轉載請標明出處：http://blog.csdn.net/lmj623565791/article/details/40920453，本文出自：【張鴻洋的博客】

上一篇帶大家初步瞭解了EventBus的使用方式，詳見：Android EventBus實戰沒聽過你就out了，本篇博客將解析EventBus的源碼，相信能夠讓大家深入理解該框架的實現，也能解決很多在使用中的疑問：爲什麼可以這麼做？爲什麼這麼做不好呢？

1、概述

一般使用EventBus的組件類，類似下面這種方式：

[java] view plain copy

print?

public class SampleComponent extends Fragment
{
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
EventBus.getDefault().register(this);
}
public void onEventMainThread(param)
{
}
public void onEventPostThread(param)
{
}
public void onEventBackgroundThread(param)
{
}
public void onEventAsync(param)
{
}
@Override
public void onDestroy()
{
super.onDestroy();
EventBus.getDefault().unregister(this);
}
}

public class SampleComponent extends Fragment
{

    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        EventBus.getDefault().register(this);
    }

    public void onEventMainThread(param)
    {
    }

    public void onEventPostThread(param)
    {

    }

    public void onEventBackgroundThread(param)
    {

    }

    public void onEventAsync(param)
    {

    }

    @Override
    public void onDestroy()
    {
        super.onDestroy();
        EventBus.getDefault().unregister(this);
    }

}

大多情況下，都會在onCreate中進行register，在onDestory中進行unregister ；

看完代碼大家或許會有一些疑問：

1、代碼中還有一些以onEvent開頭的方法，這些方法是幹嘛的呢？

在回答這個問題之前，我有一個問題，你咋不問register（this）是幹嘛的呢？其實register(this)就是去當前類，遍歷所有的方法，找到onEvent開頭的然後進行存儲。現在知道onEvent開頭的方法是幹嘛的了吧。

2、那onEvent後面的那些MainThread應該是什麼標誌吧？

嗯，是的，onEvent後面可以寫四種，也就是上面出現的四個方法，決定了當前的方法最終在什麼線程運行，怎麼運行，可以參考上一篇博客或者細細往下看。

既然register了，那麼肯定得說怎麼調用是吧。

[java] view plain copy

print?

EventBus.getDefault().post(param);

EventBus.getDefault().post(param);

調用很簡單，一句話，你也可以叫發佈，只要把這個param發佈出去，EventBus會在它內部存儲的方法中，進行掃描，找到參數匹配的，就使用反射進行調用。

現在有沒有覺得，撇開專業術語：其實EventBus就是在內部存儲了一堆onEvent開頭的方法，然後post的時候，根據post傳入的參數，去找到匹配的方法，反射調用之。

那麼，我告訴你，它內部使用了Map進行存儲，鍵就是參數的Class類型。知道是這個類型，那麼你覺得根據post傳入的參數進行查找還是個事麼？

下面我們就去看看EventBus的register和post真面目。

2、register

EventBus.getDefault().register(this);

首先：

EventBus.getDefault()其實就是個單例，和我們傳統的getInstance一個意思：

[java] view plain copy

print?

/** 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;
}

 /** 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;
    }

使用了雙重判斷的方式，防止併發的問題，還能極大的提高效率。

然後register應該是一個普通的方法，我們去看看：

register公佈給我們使用的有4個：

[java] view plain copy

print?

public void register(Object subscriber) {
register(subscriber, DEFAULT_METHOD_NAME, false, 0);
}
public void register(Object subscriber, int priority) {
register(subscriber, DEFAULT_METHOD_NAME, false, priority);
}
public void registerSticky(Object subscriber) {
register(subscriber, DEFAULT_METHOD_NAME, true, 0);
}
public void registerSticky(Object subscriber, int priority) {
register(subscriber, DEFAULT_METHOD_NAME, true, priority);
}

 public void register(Object subscriber) {
        register(subscriber, DEFAULT_METHOD_NAME, false, 0);
    }
 public void register(Object subscriber, int priority) {
        register(subscriber, DEFAULT_METHOD_NAME, false, priority);
    }
public void registerSticky(Object subscriber) {
        register(subscriber, DEFAULT_METHOD_NAME, true, 0);
    }
public void registerSticky(Object subscriber, int priority) {
        register(subscriber, DEFAULT_METHOD_NAME, true, priority);
    }

本質上就調用了同一個：

[java] view plain copy

print?

private synchronized void register(Object subscriber, String methodName, boolean sticky, int priority) {
List<SubscriberMethod> subscriberMethods = subscriberMethodFinder.findSubscriberMethods(subscriber.getClass(),
methodName);
for (SubscriberMethod subscriberMethod : subscriberMethods) {
subscribe(subscriber, subscriberMethod, sticky, priority);
}
}

private synchronized void register(Object subscriber, String methodName, boolean sticky, int priority) {
        List<SubscriberMethod> subscriberMethods = subscriberMethodFinder.findSubscriberMethods(subscriber.getClass(),
                methodName);
        for (SubscriberMethod subscriberMethod : subscriberMethods) {
            subscribe(subscriber, subscriberMethod, sticky, priority);
        }
    }

四個參數

subscriber 是我們掃描類的對象，也就是我們代碼中常見的this;

methodName 這個是寫死的：“onEvent”，用於確定掃描什麼開頭的方法，可見我們的類中都是以這個開頭。

sticky 這個參數，解釋源碼的時候解釋，暫時不用管

priority 優先級，優先級越高，在調用的時候會越先調用。

下面開始看代碼：

[java] view plain copy

print?

List<SubscriberMethod> subscriberMethods = subscriberMethodFinder.findSubscriberMethods(subscriber.getClass(),
methodName);

List<SubscriberMethod> subscriberMethods = subscriberMethodFinder.findSubscriberMethods(subscriber.getClass(),
                methodName);

調用內部類SubscriberMethodFinder的findSubscriberMethods方法，傳入了subscriber 的class，以及methodName，返回一個List<SubscriberMethod>。

那麼不用說，肯定是去遍歷該類內部所有方法，然後根據methodName去匹配，匹配成功的封裝成SubscriberMethod，最後返回一個List。下面看代碼：

[java] view plain copy

print?

List<SubscriberMethod> findSubscriberMethods(Class<?> subscriberClass, String eventMethodName) {
String key = subscriberClass.getName() + ’.’ + eventMethodName;
List<SubscriberMethod> subscriberMethods;
synchronized (methodCache) {
subscriberMethods = methodCache.get(key);
}
if (subscriberMethods != null) {
return subscriberMethods;
}
subscriberMethods = new ArrayList<SubscriberMethod>();
Class<?> clazz = subscriberClass;
HashSet<String> eventTypesFound = new HashSet<String>();
StringBuilder methodKeyBuilder = new StringBuilder();
while (clazz != null) {
String name = clazz.getName();
if (name.startsWith(“java.”) || name.startsWith(“javax.”) || name.startsWith(“android.”)) {
// Skip system classes, this just degrades performance
break;
}
// Starting with EventBus 2.2 we enforced methods to be public (might change with annotations again)
Method[] methods = clazz.getMethods();
for (Method method : methods) {
String methodName = method.getName();
if (methodName.startsWith(eventMethodName)) {
int modifiers = method.getModifiers();
if ((modifiers & Modifier.PUBLIC) != 0 && (modifiers & MODIFIERS_IGNORE) == 0) {
Class<?>[] parameterTypes = method.getParameterTypes();
if (parameterTypes.length == 1) {
String modifierString = methodName.substring(eventMethodName.length());
ThreadMode threadMode;
if (modifierString.length() == 0) {
threadMode = ThreadMode.PostThread;
} else if (modifierString.equals(“MainThread”)) {
threadMode = ThreadMode.MainThread;
} else if (modifierString.equals(“BackgroundThread”)) {
threadMode = ThreadMode.BackgroundThread;
} else if (modifierString.equals(“Async”)) {
threadMode = ThreadMode.Async;
} else {
if (skipMethodVerificationForClasses.containsKey(clazz)) {
continue;
} else {
throw new EventBusException(“Illegal onEvent method, check for typos: ” + method);
}
}
Class<?> eventType = parameterTypes[0];
methodKeyBuilder.setLength(0);
methodKeyBuilder.append(methodName);
methodKeyBuilder.append(’>’).append(eventType.getName());
String methodKey = methodKeyBuilder.toString();
if (eventTypesFound.add(methodKey)) {
// Only add if not already found in a sub class
subscriberMethods.add(new SubscriberMethod(method, threadMode, eventType));
}
}
} else if (!skipMethodVerificationForClasses.containsKey(clazz)) {
Log.d(EventBus.TAG, ”Skipping method (not public, static or abstract): ” + clazz + “.”
+ methodName);
}
}
}
clazz = clazz.getSuperclass();
}
if (subscriberMethods.isEmpty()) {
throw new EventBusException(“Subscriber ” + subscriberClass + “ has no public methods called ”
+ eventMethodName);
} else {
synchronized (methodCache) {
methodCache.put(key, subscriberMethods);
}
return subscriberMethods;
}
}

List<SubscriberMethod> findSubscriberMethods(Class<?> subscriberClass, String eventMethodName) {
        String key = subscriberClass.getName() + '.' + eventMethodName;
        List<SubscriberMethod> subscriberMethods;
        synchronized (methodCache) {
            subscriberMethods = methodCache.get(key);
        }
        if (subscriberMethods != null) {
            return subscriberMethods;
        }
        subscriberMethods = new ArrayList<SubscriberMethod>();
        Class<?> clazz = subscriberClass;
        HashSet<String> eventTypesFound = new HashSet<String>();
        StringBuilder methodKeyBuilder = new StringBuilder();
        while (clazz != null) {
            String name = clazz.getName();
            if (name.startsWith("java.") || name.startsWith("javax.") || name.startsWith("android.")) {
                // Skip system classes, this just degrades performance
                break;
            }

            // Starting with EventBus 2.2 we enforced methods to be public (might change with annotations again)
            Method[] methods = clazz.getMethods();
            for (Method method : methods) {
                String methodName = method.getName();
                if (methodName.startsWith(eventMethodName)) {
                    int modifiers = method.getModifiers();
                    if ((modifiers & Modifier.PUBLIC) != 0 && (modifiers & MODIFIERS_IGNORE) == 0) {
                        Class<?>[] parameterTypes = method.getParameterTypes();
                        if (parameterTypes.length == 1) {
                            String modifierString = methodName.substring(eventMethodName.length());
                            ThreadMode threadMode;
                            if (modifierString.length() == 0) {
                                threadMode = ThreadMode.PostThread;
                            } else if (modifierString.equals("MainThread")) {
                                threadMode = ThreadMode.MainThread;
                            } else if (modifierString.equals("BackgroundThread")) {
                                threadMode = ThreadMode.BackgroundThread;
                            } else if (modifierString.equals("Async")) {
                                threadMode = ThreadMode.Async;
                            } else {
                                if (skipMethodVerificationForClasses.containsKey(clazz)) {
                                    continue;
                                } else {
                                    throw new EventBusException("Illegal onEvent method, check for typos: " + method);
                                }
                            }
                            Class<?> eventType = parameterTypes[0];
                            methodKeyBuilder.setLength(0);
                            methodKeyBuilder.append(methodName);
                            methodKeyBuilder.append('>').append(eventType.getName());
                            String methodKey = methodKeyBuilder.toString();
                            if (eventTypesFound.add(methodKey)) {
                                // Only add if not already found in a sub class
                                subscriberMethods.add(new SubscriberMethod(method, threadMode, eventType));
                            }
                        }
                    } else if (!skipMethodVerificationForClasses.containsKey(clazz)) {
                        Log.d(EventBus.TAG, "Skipping method (not public, static or abstract): " + clazz + "."
                                + methodName);
                    }
                }
            }
            clazz = clazz.getSuperclass();
        }
        if (subscriberMethods.isEmpty()) {
            throw new EventBusException("Subscriber " + subscriberClass + " has no public methods called "
                    + eventMethodName);
        } else {
            synchronized (methodCache) {
                methodCache.put(key, subscriberMethods);
            }
            return subscriberMethods;
        }
    }

呵，代碼還真長；不過我們直接看核心部分：

22行：看到沒，clazz.getMethods();去得到所有的方法：

23-62行：就開始遍歷每一個方法了，去匹配封裝了。

25-29行：分別判斷了是否以onEvent開頭，是否是public且非static和abstract方法，是否是一個參數。如果都複合，才進入封裝的部分。

32-45行：也比較簡單，根據方法的後綴，來確定threadMode，threadMode是個枚舉類型：就四種情況。

最後在54行：將method, threadMode, eventType傳入構造了：new SubscriberMethod(method, threadMode, eventType)。添加到List，最終放回。

注意下63行：clazz = clazz.getSuperclass();可以看到，會掃描所有的父類，不僅僅是當前類。

繼續回到register:

[java] view plain copy

print?

for (SubscriberMethod subscriberMethod : subscriberMethods) {
subscribe(subscriber, subscriberMethod, sticky, priority);
}

for (SubscriberMethod subscriberMethod : subscriberMethods) {
            subscribe(subscriber, subscriberMethod, sticky, priority);
        }

for循環掃描到的方法，然後去調用suscribe方法。

[java] view plain copy

print?

// Must be called in synchronized block
private void subscribe(Object subscriber, SubscriberMethod subscriberMethod, boolean sticky, int priority) {
subscribed = true;
Class<?> eventType = subscriberMethod.eventType;
CopyOnWriteArrayList<Subscription> subscriptions = subscriptionsByEventType.get(eventType);
Subscription newSubscription = new Subscription(subscriber, subscriberMethod, priority);
if (subscriptions == null) {
subscriptions = new CopyOnWriteArrayList<Subscription>();
subscriptionsByEventType.put(eventType, subscriptions);
} else {
for (Subscription subscription : subscriptions) {
if (subscription.equals(newSubscription)) {
throw new EventBusException(“Subscriber ” + subscriber.getClass() + “ already registered to event ”
+ eventType);
}
}
}
// Starting with EventBus 2.2 we enforced methods to be public (might change with annotations again)
// subscriberMethod.method.setAccessible(true);
int size = subscriptions.size();
for (int i = 0; i <= size; i++) {
if (i == size || newSubscription.priority > subscriptions.get(i).priority) {
subscriptions.add(i, newSubscription);
break;
}
}
List<Class<?>> subscribedEvents = typesBySubscriber.get(subscriber);
if (subscribedEvents == null) {
subscribedEvents = new ArrayList<Class<?>>();
typesBySubscriber.put(subscriber, subscribedEvents);
}
subscribedEvents.add(eventType);
if (sticky) {
Object stickyEvent;
synchronized (stickyEvents) {
stickyEvent = stickyEvents.get(eventType);
}
if (stickyEvent != null) {
// If the subscriber is trying to abort the event, it will fail (event is not tracked in posting state)
// –> Strange corner case, which we don’t take care of here.
postToSubscription(newSubscription, stickyEvent, Looper.getMainLooper() == Looper.myLooper());
}
}
}

 // Must be called in synchronized block
    private void subscribe(Object subscriber, SubscriberMethod subscriberMethod, boolean sticky, int priority) {
        subscribed = true;
        Class<?> eventType = subscriberMethod.eventType;
        CopyOnWriteArrayList<Subscription> subscriptions = subscriptionsByEventType.get(eventType);
        Subscription newSubscription = new Subscription(subscriber, subscriberMethod, priority);
        if (subscriptions == null) {
            subscriptions = new CopyOnWriteArrayList<Subscription>();
            subscriptionsByEventType.put(eventType, subscriptions);
        } else {
            for (Subscription subscription : subscriptions) {
                if (subscription.equals(newSubscription)) {
                    throw new EventBusException("Subscriber " + subscriber.getClass() + " already registered to event "
                            + eventType);
                }
            }
        }

        // Starting with EventBus 2.2 we enforced methods to be public (might change with annotations again)
        // subscriberMethod.method.setAccessible(true);

        int size = subscriptions.size();
        for (int i = 0; i <= size; i++) {
            if (i == size || newSubscription.priority > subscriptions.get(i).priority) {
                subscriptions.add(i, newSubscription);
                break;
            }
        }

        List<Class<?>> subscribedEvents = typesBySubscriber.get(subscriber);
        if (subscribedEvents == null) {
            subscribedEvents = new ArrayList<Class<?>>();
            typesBySubscriber.put(subscriber, subscribedEvents);
        }
        subscribedEvents.add(eventType);

        if (sticky) {
            Object stickyEvent;
            synchronized (stickyEvents) {
                stickyEvent = stickyEvents.get(eventType);
            }
            if (stickyEvent != null) {
                // If the subscriber is trying to abort the event, it will fail (event is not tracked in posting state)
                // --> Strange corner case, which we don't take care of here.
                postToSubscription(newSubscription, stickyEvent, Looper.getMainLooper() == Looper.myLooper());
            }
        }
    }

我們的subscriberMethod中保存了method, threadMode, eventType，上面已經說了；

4-17行：根據subscriberMethod.eventType，去subscriptionsByEventType去查找一個CopyOnWriteArrayList<Subscription> ，如果沒有則創建。

順便把我們的傳入的參數封裝成了一個：Subscription（subscriber, subscriberMethod, priority）；

這裏的subscriptionsByEventType是個Map，key：eventType ； value：CopyOnWriteArrayList<Subscription> ；這個Map其實就是EventBus存儲方法的地方，一定要記住！

22-28行：實際上，就是添加newSubscription；並且是按照優先級添加的。可以看到，優先級越高，會插到在當前List的前面。

30-35行：根據subscriber存儲它所有的eventType ；依然是map；key：subscriber ，value：List<eventType> ;知道就行，非核心代碼，主要用於isRegister的判斷。

37-47行：判斷sticky；如果爲true，從stickyEvents中根據eventType去查找有沒有stickyEvent，如果有則立即發佈去執行。stickyEvent其實就是我們post時的參數。

postToSubscription這個方法，我們在post的時候會介紹。

到此，我們register就介紹完了。

你只要記得一件事：掃描了所有的方法，把匹配的方法最終保存在subscriptionsByEventType（Map，key：eventType ； value：CopyOnWriteArrayList<Subscription> ）中；

eventType是我們方法參數的Class，Subscription中則保存着subscriber, subscriberMethod（method, threadMode, eventType）, priority；包含了執行改方法所需的一切。

3、post

register完畢，知道了EventBus如何存儲我們的方法了，下面看看post它又是如何調用我們的方法的。

再看源碼之前，我們猜測下：register時，把方法存在subscriptionsByEventType；那麼post肯定會去subscriptionsByEventType去取方法，然後調用。

下面看源碼：

[java] view plain copy

print?

/** 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) {
return;
} else {
postingState.isMainThread = Looper.getMainLooper() == Looper.myLooper();
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;
}
}
}

 /** 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) {
            return;
        } else {
            postingState.isMainThread = Looper.getMainLooper() == Looper.myLooper();
            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;
            }
        }
    }

currentPostingThreadState是一個ThreadLocal類型的，裏面存儲了PostingThreadState；PostingThreadState包含了一個eventQueue和一些標誌位。

[java] view plain copy

print?

private final ThreadLocal<PostingThreadState> currentPostingThreadState = new ThreadLocal<PostingThreadState>() {
@Override
protected PostingThreadState initialValue() {
return new PostingThreadState();
}
}

 private final ThreadLocal<PostingThreadState> currentPostingThreadState = new ThreadLocal<PostingThreadState>() {
        @Override
        protected PostingThreadState initialValue() {
            return new PostingThreadState();
        }
    }

把我們傳入的event，保存到了當前線程中的一個變量PostingThreadState的eventQueue中。

10行：判斷當前是否是UI線程。

16-18行：遍歷隊列中的所有的event，調用postSingleEvent（eventQueue.remove(0), postingState）方法。

這裏大家會不會有疑問，每次post都會去調用整個隊列麼，那麼不會造成方法多次調用麼？

可以看到第7-8行，有個判斷，就是防止該問題的，isPosting=true了，就不會往下走了。

下面看postSingleEvent

[java] view plain copy

print?

private void postSingleEvent(Object event, PostingThreadState postingState) throws Error {
Class<? extends Object> eventClass = event.getClass();
List<Class<?>> eventTypes = findEventTypes(eventClass);
boolean subscriptionFound = false;
int countTypes = eventTypes.size();
for (int h = 0; h < countTypes; h++) {
Class<?> clazz = eventTypes.get(h);
CopyOnWriteArrayList<Subscription> subscriptions;
synchronized (this) {
subscriptions = subscriptionsByEventType.get(clazz);
}
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;
}
}
subscriptionFound = true;
}
}
if (!subscriptionFound) {
Log.d(TAG, ”No subscribers registered for event ” + eventClass);
if (eventClass != NoSubscriberEvent.class && eventClass != SubscriberExceptionEvent.class) {
post(new NoSubscriberEvent(this, event));
}
}
}

private void postSingleEvent(Object event, PostingThreadState postingState) throws Error {
        Class<? extends Object> eventClass = event.getClass();
        List<Class<?>> eventTypes = findEventTypes(eventClass);
        boolean subscriptionFound = false;
        int countTypes = eventTypes.size();
        for (int h = 0; h < countTypes; h++) {
            Class<?> clazz = eventTypes.get(h);
            CopyOnWriteArrayList<Subscription> subscriptions;
            synchronized (this) {
                subscriptions = subscriptionsByEventType.get(clazz);
            }
            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;
                    }
                }
                subscriptionFound = true;
            }
        }
        if (!subscriptionFound) {
            Log.d(TAG, "No subscribers registered for event " + eventClass);
            if (eventClass != NoSubscriberEvent.class && eventClass != SubscriberExceptionEvent.class) {
                post(new NoSubscriberEvent(this, event));
            }
        }
    }

將我們的event，即post傳入的實參；以及postingState傳入到postSingleEvent中。

2-3行：根據event的Class，去得到一個List<Class<?>>；其實就是得到event當前對象的Class，以及父類和接口的Class類型；主要用於匹配，比如你傳入Dog extends Dog，他會把Animal也裝到該List中。

6-31行：遍歷所有的Class，到subscriptionsByEventType去查找subscriptions；哈哈，熟不熟悉，還記得我們register裏面把方法存哪了不？

是不是就是這個Map;

12-30行：遍歷每個subscription,依次去調用postToSubscription(subscription, event, postingState.isMainThread);
這個方法就是去反射執行方法了，大家還記得在register，if(sticky)時，也會去執行這個方法。

下面看它如何反射執行：

[java] view plain copy

print?

private void postToSubscription(Subscription subscription, Object event, boolean isMainThread) {
switch (subscription.subscriberMethod.threadMode) {
case PostThread:
invokeSubscriber(subscription, event);
break;
case MainThread:
if (isMainThread) {
invokeSubscriber(subscription, event);
} else {
mainThreadPoster.enqueue(subscription, event);
}
break;
case BackgroundThread:
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);
}
}

private void postToSubscription(Subscription subscription, Object event, boolean isMainThread) {
        switch (subscription.subscriberMethod.threadMode) {
        case PostThread:
            invokeSubscriber(subscription, event);
            break;
        case MainThread:
            if (isMainThread) {
                invokeSubscriber(subscription, event);
            } else {
                mainThreadPoster.enqueue(subscription, event);
            }
            break;
        case BackgroundThread:
            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);
        }
    }

前面已經說過subscription包含了所有執行需要的東西，大致有:subscriber, subscriberMethod（method, threadMode, eventType）, priority；

那麼這個方法：第一步根據threadMode去判斷應該在哪個線程去執行該方法；
case PostThread:

[java] view plain copy

print?

void invokeSubscriber(Subscription subscription, Object event) throws Error {
subscription.subscriberMethod.method.invoke(subscription.subscriber, event);
｝

  void invokeSubscriber(Subscription subscription, Object event) throws Error {
            subscription.subscriberMethod.method.invoke(subscription.subscriber, event);
  ｝

直接反射調用；也就是說在當前的線程直接調用該方法；

case MainThread:

首先去判斷當前如果是UI線程，則直接調用；否則： mainThreadPoster.enqueue(subscription, event);把當前的方法加入到隊列，然後直接通過handler去發送一個消息，在handler的handleMessage中，去執行我們的方法。說白了就是通過Handler去發送消息，然後執行的。

case BackgroundThread:

如果當前非UI線程，則直接調用；如果是UI線程，則將任務加入到後臺的一個隊列，最終由Eventbus中的一個線程池去調用

executorService = Executors.newCachedThreadPool();。

case Async:將任務加入到後臺的一個隊列，最終由Eventbus中的一個線程池去調用；線程池與BackgroundThread用的是同一個。

這麼說BackgroundThread和Async有什麼區別呢？

BackgroundThread中的任務，一個接着一個去調用，中間使用了一個布爾型變量handlerActive進行的控制。

Async則會動態控制併發。

到此，我們完整的源碼分析就結束了，總結一下：register會把當前類中匹配的方法，存入一個map，而post會根據實參去map查找進行反射調用。分析這麼久，一句話就說完了~~

其實不用發佈者，訂閱者，事件，總線這幾個詞或許更好理解，以後大家問了EventBus，可以說，就是在一個單例內部維持着一個map對象存儲了一堆的方法；post無非就是根據參數去查找方法，進行反射調用。

4、其餘方法

介紹了register和post；大家獲取還能想到一個詞sticky，在register中，如何sticky爲true，會去stickyEvents去查找事件，然後立即去post；

那麼這個stickyEvents何時進行保存事件呢？

其實evevntbus中，除了post發佈事件，還有一個方法也可以：

[java] view plain copy

print?

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);
}

 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);
    }

和post功能類似，但是會把方法存儲到stickyEvents中去；

大家再去看看EventBus中所有的public方法，無非都是一些狀態判斷，獲取事件，移除事件的方法；沒什麼好介紹的，基本見名知意。

好了，到此我們的源碼解析就結束了，希望大家不僅能夠了解這些優秀框架的內部機理，更能夠體會到這些框架的很多細節之處，併發的處理，很多地方，爲什麼它這麼做等等。

我建了一個QQ羣，方便大家交流。羣號：55032675

———————————————————————————————————-

博主部分視頻已經上線，如果你不喜歡枯燥的文本，請猛戳（初錄，期待您的支持）：

1、高仿微信5.2.1主界面及消息提醒

2、高仿QQ5.0側滑

3、Android 智能機器人“小慕”的實現

Android EventBus源碼解析帶你深入理解EventBus

1、概述

2、register

3、post

4、其餘方法

Android應對進程被殺死--Service（二）

Android 使用mina框架搭建socket客戶端，進行與服務器端通信

文件夾的創建，刪除，重命名，怎麼同時創建多個文件夾

File文件的屬性獲取

關於經典藍牙和低功耗藍牙的區別

https://yachay.unat.edu.pe/blog/index.php?comment_area=format_blog&comment_component=blog&comment_co

linux以太網驅動總結

Android EventBus源碼解析 帶你深入理解EventBus

1、概述

2、register

3、post

4、其餘方法

Android EventBus源碼解析帶你深入理解EventBus