仿EventBus做一个简单的基于订阅发布的事件总线

一、概述

　　在上一节分析了EventBus的源代码。本节仿照EventBus自己做一个事件总线框架，去掉了一些代码，只保留了核心框架，旨在梳理框架的框架原理，加深对框架流程的理解。

　　在贴出源代码之前先把这个自定义的EventBus的功能介绍一下。核心流程还是三个，注册、发布、取消注册（未写AnnotationProcessor部分，如果有需要大家可以自己实现），源码中的类绝大部分分仿照了EventBus原有的类名，只是类里面的内容做了简化调整。如：EventBus类只抽离了、post、register、unregister、subscribe方法等。

　　完整源代码下载地址

　　下面贴出library结构

　　

 

 自己实现的框架其用法和EventBus还是一样的，只是不能发送黏性事假和定义事件的优先级，使用实例代码如下：

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public class MainActivity extends AppCompatActivity {     private Button btn;     private TextView tv;       @Override     protected void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.activity_main);         /**          * 注册观察者对象          */         EventBus.getDefault().register(this);         btn = findViewById(R.id.main_btn);         tv = findViewById(R.id.main_tv);         btn.setOnClickListener(new View.OnClickListener() {             @Override             public void onClick(View v) {                 toPost();             }         });       }       /**      * 用于接收post发送过来的事件      *      * @param event 具体的事件主体      */     @Subscribe     public void onMessageEvent(MessageEvent event) {         switch (event.getArg1()) {             case 0:                 tv.setText("接收小消息为：" + event.getMsg());                 break;           }     }       @Override     protected void onDestroy() {         super.onDestroy();         /**          * 取消订阅          */         EventBus.getDefault().unRegister(this);     }       /**      * 发送消息      */     public void toPost() {         MessageEvent event = new MessageEvent();         event.setArg1(0);         event.setMsg("杨洛峋小宝宝来了");         EventBus.getDefault().post(event);     }   }

　

二、源码介绍以及源码截图

　　下面提出关键源代码

　　EventBus.getDefault().register(subscriber)

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/**    * 注册    * 订阅方法    *    * @param subscriber    */   public void register(Object subscriber) {       Class clazz = subscriber.getClass();       List<SubscriberMethod> subscriberMethods = SubscriberMethodFinder.findSubscriberMethods(clazz);       if (subscriberMethods != null && subscriberMethods.size() > 0) {           for (SubscriberMethod subscriberMethod : subscriberMethods) {               subscribe(subscriber, subscriberMethod);           }       }   }     /**    * 真正的订阅    *    * @param subscriber    * @param subscriberMethod    */   private void subscribe(Object subscriber, SubscriberMethod subscriberMethod) {       Class eventType = subscriberMethod.getEventType();       Subscription newSubscription = new Subscription(subscriber, subscriberMethod);       CopyOnWriteArrayList<Subscription> subscriptions = subscriptionsByEventType.get(eventType);       if (subscriptions == null) {           subscriptions = new CopyOnWriteArrayList<>();           subscriptionsByEventType.put(eventType, subscriptions);       }       int size = subscriptions.size();       for (int i = 0; i <= size; i++) {           if (i == size) {               //向订阅集合中加入订阅               subscriptions.add(i, newSubscription);               break;           }       }         List<Class<?>> subscribedEvents = typesBySubscriber.get(subscriber);       if (subscribedEvents == null) {           subscribedEvents = new ArrayList<>();           typesBySubscriber.put(subscriber, subscribedEvents);       }       subscribedEvents.add(eventType);     }

　　EventBus.getDefault().post(eventObj)

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/**     * 发送事件方法     *     * @param eventObj     */    public void post(Object eventObj) {        PostingThreadState postingThreadState = currentPostingThreadState.get();        List<Object> queue = postingThreadState.getEventQueue();        queue.add(eventObj);        postingThreadState.setMainThread(isMainThread());        //缺少一个发送事件的线程        Class<?> clazz = eventObj.getClass();        List<Subscription> subscriptions = subscriptionsByEventType.get(clazz);        if (subscriptions != null) {            //循环遍历Subscriptions，            for (Subscription subscription : subscriptions) {                //分发事件                postToSubscription(subscription, eventObj, postingThreadState);              }        }      }      /**     * 返回true为主线程，否则为子线程     *     * @return     */    private boolean isMainThread() {        return Looper.myLooper() == Looper.getMainLooper();    }      /**     * 对事件进行分发     *     * @param subscription     * @param eventTypeObj     */    private void postToSubscription(Subscription subscription, Object eventTypeObj, PostingThreadState postingThreadState) {        switch (subscription.getSubscriberMethod().getThreadMode()) {            case POSITION:                invokeSubscriber(subscription, eventTypeObj);                break;            case MAIN:                if (isMainThread()) {                    invokeSubscriber(subscription, eventTypeObj);                } else {                    mainThreadHandlerPoster.enqueue(subscription, eventTypeObj);                }                break;            case MAIN_ORDERD:                if (mainThreadHandlerPoster != null) {                    mainThreadHandlerPoster.enqueue(subscription, eventTypeObj);                } else {                    invokeSubscriber(subscription, eventTypeObj);                }                break;            case BACKGROUND:                if (backgroundPoster != null) {                    backgroundPoster.enqueue(subscription, eventTypeObj);                } else {                    invokeSubscriber(subscription, eventTypeObj);                }                break;            case ASYNC:                asyncPoster.enqueue(subscription, eventTypeObj);                break;        }    }      /**     * 执行事件的具体方法     *     * @param subscription     * @param eventTypeObj     */    public void invokeSubscriber(Subscription subscription, Object eventTypeObj) {        try {            subscription.getSubscriberMethod().getMethod().setAccessible(true);            subscription.getSubscriberMethod().getMethod().invoke(subscription.getSubscriber(), eventTypeObj);        } catch (IllegalAccessException e) {            e.printStackTrace();        } catch (InvocationTargetException e) {            e.printStackTrace();        }    }

　　EventBus.getDefault().unRegister(subscriber)

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/**     * 取消注册方法     * 取消注册其实就清除两个 集合就行了，一个是Subscriptions集合，一个是typesBySubscriber集合     *     * @param subscriber     */    public void unRegister(Object subscriber) {        List<Class<?>> eventTypes = typesBySubscriber.get(subscriber);        if (eventTypes != null) {            for (Class<?> clazz : eventTypes) {                CopyOnWriteArrayList<Subscription> subscriptions = subscriptionsByEventType.get(clazz);                for (Subscription subscription : subscriptions) {                    if (subscriber == subscription.getSubscriber()) {                        subscriptions.remove(subscription);                    }                }            }            typesBySubscriber.remove(subscriber);        }      }

　　完整的源代码我发布到了github上欢迎大家下载，地址如下：myeventbuslib