的事件響應(yīng)函數(shù)
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);
}
}
}
在此方法中，主要完成以下事情：
- 事件與訂閱類中訂閱方法進(jìn)行綁定荤堪。
- 訂閱對(duì)象與所有訂閱的事件類型進(jìn)行綁定
- 對(duì)sticky事件進(jìn)行相關(guān)處理
至此合陵，完成對(duì)[2.2Subscriber向Eventbus注冊(cè)自己]過(guò)程的源碼分析。
Subscriber向Eventbus注冊(cè)自己的執(zhí)行流程圖：
register方法執(zhí)行流程圖
