2.2Subscriber向Eventbus注冊自己
2.2.1 register方法
接下來看register方法代碼：
public void register(Object subscriber) {
//獲得訂閱者的class對象
Class<?> subscriberClass = subscriber.getClass();
//根據訂閱者對象的Class對象查找當前訂閱者的訂閱方法(所有事件響應函數)
List<SubscriberMethod> subscriberMethods = subscriberMethodFinder.findSubscriberMethods(subscriberClass);
synchronized (this) {
for (SubscriberMethod subscriberMethod : subscriberMethods) {
//循環每個事件響應函數
subscribe(subscriber, subscriberMethod);
}
}
}
subscriberClass就是訂閱者所屬的Class,如MainActivity.class，之后利用subscriberMethodFinder查找subscriberClass中的所有事件響應函數，先了解下SubscriberMethod類：
public class SubscriberMethod {
final Method method;//方法
final ThreadMode threadMode;//執行線程
final Class<?> eventType;//接收的事件類型
final int priority;//優先級
final boolean sticky;
....
}
SubscriberMethod類中封裝了某個事件響應函數的信息，包括：Method對象、執行環境、接收的事件類型、優先級和是否是sticky事件。
2.2.2 SubscriberMethodFinder的實現
SubscriberMethodFinder類用來查找和緩存訂閱者中的訂閱方法(事件響應函數)的信息類。
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對象,value:保存訂閱類中所有訂閱方法(事件響應函數)。
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) {
//在運行時利用反射來獲得訂閱類中的所有訂閱方法(事件響應函數)
subscriberMethods = findUsingReflection(subscriberClass);
} else {
//在編譯時從注解器生成的索引類(MyEventBusIndex)中獲得所有訂閱方法(事件響應函數)
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(事件響應函數)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(事件響應函數)信息，如果沒有則通過以下兩種方式來獲取：
1、在編譯時，通過EventBusAnnotationProcessor（注解處理器）結合@Subscriber所注解方法生成的MyEventBusIndex類中獲取。
有關于這種方式請到這：EventBus3.0新特性之Subscriber Index
2、在運行時，通過反射來獲取訂閱類中訂閱方法(事件響應函數)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) {
//真正的通過反射來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其實就是一個封裝了訂閱相關信息的類，最終是通過findUsingReflectionInSingleClass()來具體獲得相關訂閱方法的信息的:
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類型數組比getMethods方法更快，特別是當在訂閱者是胖類比如像activity時。
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類型數組時，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方法參數
if (parameterTypes.length == 1) {
//判斷此方法對象是否有被Subscribe注解
Subscribe subscribeAnnotation = method.getAnnotation(Subscribe.class);
if (subscribeAnnotation != null) {
Class<?> eventType = parameterTypes[0];
//校驗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");
}
}
}
此方法執行完后，我們訂閱類的所有訂閱方法都已經被保存在FindState對象，最后再通過getMethodsAndRelease()解析得到List<SubscriberMethod>。
至此，通過反射獲取訂閱方法信息這種方式已經分析完了。
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);
//不只是獲得當前訂閱信息，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 {
//如果發現獲取不到subscriberInfo的話,就還是要使用反射來獲取。
findUsingReflectionInSingleClass(findState);
}
//會切換findState.clazz對象為父類的Class對象
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類型數組。SubscriberInfoIndex是一個接口，MyEventBusIndex實現了這個接口。
subscriberInfoIndexes是在執行addIndex方法被初始化并把MyEventBusIndex對象添加到此集合中。
EventBus eventBus = EventBus.builder().addIndex(new MyEventBusIndex())；
/** 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，以findState.clazz(訂閱者的class對象)為key，在MyEventBusIndex.SUBSCRIBER_INDEX中查找，如果查找到了則直接返回。
至此，通過索引類獲取訂閱方法信息這種方式已經分析完了。
2.2.3 subscribe
回到2.2.1 register方法，在獲取subscriberMethods之后，就是遍歷各訂閱方法，并執行subscribe方法。
private void subscribe(Object subscriber, SubscriberMethod subscriberMethod) {
//獲取訂閱方法(事件響應函數)的事件類型
Class<?> eventType = subscriberMethod.eventType;
Subscription newSubscription = new Subscription(subscriber, subscriberMethod);
//從subscriptionsByEventType里檢查是否已經添加過該Subscription,如果添加過就拋出異常
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++) {
//根據優先級priority將當前訂閱者信息插入到訂閱者隊列中
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<>();
//把訂閱者對象作為key，對應訂閱的事件類型集合作為value，保存到typesBySubscriber中。
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sticky事件
if (subscriberMethod.sticky) {
//eventInheritance 表示是否分發訂閱了事件的父類的事件響應函數
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行綁定。
- 訂閱對象與所有訂閱的事件類型進行綁定
- 對sticky事件進行相關處理
至此，完成對[2.2Subscriber向Eventbus注冊自己]過程的源碼分析。
Subscriber向Eventbus注冊自己的執行流程圖：
register方法執行流程圖
