EventBus框架分析&实现

在EventBus使用详解及组件之间通信中我们已经介绍了EventBus的使用及注册,接受消息,销毁等流程，下面我们就分析一下EventBus是如何实现

注册	Eventbus.getDefault().register(this);
发送消息	Eventbus.getDefault().post(new MessageBean("meg", "test"));
接收消息	@Subscribe(threadMode = ThreadMode.Async) public void receive(MessageBean messageBean ) { }

实现思路:


 (1).定义注解 Subscribe

@Retention(RetentionPolicy.RUNTIME) public @interface Subscribe { ThreadMode threadMode() default ThreadMode.PostThread; }

(2).注册Activity

register

private static Eventbus instance = new Eventbus(); private ExecutorService executorService; //存放对应的activity及 线程类型,接受参数,及对应的方法 private Map<Object, List<SubscribleMethod>> cacheMap; private Handler handler; public static Eventbus getDefault() { return instance; } private Eventbus( ) { this.cacheMap = new HashMap<>(); executorService = Executors.newCachedThreadPool(); handler = new Handler(Looper.getMainLooper()); } /** * 注册 * @param activity */ public void register(Object activity) { Class<?> clazz = activity.getClass(); List<SubscribleMethod> list = cacheMap.get(activity);// 如果已经注册 就不需要注册 if (list == null) { list = getSubscribleMethods(activity); cacheMap.put(activity, list); } } /** * 寻找能够接受事件的方法 * * @param activity * @return */ private List<SubscribleMethod> getSubscribleMethods(Object activity) { List<SubscribleMethod> list = new ArrayList<>(); Class clazz = activity.getClass(); /** * BaseActivity ---->Activity(找 ) */ while (clazz != null) { String name = clazz.getName(); if (name.startsWith("java.") || name.startsWith("javax.") || name.startsWith("android.")) { break; } Method[] methods = clazz.getDeclaredMethods(); for (Method method : methods) { Subscribe subscribe = method.getAnnotation(Subscribe.class); if (subscribe == null) { continue; } Class[] paratems = method.getParameterTypes(); if (paratems.length != 1) { throw new RuntimeException("eventbus只能接收到一个参数"); } // ThreadMode threadMode = subscribe.threadMode(); SubscribleMethod subscribleMethod = new SubscribleMethod(method , threadMode, paratems[0]); list.add(subscribleMethod); } clazz = clazz.getSuperclass(); } return list; }

(3).接受消息

@Subscribe(threadMode = ThreadMode.Async) public void receive(MessageBean messageBean ) { }

(4).发送消息

/** * 通知 * @param msg */ public void post(final Object msg) { /** * 遍历 找到 注册的activity */ Set<Object> set = cacheMap.keySet(); Iterator iterator = set.iterator(); while (iterator.hasNext()) { final Object activity = iterator.next(); List<SubscribleMethod> list = cacheMap.get(activity); for (final SubscribleMethod subscribleMethod : list) { // 判断 这个方法是否应该接受事件 if (subscribleMethod.getEventType().isAssignableFrom(msg.getClass())) { switch (subscribleMethod.getThreadMode()) { // 接受方法在子线程执行的情况 case Async: if (Looper.myLooper() == Looper.getMainLooper()) { // post方法 执行在子线程 executorService.execute(new Runnable() { @Override public void run() { invoke(subscribleMethod, activity, msg); } }); } else { // post方法 执行在子线程 invoke(subscribleMethod, activity, msg); } break; // 接受方法在主线程执行的情况 case MainThread: if (Looper.myLooper() == Looper.getMainLooper()) { // 需要 1 不需要2 invoke(subscribleMethod, activity, msg); } else { // post方法 执行在子线程 接受消息 在主线程 handler.post(new Runnable() { @Override public void run() { invoke(subscribleMethod, activity, msg); } }); } break; case PostThread: break; default: break; } } } } } /** *调用activity 的 @Subscribe(threadMode = ThreadMode.Async) public void receive(MessageBean messageBean ) / private void invoke(SubscribleMethod subscribleMethod, Object activity, Object mesg) { Method method = subscribleMethod.getMethod(); try { method.invoke(activity, mesg); } catch (IllegalAccessException e) { e.printStackTrace(); } catch (InvocationTargetException e) { e.printStackTrace(); }} 注:isAssignableFrom Determines if the class or interface represented by this * {@code Class} object is either the same as, or is a superclass or * superinterface of, the class or interface represented by the specified * {@code Class} parameter. It returns {@code true} if so; * otherwise it returns {@code false}. If this {@code Class} * object represents a primitive type, this method returns * {@code true} if the specified {@code Class} parameter is * exactly this {@code Class} object; otherwise it returns * {@code false}. 大概意思: 确定由这个@code Class对象所表示的类或接口是否与指定的@code Class参数所表示的类或接口相同，或者是超类或超接口。 如果是这样，它返回@code true;否则它会返回@code false。如果这个@code Class对象代表一个原始类型，那么如果指定的@code Class参数恰好是@code Class对象， 那么这个方法将返回@code true;否则它会返回@code false。 class1.isAssignableFrom(class2) 判定此 Class 对象所表示的类或接口与指定的 Class 参数所表示的类或接口是否相同，或是否是其超类或超接口。如果是则返回 true；否则返回 false。如果该 Class 表示一个基本类型，且指定的 Class 参数正是该 Class 对象，则该方法返回 true；否则返回 false。 1.class2是不是class1的子类或者子接口 2.Object是所有类的父类