美女黄18以下禁止观看,亚洲av成人一区在线,人妻中文字幕不卡精品

Android事件總線（二）EventBus3.0源碼解析

1.構(gòu)造函數(shù)

當(dāng)我們要調(diào)用EventBus的功能時(shí)，比如注冊(cè)或者發(fā)送事件，總會(huì)調(diào)用EventBus.getDefault()來(lái)獲取EventBus實(shí)例：

public static EventBus getDefault() {
    if (defaultInstance == null) {
        synchronized (EventBus.class) {
            if (defaultInstance == null) {
                defaultInstance = new EventBus();
            }
        }
    }
    return defaultInstance;
}

View Code

很明顯這是一個(gè)單例模式，采用了雙重檢查模式（DCL）。
接下來(lái)看看new EventBus()做了什么：

public EventBus() {
      this(DEFAULT_BUILDER);
  }

View Code

這里DEFAULT_BUILDER是默認(rèn)的EventBusBuilder，用來(lái)構(gòu)造EventBus：

private static final EventBusBuilder DEFAULT_BUILDER = new EventBusBuilder();

this調(diào)用了EventBus另一個(gè)構(gòu)造函數(shù)：

EventBus(EventBusBuilder builder) {
    subscriptionsByEventType = new HashMap<>();
    typesBySubscriber = new HashMap<>();
    stickyEvents = new ConcurrentHashMap<>();
    mainThreadPoster = new HandlerPoster(this, Looper.getMainLooper(), 10);
    backgroundPoster = new BackgroundPoster(this);
    asyncPoster = new AsyncPoster(this);
    indexCount = builder.subscriberInfoIndexes != null ? builder.subscriberInfoIndexes.size() : 0;
    subscriberMethodFinder = new SubscriberMethodFinder(builder.subscriberInfoIndexes,
            builder.strictMethodVerification, builder.ignoreGeneratedIndex);
    logSubscriberExceptions = builder.logSubscriberExceptions;
    logNoSubscriberMessages = builder.logNoSubscriberMessages;
    sendSubscriberExceptionEvent = builder.sendSubscriberExceptionEvent;
    sendNoSubscriberEvent = builder.sendNoSubscriberEvent;
    throwSubscriberException = builder.throwSubscriberException;
    eventInheritance = builder.eventInheritance;
    executorService = builder.executorService;
}

View Code

2.訂閱者注冊(cè)

獲取到EventBus后，便可以將訂閱者注冊(cè)到EventBus中，下面來(lái)看一下register方法：

public void register(Object subscriber) {
     Class<?> subscriberClass = subscriber.getClass();
 // 用 subscriberMethodFinder 提供的方法，找到在 subscriber 這個(gè)類里面訂閱的內(nèi)容。
     List<SubscriberMethod> subscriberMethods = subscriberMethodFinder.findSubscriberMethods(subscriberClass);
     synchronized (this) {
         for (SubscriberMethod subscriberMethod : subscriberMethods) {
             subscribe(subscriber, subscriberMethod);
         }
     }
 }

View Code

查找訂閱方法

findSubscriberMethods找出一個(gè)SubscriberMethod的集合，也就是傳進(jìn)來(lái)的訂閱者所有的訂閱的方法，接下來(lái)遍歷訂閱者的訂閱方法來(lái)完成訂閱者的訂閱操作。對(duì)于SubscriberMethod（訂閱方法）類中，主要就是用保存訂閱方法的Method對(duì)象、線程模式、事件類型、優(yōu)先級(jí)、是否是粘性事件等屬性。下面就來(lái)看一下findSubscriberMethods方法：

List<SubscriberMethod> findSubscriberMethods(Class<?> subscriberClass) {
       //從緩存中獲取SubscriberMethod集合
       List<SubscriberMethod> subscriberMethods = METHOD_CACHE.get(subscriberClass);
       if (subscriberMethods != null) {
           return subscriberMethods;
       }
       //ignoreGeneratedIndex屬性表示是否忽略注解器生成的MyEventBusIndex
       if (ignoreGeneratedIndex) {
        //通過(guò)反射獲取subscriberMethods
           subscriberMethods = findUsingReflection(subscriberClass);
       } else {
           subscriberMethods = findUsingInfo(subscriberClass);
       }
       //在獲得subscriberMethods以后，如果訂閱者中不存在@Subscribe注解并且為public的訂閱方法，則會(huì)拋出異常。
       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;
       }
   }

View Code

首先從緩存中查找，如果找到了就立馬返回。如果緩存中沒有的話，則根據(jù) ignoreGeneratedIndex 選擇如何查找訂閱方法，ignoreGeneratedIndex屬性表示是否忽略注解器生成的MyEventBusIndex。不了解MyEventBusIndex的同學(xué)可以查看【Bugly干貨分享】老司機(jī)教你 “飆” EventBus 3這篇文章。最后，找到訂閱方法后，放入緩存，以免下次繼續(xù)查找。ignoreGeneratedIndex 默認(rèn)就是false，可以通過(guò)EventBusBuilder來(lái)設(shè)置它的值。我們?cè)陧?xiàng)目中經(jīng)常通過(guò)EventBus單例模式來(lái)獲取默認(rèn)的EventBus對(duì)象，也就是ignoreGeneratedIndex為false的情況，這種情況調(diào)用了findUsingInfo方法：

private List<SubscriberMethod> findUsingInfo(Class<?> subscriberClass) {
    FindState findState = prepareFindState();
    findState.initForSubscriber(subscriberClass);
    while (findState.clazz != null) {
     //獲取訂閱者信息，沒有配置MyEventBusIndex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 {
            //通過(guò)反射來(lái)查找訂閱方法
            findUsingReflectionInSingleClass(findState);
        }
        findState.moveToSuperclass();
    }
    return getMethodsAndRelease(findState);
}

View Code

通過(guò)getSubscriberInfo方法來(lái)獲取訂閱者信息。在我們開始查找訂閱方法的時(shí)候并沒有忽略注解器為我們生成的索引MyEventBusIndex，如果我們通過(guò)EventBusBuilder配置了MyEventBusIndex，便會(huì)獲取到subscriberInfo，調(diào)用subscriberInfo的getSubscriberMethods方法便可以得到訂閱方法相關(guān)的信息，這個(gè)時(shí)候就不在需要通過(guò)注解進(jìn)行獲取訂閱方法。如果沒有配置MyEventBusIndex，便會(huì)執(zhí)行findUsingReflectionInSingleClass方法，將訂閱方法保存到findState中。最后再通過(guò)getMethodsAndRelease方法對(duì)findState做回收處理并反回訂閱方法的List集合。
對(duì)于MyEventBusIndex的配置它是一個(gè)可選項(xiàng)，所以在這里就不在進(jìn)行詳細(xì)的介紹，下面就來(lái)看一下findUsingReflectionInSingleClass的執(zhí)行過(guò)程：

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");
        }
    }
}

View Code

在這里主要是使用了Java的反射和對(duì)注解的解析。首先通過(guò)反射來(lái)獲取訂閱者中所有的方法。并根據(jù)方法的類型，參數(shù)和注解來(lái)找到訂閱方法。找到訂閱方法后將訂閱方法相關(guān)信息保存到FindState當(dāng)中。

訂閱者的注冊(cè)過(guò)程

在查找完所有的訂閱方法以后便開始對(duì)所有的訂閱方法進(jìn)行注冊(cè)：

 private void subscribe(Object subscriber, SubscriberMethod subscriberMethod) {
        Class<?> eventType = subscriberMethod.eventType;
          //根據(jù)訂閱者和訂閱方法構(gòu)造一個(gè)訂閱事件
        Subscription newSubscription = new Subscription(subscriber, subscriberMethod);
          //獲取當(dāng)前訂閱事件中Subscription的List集合
        CopyOnWriteArrayList<Subscription> subscriptions = subscriptionsByEventType.get(eventType);
         //該事件對(duì)應(yīng)的Subscription的List集合不存在，則重新創(chuàng)建并保存在subscriptionsByEventType中
        if (subscriptions == null) {
            subscriptions = new CopyOnWriteArrayList<>();
            subscriptionsByEventType.put(eventType, subscriptions);
        } else {
        //訂閱者已經(jīng)注冊(cè)則拋出EventBusException
            if (subscriptions.contains(newSubscription)) {
                throw new EventBusException("Subscriber " + subscriber.getClass() + " already registered to event "
                        + eventType);
            }
        }
//遍歷訂閱事件，找到比subscriptions中訂閱事件小的位置，然后插進(jìn)去
        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;
            }
        }
         //通過(guò)訂閱者獲取該訂閱者所訂閱事件的集合
        List<Class<?>> subscribedEvents = typesBySubscriber.get(subscriber);
        if (subscribedEvents == null) {
            subscribedEvents = new ArrayList<>();
            typesBySubscriber.put(subscriber, subscribedEvents);
        }
          //將當(dāng)前的訂閱事件添加到subscribedEvents中
        subscribedEvents.add(eventType);
        if (subscriberMethod.sticky) {
            if (eventInheritance) {
            //粘性事件的處理
                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);
            }
        }
    }

View Code

訂閱的代碼主要就做了兩件事，第一件事是將我們的訂閱方法和訂閱者封裝到subscriptionsByEventType和typesBySubscriber中，subscriptionsByEventType是我們投遞訂閱事件的時(shí)候，就是根據(jù)我們的EventType找到我們的訂閱事件，從而去分發(fā)事件，處理事件的；typesBySubscriber在調(diào)用unregister(this)的時(shí)候，根據(jù)訂閱者找到EventType，又根據(jù)EventType找到訂閱事件，從而對(duì)訂閱者進(jìn)行解綁。第二件事，如果是粘性事件的話，就立馬投遞、執(zhí)行。

3.事件的發(fā)送

在獲取到EventBus對(duì)象以后，可以通過(guò)post方法來(lái)進(jìn)行對(duì)事件的提交：

public void post(Object event) {
     //PostingThreadState保存著事件隊(duì)列和線程狀態(tài)信息
      PostingThreadState postingState = currentPostingThreadState.get();
     //獲取事件隊(duì)列，并將當(dāng)前事插入到事件隊(duì)列中
      List<Object> eventQueue = postingState.eventQueue;
      eventQueue.add(event);

      if (!postingState.isPosting) {
          postingState.isMainThread = Looper.getMainLooper() == Looper.myLooper();
          postingState.isPosting = true;
          if (postingState.canceled) {
              throw new EventBusException("Internal error. Abort state was not reset");
          }
          try {
            //處理隊(duì)列中的所有事件
              while (!eventQueue.isEmpty()) {
                  postSingleEvent(eventQueue.remove(0), postingState);
              }
          } finally {
              postingState.isPosting = false;
              postingState.isMainThread = false;
          }
      }
  }

View Code

首先從PostingThreadState對(duì)象中取出事件隊(duì)列，然后再將當(dāng)前的事件插入到事件隊(duì)列當(dāng)中。最后將隊(duì)列中的事件依次交由postSingleEvent方法進(jìn)行處理，并移除該事件。來(lái)看看postSingleEvent方法里做了什么：

private void postSingleEvent(Object event, PostingThreadState postingState) throws Error {
       Class<?> eventClass = event.getClass();
       boolean subscriptionFound = false;
       //eventInheritance表示是否向上查找事件的父類,默認(rèn)為true
       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);
       }
         //找不到該事件時(shí)的異常處理
       if (!subscriptionFound) {
           if (logNoSubscriberMessages) {
               Log.d(TAG, "No subscribers registered for event " + eventClass);
           }
           if (sendNoSubscriberEvent && eventClass != NoSubscriberEvent.class &&
                   eventClass != SubscriberExceptionEvent.class) {
               post(new NoSubscriberEvent(this, event));
           }
       }
   }

View Code

eventInheritance表示是否向上查找事件的父類,它的默認(rèn)值為true，可以通過(guò)在EventBusBuilder中來(lái)進(jìn)行配置。當(dāng)eventInheritance為true時(shí)，則通過(guò)lookupAllEventTypes找到所有的父類事件并存在List中，然后通過(guò)postSingleEventForEventType方法對(duì)事件逐一處理，接下來(lái)看看postSingleEventForEventType方法：

private boolean postSingleEventForEventType(Object event, PostingThreadState postingState, Class<?> eventClass) {
      CopyOnWriteArrayList<Subscription> subscriptions;
         //取出該事件對(duì)應(yīng)的Subscription集合
      synchronized (this) {
          subscriptions = subscriptionsByEventType.get(eventClass);
      }
      if (subscriptions != null && !subscriptions.isEmpty()) {
      //將該事件的event和對(duì)應(yīng)的Subscription中的信息（包擴(kuò)訂閱者類和訂閱方法）傳遞給postingState
          for (Subscription subscription : subscriptions) {
              postingState.event = event;
              postingState.subscription = subscription;
              boolean aborted = false;
              try {
                 //對(duì)事件進(jìn)行處理
                  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;
  }

View Code

同步取出該事件對(duì)應(yīng)的Subscription集合并遍歷該集合將事件event和對(duì)應(yīng)Subscription傳遞給postingState并調(diào)用postToSubscription方法對(duì)事件進(jìn)行處理，接下來(lái)看看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 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);
    }
}

View Code

取出訂閱方法的線程模式，之后根據(jù)線程模式來(lái)分別處理。舉個(gè)例子，如果線程模式是MAIN，提交事件的線程是主線程的話則通過(guò)反射，直接運(yùn)行訂閱的方法，如果不是主線程，我們需要mainThreadPoster將我們的訂閱事件入隊(duì)列，mainThreadPoster是HandlerPoster類型的繼承自Handler，通過(guò)Handler將訂閱方法切換到主線程執(zhí)行。

4.訂閱者取消注冊(cè)

public synchronized void unregister(Object subscriber) {
    List<Class<?>> subscribedTypes = typesBySubscriber.get(subscriber);
    if (subscribedTypes != null) {
        for (Class<?> eventType : subscribedTypes) {
            unsubscribeByEventType(subscriber, eventType);
        }
        typesBySubscriber.remove(subscriber);
    } else {
        Log.w(TAG, "Subscriber to unregister was not registered before: " + subscriber.getClass());
    }
}

View Code

typesBySubscriber我們?cè)谟嗛喺咦?cè)的過(guò)程中講到過(guò)這個(gè)屬性，他根據(jù)訂閱者找到EventType，然后根據(jù)EventType和訂閱者來(lái)得到訂閱事件來(lái)對(duì)訂閱者進(jìn)行解綁。

5.核心架構(gòu)與利弊

核心架構(gòu)

從EventBus作者提供的圖我們可以看到EventBus的核心架構(gòu)，其實(shí)就是基于觀察者模式來(lái)實(shí)現(xiàn)的，關(guān)于觀察者模式可以查看設(shè)計(jì)模式（五）觀察者模式這篇文章。

利與弊

EventBus好處比較明顯，它能夠解耦和，將業(yè)務(wù)和視圖分離，代碼實(shí)現(xiàn)比較容易。而且3.0后，我們可以通過(guò)apt預(yù)編譯找到訂閱者，避免了運(yùn)行期間的反射處理解析，大大提高了效率。當(dāng)然EventBus也會(huì)帶來(lái)一些隱患和弊端，如果濫用的話會(huì)導(dǎo)致邏輯的分散并造成維護(hù)起來(lái)的困難。另外大量采用EventBus代碼的可讀性也會(huì)變差。

參考資料
EventBus3.0源碼
 EventBus3.0 源碼解析
 EventBus 利弊與源碼解析
 EventBus3.0源碼解讀
 【Bugly干貨分享】老司機(jī)教你 “飆” EventBus 3

posted on 2016-10-27 23:46 安卓筆記俠閱讀(556) 評(píng)論(0) 收藏舉報(bào)

刷新頁(yè)面返回頂部

安卓筆記俠

導(dǎo)航

Android事件總線（二）EventBus3.0源碼解析

1.構(gòu)造函數(shù)

2.訂閱者注冊(cè)

查找訂閱方法

訂閱者的注冊(cè)過(guò)程

3.事件的發(fā)送

4.訂閱者取消注冊(cè)

5.核心架構(gòu)與利弊

核心架構(gòu)

利與弊