可用於應用內的消息事件傳遞,方便快捷,耦合性低java
public class EventBusMain extends AppCompatActivity {
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.content_main);
EventBus.getDefault().register(this);
}
- 訂閱的事件 onEvent1
@Subscribe
public void onEvent1(RemindBean bean){
}
- 訂閱的事件 onEvent2
@Subscribe
public void onEvent2(UserInfo bean){
}
@Override
protected void onDestroy() {
super.onDestroy();
EventBus.getDefault().unregister(this);
}
}
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須要發送消息傳遞的時候:git
EventBus.getDefault().post(new RemindBean())
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放上官網的一張原理圖,感受挺清晰的:github
發佈消息的一方(Publisher
),只須要 post
一個 event
以後就不用管了,EventBus
內部會將event
逐一分發給訂閱此 event
的訂閱者(Subscriber
). 不錯就是這樣一個東西。緩存
還記得以往我要實現兩個不一樣的activity
之間要傳遞一些數據的時候,我都是經過定義一個interface
的形式完成,時間一長,定義的接口一堆,在回顧查看代碼也確實不夠美觀。好了話很少說,看下你們都在用的Eventbus
.bash
EventBus.getDefault().register(this);
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getDefault()
:app
EventBus 是一個單例模式,懶漢式,雙重判斷
/** Convenience singleton for apps using a process-wide EventBus instance. */
public static EventBus getDefault() {
if (defaultInstance == null) {
synchronized (EventBus.class) {
if (defaultInstance == null) {
defaultInstance = new EventBus();
}
}
}
return defaultInstance;
}
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register
是什麼意思呢,就是就跟你訂閱報紙同樣,報社須要肯定幾個重要的問題:async
Subscriber
)?Event
) ?就是我認爲比較重要的,那麼register
這一步就是Subscriber
告訴 報社,訂閱的event
ide
public void register(Object subscriber) {
- 1.先拿到這個訂閱者(subscriber)類的字節碼
Class<?> subscriberClass = subscriber.getClass();
- 2. 經過這個類的字節碼,拿到全部的訂閱的 event,存放在List中
List<SubscriberMethod> subscriberMethods = subscriberMethodFinder.findSubscriberMethods(subscriberClass);
synchronized (this) {
- 3. 循環遍歷全部的訂閱的方法,完成subscriber 和 subscriberMethod 的關聯
for (SubscriberMethod subscriberMethod : subscriberMethods) {
subscribe(subscriber, subscriberMethod);
}
}
}
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咱們看下這個如何根據subscriberClass
找到這個訂閱的 method
的,findSubscriberMethods
:post
List<SubscriberMethod> findSubscriberMethods(Class<?> subscriberClass) {
- 1.先從緩存中取
List<SubscriberMethod> subscriberMethods = METHOD_CACHE.get(subscriberClass);
- 2. 第一次確定 null
if (subscriberMethods != null) {
return subscriberMethods;
}
- 3. 查找默認也是false,感興趣的能夠看下
if (ignoreGeneratedIndex) {
subscriberMethods = findUsingReflection(subscriberClass);
} else {
- 4. 因此是走這裏
subscriberMethods = findUsingInfo(subscriberClass);
}
if (subscriberMethods.isEmpty()) {
throw new EventBusException("Subscriber " + subscriberClass
+ " and its super classes have no public methods with the @Subscribe annotation");
} else {
- 5. 找到以後添加到緩存中,key是 subscriber ;value 是:methods
METHOD_CACHE.put(subscriberClass, subscriberMethods);
return subscriberMethods;
}
}
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看下:findUsingInfo(subscriberClass)
ui
private List<SubscriberMethod> findUsingInfo(Class<?> subscriberClass) {
- 1. 我認爲就是準備一個查找結果得存儲對象
FindState findState = prepareFindState();
- 2. 將訂閱者的subscriberClass 存儲起來,保存在一個FindState 類中的subscriberClass
同時賦值給clazz變量中,如下代碼可以看出
// void initForSubscriber(Class<?> subscriberClass) {
// this.subscriberClass = clazz = subscriberClass;
//}
findState.initForSubscriber(subscriberClass);
while (findState.clazz != null) {進入循環中
//獲取subscriberInfo 信息,返回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 {
- 3. 進入到這裏了
findUsingReflectionInSingleClass(findState);
}
- 4. 查找父類中的方法
findState.moveToSuperclass();
}
return getMethodsAndRelease(findState);
}
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findUsingReflectionInSingleClass
以下:
private void findUsingReflectionInSingleClass(FindState findState) {
Method[] methods;
try {
// This is faster than getMethods, especially when subscribers are fat classes like Activities
- 1. 經過訂閱者的字節碼查找當前類中全部生命的方法
methods = findState.clazz.getDeclaredMethods();
} catch (Throwable th) {
// Workaround for java.lang.NoClassDefFoundError, see https://github.com/greenrobot/EventBus/issues/149
methods = findState.clazz.getMethods();
findState.skipSuperClasses = true;
}
- 2. 循環遍歷全部的方法
for (Method method : methods) {
- 3. 獲取方法的修飾符
int modifiers = method.getModifiers();
- 4.判斷修飾符,訂閱方法的修飾符不能是private,static
if ((modifiers & Modifier.PUBLIC) != 0 && (modifiers & MODIFIERS_IGNORE) == 0) {
- 5. 獲取方法的全部的參數
Class<?>[] parameterTypes = method.getParameterTypes();
- 6.判斷參數的個數,只能有1個參數,訂閱方法中
if (parameterTypes.length == 1) {
- 7.獲取方法上具備subscribe 註解
Subscribe subscribeAnnotation = method.getAnnotation(Subscribe.class);
- 8.含有subscribe註解的方法,就是該類訂閱的方法,其它不符合的可能就是普通的方法
if (subscribeAnnotation != null) {
- 9. 獲取第一個參數eventType
Class<?> eventType = parameterTypes[0];
if (findState.checkAdd(method, eventType)) {
- 10. 獲取註解的mode,就是咱們在註解上標識的,
有mainThread,Posting,background,async
ThreadMode threadMode = subscribeAnnotation.threadMode();
- 11. 將訂閱方法的一系列信息(方法名稱,threadMode,優先級,是不是粘性等)添加到集合subscriberMethods中去
findState.subscriberMethods.add(new SubscriberMethod(method, eventType, threadMode,
subscribeAnnotation.priority(), subscribeAnnotation.sticky()));
}
}
} else if (strictMethodVerification && method.isAnnotationPresent(Subscribe.class)) {
- 12. 參數是多個的時候拋出異常
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)) {
- 13. 方法的修飾符不是public的,拋出異常
String methodName = method.getDeclaringClass().getName() + "." + method.getName();
throw new EventBusException(methodName +
" is a illegal @Subscribe method: must be public, non-static, and non-abstract");
}
}
}
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這樣咱們將全部信息都保存到findState
類中去了。再回頭看咱們原先那個方法,到第三步了:
private List<SubscriberMethod> findUsingInfo(Class<?> subscriberClass) {
- 1. 我認爲就是準備一個查找結果得存儲對象
FindState findState = prepareFindState();
- 2. 將訂閱者的subscriberClass 存儲起來,保存在一個FindState 類中的subscriberClass
同時賦值給clazz變量中,如下代碼可以看出
// void initForSubscriber(Class<?> subscriberClass) {
// this.subscriberClass = clazz = subscriberClass;
//}
findState.initForSubscriber(subscriberClass);
while (findState.clazz != null) {進入循環中
//獲取subscriberInfo 信息,返回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 {
- 3. 進入到這裏了,上面已經分析全部信息保存到findState中
findUsingReflectionInSingleClass(findState);
}
- 4. 查找父類中的方法
findState.moveToSuperclass();
}
return getMethodsAndRelease(findState);
}
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在這個getMethodsAndRelease(findState)
:
private List<SubscriberMethod> getMethodsAndRelease(FindState findState) {
- 1. 取出裏面的subscriberMethods
List<SubscriberMethod> subscriberMethods = new ArrayList<>(findState.subscriberMethods);
findState.recycle();
synchronized (FIND_STATE_POOL) {
for (int i = 0; i < POOL_SIZE; i++) {
if (FIND_STATE_POOL[i] == null) {
FIND_STATE_POOL[i] = findState;
break;
}
}
}
- 2. 返回集合
return subscriberMethods;
}
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至此,咱們知道了根據訂閱者(subscriber
)的clazz
找到了全部訂閱的方法事件 methods
回到最初的第一步register
:
public void register(Object subscriber) {
Class<?> subscriberClass = subscriber.getClass();
- 2. 完成
List<SubscriberMethod> subscriberMethods = subscriberMethodFinder.findSubscriberMethods(subscriberClass);
synchronized (this) {
for (SubscriberMethod subscriberMethod : subscriberMethods) {
- 3.循環遍歷全部的訂閱方法和訂閱者之間創建關聯
subscribe(subscriber, subscriberMethod);
}
}
}
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subscribe(subscriber, subscriberMethod)
方法:
// Must be called in synchronized block
private void subscribe(Object subscriber, SubscriberMethod subscriberMethod) {
- 1. 訂閱方法的eventType的字節碼
Class<?> eventType = subscriberMethod.eventType;
- 2. 訂閱者和訂閱方法封裝成一個Subscription 對象
Subscription newSubscription = new Subscription(subscriber, subscriberMethod);
- 3. subscriptionsByEventType 第一次也是null ,根據eventType
CopyOnWriteArrayList<Subscription> subscriptions = subscriptionsByEventType.get(eventType);
- 4. 第一次確定爲null
if (subscriptions == null) {
subscriptions = new CopyOnWriteArrayList<>();
- 5. key 爲 eventType, value 是subscriptions對象
subscriptionsByEventType.put(eventType, subscriptions);
} else {
- 拋出異常
if (subscriptions.contains(newSubscription)) {
throw new EventBusException("Subscriber " + subscriber.getClass() + " already registered to event "
+ eventType);
}
}
- 6. 獲取全部添加的subscriptions
int size = subscriptions.size();
for (int i = 0; i <= size; i++) {
- 7. 會判斷每一個訂閱方法的優先級,添加到這個 subscriptions中,按照優先級
if (i == size || subscriberMethod.priority > subscriptions.get(i).subscriberMethod.priority) {
subscriptions.add(i, newSubscription);
break;
}
}
- 8.獲取訂閱的方法集合
List<Class<?>> subscribedEvents = typesBySubscriber.get(subscriber);
if (subscribedEvents == null) {
subscribedEvents = new ArrayList<>();
- 9. 爲空添加到 typesBySubscriber
typesBySubscriber.put(subscriber, subscribedEvents);
}
- 10. 訂閱事件添加到subscribedEvents集合中去
subscribedEvents.add(eventType);
- 11. 判斷是不是粘性事件的關聯
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);
}
}
}
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到此,若是你跟着我一步步看到這裏,應該大概明白一些了,還有一部分沒完,就是register
前半部分完成訂閱,存儲等工做;剩下post(event)
方法就是將event
分發給相應訂閱過此事件的訂閱者了。