eventBus3.1.1
eventBus主要用于数据之间的传递，使用也非常简单，就几个主要的方法，一个是register和unregister，这两个要成对出现，一般在onCreate中注册，在onDestroy中取消注册。还有几个方法post,postSticky,removeAllStickyEvents。其中post必须在register之后才有效，否则接收不到信息，postSticky可以在register之前和之后都可以。先看一下register方法
/**
* Registers the given subscriber to receive events. Subscribers must call {@link #unregister(Object)} once they
* are no longer interested in receiving events.
* <p/>
* Subscribers have event handling methods that must be annotated by {@link Subscribe}.
* The {@link Subscribe} annotation also allows configuration like {@link
* ThreadMode} and priority.
*/
public void register(Object subscriber) {
Class<?> subscriberClass = subscriber.getClass();
List<SubscriberMethod> subscriberMethods = subscriberMethodFinder.findSubscriberMethods(subscriberClass);
synchronized (this) {
for (SubscriberMethod subscriberMethod : subscriberMethods) {
subscribe(subscriber, subscriberMethod);
}
}
}这里面主要看一下findSubscriberMethods方法，他是找到你所在注册类的注解方法，因为一般情况下要想接收数据，必须要加注解的方法，比如@Subscribe(threadMode = ThreadMode.MAIN)或者@Subscribe(threadMode = ThreadMode.MAIN, sticky = true)，当然你也可以修改threadMode指定在其他线程中操作。
POSTING ：表示发送事件和接收事件在相同的线程
MAIN ：表示在主线程中处理数据
MAIN_ORDERED：和MAIN一样是在主线程中操作，但需要排队
BACKGROUND ：在后台线程中执行
ASYNC ：在另起一个异步线程中执行
List<SubscriberMethod> findSubscriberMethods(Class<?> subscriberClass) {
List<SubscriberMethod> subscriberMethods = METHOD_CACHE.get(subscriberClass);
if (subscriberMethods != null) {
return subscriberMethods;
}
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;
}
}上面代码中ignoreGeneratedIndex默认情况下是false，其中findUsingReflection和findUsingInfo有可能最终调用的都是findUsingReflectionInSingleClass，为啥说是有可能，是因为findUsingInfo取值的时候会从先从subscriberInfoIndexes中取，如果有就返回，没有就会调用findUsingReflectionInSingleClass方法，所以来看一下findUsingInfo方法
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);
}注意这里有个方法moveToSuperclass和上面的while循环，moveToSuperclass是获取FindState字段clazz的父类，就是在当前类中查找之后还要在父类中查找注解的方法，不断往上找，直到父类为空为止。其中FindState是一个数据池FindState的对象，默认值为4，private static final int POOL_SIZE = 4;如果有就从池中取，没有就创建，也是为了提高速度，看一下第一行代码prepareFindState
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();
}来看一下上面的getSubscriberInfo方法，如果获取为空，就会执行findUsingReflectionInSingleClass方法，来看一下getSubscriberInfo的具体实现
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;
}下面的subscriberInfoIndexes是由SubscriberMethodFinder的构造方法传进来的值，这里有一个官方提供的优化方法，就是从subscriberInfoIndexes中取，这个最后在介绍。我们先往上看，会发现无论是findUsingInfo还是findUsingReflection方法，在最后都会调用getMethodsAndRelease方法，我们再来看一下它的具体实现
private List<SubscriberMethod> getMethodsAndRelease(FindState findState) {
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;
}
}
}
return subscriberMethods;
}其实就相当于FindState的回收和订阅方法的返回。下面再来看一下重量级方法findUsingReflectionInSingleClass
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
methods = findState.clazz.getMethods();
findState.skipSuperClasses = true;
}
for (Method method : methods) {
int modifiers = method.getModifiers();
if ((modifiers & Modifier.PUBLIC) != 0 && (modifiers & MODIFIERS_IGNORE) == 0) {
Class<?>[] parameterTypes = method.getParameterTypes();
if (parameterTypes.length == 1) {
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");
}
}
}通过反射的方式找到注解的方法，从上面代码可以看出，注解的方法只能有一个参数，其中checkAdd是根据方法和参数进行验证。然后把找到的存到FindState中。OK，关于注解方法的查找也就这些，下面看回过头来看一下register发具体实现，在subscriberMethodFinder.findSubscriberMethods(subscriberClass)方法查找之后，然后进行遍历
// Must be called in synchronized block
private void subscribe(Object subscriber, SubscriberMethod subscriberMethod) {
Class<?> eventType = subscriberMethod.eventType;
Subscription newSubscription = new Subscription(subscriber, subscriberMethod);
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++) {
if (i == size || subscriberMethod.priority > subscriptions.get(i).subscriberMethod.priority) {
subscriptions.add(i, newSubscription);
break;
}
}
List<Class<?>> subscribedEvents = typesBySubscriber.get(subscriber);
if (subscribedEvents == null) {
subscribedEvents = new ArrayList<>();
typesBySubscriber.put(subscriber, subscribedEvents);
}
subscribedEvents.add(eventType);
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);
}
}
}代码比较简单，这里要记住一下subscriptionsByEventType字段，为什么在register之前post会收不到消息，而在register之前postSticky确能收到消息。因为这里会把当前订阅的方法存入到subscriptionsByEventType中，post的时候如果还没有register，那么subscriptionsByEventType就会为空，当然收不到消息，而postSticky是粘性事件，会保存在stickyEvents中，在register的时候还可以在触发。看一下上面代码的第31行，如果之前发送的是粘性事件，也就是postSticky，那么这里就会执行下面的checkPostStickyEventToSubscription方法。上面的boolean eventInheritance = true;默认值为true。checkPostStickyEventToSubscription方法会调用postToSubscription，来看一下postToSubscription方法
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);
}
}这里就是上面说的几种线程中的操作，看一下MAIN和MAIN_ORDERED。我们以MAIN线程为例继续看，来看一下invokeSubscriber方法
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);
}
}这回是彻底明白了，找到订阅的方法，然后通过反射进行调用。这里只是在register中的调用，他只能调用sticky的事件。下面看一下最主要的两个方法post和postSticky
/**
* Posts the given event to the event bus and holds on to the event (because it is sticky). The most recent sticky
* event of an event's type is kept in memory for future access by subscribers using {@link Subscribe#sticky()}.
*/
public void postSticky(Object event) {
synchronized (stickyEvents) {
stickyEvents.put(event.getClass(), event);
}
// Should be posted after it is putted, in case the subscriber wants to remove immediately
post(event);
}我们看到postSticky调用了post，和post唯一的区别就是他保存了event对象，保存在stickyEvents中，所以postSticky的事件可以在register之前调用原理就在这，把当前订阅的类保存在stickyEvents中，然后register的时候就可以调用，而post没有保存，所以register的时候自然没法触发，这里要注意在上面分析的subscribe方法中，我们知道他只能触发sticky的事件，我们接着往下看post方法
/** Posts the given event to the event bus. */
public void post(Object event) {
PostingThreadState postingState = currentPostingThreadState.get();
List<Object> eventQueue = postingState.eventQueue;
eventQueue.add(event);
if (!postingState.isPosting) {
postingState.isMainThread = isMainThread();
postingState.isPosting = true;
if (postingState.canceled) {
throw new EventBusException("Internal error. Abort state was not reset");
}
try {
while (!eventQueue.isEmpty()) {
postSingleEvent(eventQueue.remove(0), postingState);
}
} finally {
postingState.isPosting = false;
postingState.isMainThread = false;
}
}
}这里就不在过多介绍，主要看一下postSingleEvent方法
private void postSingleEvent(Object event, PostingThreadState postingState) throws Error {
Class<?> eventClass = event.getClass();
boolean subscriptionFound = false;
if (eventInheritance) {
List<Class<?>> eventTypes = lookupAllEventTypes(eventClass);
int countTypes = eventTypes.size();
for (int h = 0; h < countTypes; h++) {
Class<?> clazz = eventTypes.get(h);
subscriptionFound |= postSingleEventForEventType(event, postingState, clazz);
}
} else {
subscriptionFound = postSingleEventForEventType(event, postingState, eventClass);
}
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));
}
}
}接着看postSingleEventForEventType方法
private boolean postSingleEventForEventType(Object event, PostingThreadState postingState, Class<?> eventClass) {
CopyOnWriteArrayList<Subscription> subscriptions;
synchronized (this) {
subscriptions = subscriptionsByEventType.get(eventClass);
}
if (subscriptions != null && !subscriptions.isEmpty()) {
for (Subscription subscription : subscriptions) {
postingState.event = event;
postingState.subscription = subscription;
boolean aborted = false;
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;
}这里我们先看一下postToSubscription，就是上面刚分析的，就不在说了，这里我们来看一下subscriptionsByEventType，我们上面分析的subscriptionsByEventType是在register的时候才会把订阅的事件保存，如果在register之前调用post和postSticky方法，那么这里subscriptionsByEventType返回的自然是空，所以也就不会执行下面的代码了，但postSticky不同，虽然他不能执行，但它把订阅的对象保存在了stickyEvents中，在register的时候就会触发了。下面再来说说上面遗留的问题，上面说道subscriberInfoIndexes中取值的时候的问题，这个字段是在SubscriberMethodFinder构造方法中带过来的，而SubscriberMethodFinder是在EventBus类的构造函数中初始化的，而EventBus的构造函数传入的是EventBusBuilder，使用的是建造者模式，且subscriberInfoIndexes默认为空，我们看一下他传值的方法
/** Adds an index generated by EventBus' annotation preprocessor. */
public EventBusBuilder addIndex(SubscriberInfoIndex index) {
if (subscriberInfoIndexes == null) {
subscriberInfoIndexes = new ArrayList<>();
}
subscriberInfoIndexes.add(index);
return this;
}这个很简单，实际上还可以使用一种更加高效的方法，自动为我们生成一个MyEventBusIndex类，它里面会包含我们注解的方法。具体实现是在app的defaultConfig中添加下面代码
javaCompileOptions {
annotationProcessorOptions {
arguments = [ eventBusIndex : 'com.example.myapp.MyEventBusIndex' ]
}
}然后在dependencies中添加下面代码
implementation 'org.greenrobot:eventbus:3.1.1'
annotationProcessor 'org.greenrobot:eventbus-annotation-processor:3.1.1'就会自动为我们生成一个类，具体位置如下，
这里我写了两个类，每个类都写了两个注解的方法
(threadMode = ThreadMode.MAIN)
public void onReceiveEvent(String event) {
Log.d("wld_____", "FirstActivity：onReceiveEvent1：" + event);
}
(threadMode = ThreadMode.MAIN, sticky = true)
public void onReceiveStickyEvent(String event) {
Log.d("wld_____", "FirstActivity：onReceiveStickyEvent2：" + event);
}和
(threadMode = ThreadMode.MAIN)
public void onReceiveEvent(String event) {
Log.d("wld_____", "SecondActivity：onReceiveEvent：" + event);
}
(threadMode = ThreadMode.MAIN, sticky = true)
public void onReceiveStickyEvent(String event) {
Log.d("wld_____", "SecondActivity：onReceiveStickyEvent：" + event);
}我们来看一下生成的MyEventBusIndex类
package com.example.myapp;
import org.greenrobot.eventbus.meta.SimpleSubscriberInfo;
import org.greenrobot.eventbus.meta.SubscriberMethodInfo;
import org.greenrobot.eventbus.meta.SubscriberInfo;
import org.greenrobot.eventbus.meta.SubscriberInfoIndex;
import org.greenrobot.eventbus.ThreadMode;
import java.util.HashMap;
import java.util.Map;
/** This class is generated by EventBus, do not edit. */
public class MyEventBusIndex implements SubscriberInfoIndex {
private static final Map<Class<?>, SubscriberInfo> SUBSCRIBER_INDEX;
static {
SUBSCRIBER_INDEX = new HashMap<Class<?>, SubscriberInfo>();
putIndex(new SimpleSubscriberInfo(yiquan.xianquan.com.myapplication.SecondActivity.class, true,
new SubscriberMethodInfo[] {
new SubscriberMethodInfo("onReceiveEvent", String.class, ThreadMode.MAIN),
new SubscriberMethodInfo("onReceiveStickyEvent", String.class, ThreadMode.MAIN, 0, true),
}));
putIndex(new SimpleSubscriberInfo(yiquan.xianquan.com.myapplication.FirstActivity.class, true,
new SubscriberMethodInfo[] {
new SubscriberMethodInfo("onReceiveEvent", String.class, ThreadMode.MAIN),
new SubscriberMethodInfo("onReceiveStickyEvent", String.class, ThreadMode.MAIN, 0, true),
}));
}
private static void putIndex(SubscriberInfo info) {
SUBSCRIBER_INDEX.put(info.getSubscriberClass(), info);
}
public SubscriberInfo getSubscriberInfo(Class<?> subscriberClass) {
SubscriberInfo info = SUBSCRIBER_INDEX.get(subscriberClass);
if (info != null) {
return info;
} else {
return null;
}
}
}至于他的使用，可以这样
EventBus.builder().addIndex(new MyEventBusIndex()).installDefaultEventBus();
EventBus eventBus = EventBus.getDefault();这里最好把EventBus.builder().addIndex(new MyEventBusIndex()).installDefaultEventBus();放到Application中，只初始化一次，如果多次初始化会直接抛异常，我们看一下源码
/**
* Installs the default EventBus returned by {@link EventBus#getDefault()} using this builders' values. Must be
* done only once before the first usage of the default EventBus.
*
* @throws EventBusException if there's already a default EventBus instance in place
*/
public EventBus installDefaultEventBus() {
synchronized (EventBus.class) {
if (EventBus.defaultInstance != null) {
throw new EventBusException("Default instance already exists." +
" It may be only set once before it's used the first time to ensure consistent behavior.");
}
EventBus.defaultInstance = build();
return EventBus.defaultInstance;
}
}所以他只能初始化一次。OK，EventBus的原理基本已经分析完毕，下面来看一下具体使用。下面有两个类FirstActivity和SecondActivity，我们暂且标记为A和B
public class FirstActivity extends AppCompatActivity {
private Button button1;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_first);
EventBus.getDefault().register(this);
button1 = findViewById(R.id.button1);
button1.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
EventBus.getDefault().postSticky("111111");
startActivity(new Intent(FirstActivity.this, SecondActivity.class));
}
});
}
(threadMode = ThreadMode.MAIN)
public void onReceiveEvent(String event) {
Log.d("wld_____", "FirstActivity：onReceiveEvent：" + event);
}
(threadMode = ThreadMode.MAIN, sticky = true)
public void onReceiveStickyEvent(String event) {
Log.d("wld_____", "FirstActivity：onReceiveStickyEvent：" + event);
}
protected void onDestroy() {
super.onDestroy();
EventBus.getDefault().unregister(this);
}
}public class SecondActivity extends AppCompatActivity {
private Button button2;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_second);
EventBus.getDefault().register(this);
button2 = findViewById(R.id.button2);
button2.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
finish();
}
});
}
(threadMode = ThreadMode.MAIN)
public void onReceiveEvent(String event) {
Log.d("wld_____", "SecondActivity：onReceiveEvent：" + event);
}
(threadMode = ThreadMode.MAIN, sticky = true)
public void onReceiveStickyEvent(String event) {
Log.d("wld_____", "SecondActivity：onReceiveStickyEvent：" + event);
}
protected void onDestroy() {
super.onDestroy();
EventBus.getDefault().unregister(this);
}
}运行一下，看一下打印的log
结果显然是正确的，因为在A和B中都是先注册，所以会获得他们注解的方法，当在A中发送消息的时候A的两个方法都是可以接收到消息的，但在B中由于B还没有启动，所以当B启动的时候只能接收到sticky注册的方法。改一下代码再看一下
EventBus.getDefault().post("111111");
startActivity(new Intent(FirstActivity.this, SecondActivity.class));看一下打印log，
我们发现只有A的两个方法执行了，B的方法一个也没执行，这个也很好理解，因为B还没有注册就开始发送消息，所以收不到。再来改一下代码看看，调整一下顺序
startActivity(new Intent(FirstActivity.this, SecondActivity.class));
EventBus.getDefault().post("111111");看一下打印log
一样B不会打印，这是因为Activity的启动是耗时的，而B还没启动就开始发送消息，自然是接收不到的，我们再改一下，延迟30毫秒在发送，30毫秒的时间Activity应该完全启动了吧，我们看一下
startActivity(new Intent(FirstActivity.this, SecondActivity.class));
new Handler().postDelayed(new Runnable() {
public void run() {
EventBus.getDefault().post("111111");
}
}, 30);
}再来看一下打印log
看到没，A和B的两个注解的方法都执行了，这是因为延迟之后A和B都已经启动了，但A的onDestroy还没有执行，所以两个类的注解方法都会执行的。OK，到这里EventBus的原理就已经分析完了。
