android 事件总线 -- Otto(六) Bus

前端时间，由于出差在外，博客停更了很长一段时间，从今天开始，继续开始更新博客。

之前我们研究了Otto的其它几部分的源码，而我们在使用的过程中，最常用也是直接使用的其实是Bus这个类，今天就来从源码的角度看看Bus类。

Bus

分发事件给事件监听器，并且提供事件监听器的注册方法。下面我们从使用的角度来学习源码。

在我们使用的时候，首先是要构建Bus类，来看看构造方法。

/** Creates a new Bus named "default" that enforces actions on the main thread   * 创建默认的构造方法，传递一个默认的身份标识   */  public Bus() {    this(DEFAULT_IDENTIFIER);  }  /**   * Creates a new Bus with the given {@code identifier} that enforces actions on the main thread.   * 创建一个运行在主线程的Bus   *   * @param identifier a brief name for this bus, for debugging purposes.  Should be a valid Java identifier.   *  identifier 的作用是一个对于bus的名称标识，作为调试用。   */  public Bus(String identifier) {    this(ThreadEnforcer.MAIN, identifier);  }  /**   * Creates a new Bus named "default" with the given {@code enforcer} for actions.   * 创建一个运行在自定义线程的Bus   * @param enforcer Thread enforcer for register, unregister, and post actions.   */  public Bus(ThreadEnforcer enforcer) {    this(enforcer, DEFAULT_IDENTIFIER);  }  /**   * Creates a new Bus with the given {@code enforcer} for actions and the given {@code identifier}.   *   * @param enforcer Thread enforcer for register, unregister, and post actions.   * @param identifier A brief name for this bus, for debugging purposes.  Should be a valid Java identifier.   */  public Bus(ThreadEnforcer enforcer, String identifier) {    this(enforcer, identifier, HandlerFinder.ANNOTATED);  }  /**   * Test constructor which allows replacing the default {@code HandlerFinder}.   *   * @param enforcer Thread enforcer for register, unregister, and post actions.   * @param identifier A brief name for this bus, for debugging purposes.  Should be a valid Java identifier.   * @param handlerFinder Used to discover event handlers and producers when registering/unregistering an object.   */  Bus(ThreadEnforcer enforcer, String identifier, HandlerFinder handlerFinder) {    this.enforcer =  enforcer;    this.identifier = identifier;    this.handlerFinder = handlerFinder;  }

在上面的构造方法中，有两个参数

ThreadEnforcer -- 这个是确保bus运行在指定的线程。在前面已经讲过了，如果还没看过的，可以点击 ThreadEnforcer  进行查看。

HandlerFinder -- 这个是用来提前事件生产者和操作者的注册和取消注册的，之前也讲过，可以点击 查看

构造过后，我们需要在注册。

@Override   protected void onResume() {    super.onResume();    // Register ourselves so that we can provide the initial value.    BusProvider.getInstance().register(this);  }

其中用到了register，下面我们来看看Bus中的register：

public void register(Object object) {    if (object == null) {      throw new NullPointerException("Object to register must not be null.");    }    // 确保运行的线程    enforcer.enforce(this);        // 发现所有的生产者(@Producer注释的函数)    Map<Class<?>, EventProducer> foundProducers = handlerFinder.findAllProducers(object);    for (Class<?> type : foundProducers.keySet()) {      final EventProducer producer = foundProducers.get(type);      EventProducer previousProducer = producersByType.putIfAbsent(type, producer);      //checking if the previous producer existed      if (previousProducer != null) {        throw new IllegalArgumentException("Producer method for type " + type          + " found on type " + producer.target.getClass()          + ", but already registered by type " + previousProducer.target.getClass() + ".");      }      Set<EventHandler> handlers = handlersByType.get(type);      if (handlers != null && !handlers.isEmpty()) {        for (EventHandler handler : handlers) {          dispatchProducerResultToHandler(handler, producer);        }      }    }    // 获取所有的订阅者(@Subscribe)    Map<Class<?>, Set<EventHandler>> foundHandlersMap = handlerFinder.findAllSubscribers(object);    for (Class<?> type : foundHandlersMap.keySet()) {      Set<EventHandler> handlers = handlersByType.get(type);      if (handlers == null) {        //concurrent put if absent        Set<EventHandler> handlersCreation = new CopyOnWriteArraySet<EventHandler>();        handlers = handlersByType.putIfAbsent(type, handlersCreation);        if (handlers == null) {            handlers = handlersCreation;        }      }      final Set<EventHandler> foundHandlers = foundHandlersMap.get(type);      if (!handlers.addAll(foundHandlers)) {        throw new IllegalArgumentException("Object already registered.");      }    }        // 分发生产者到处理器    for (Map.Entry<Class<?>, Set<EventHandler>> entry : foundHandlersMap.entrySet()) {      Class<?> type = entry.getKey();      EventProducer producer = producersByType.get(type);      if (producer != null && producer.isValid()) {        Set<EventHandler> foundHandlers = entry.getValue();        for (EventHandler foundHandler : foundHandlers) {          if (!producer.isValid()) {            break;          }          if (foundHandler.isValid()) {            dispatchProducerResultToHandler(foundHandler, producer);          }        }      }    }  }

思路其实也挺简单的，就是首先获取所有的@Producer注释的方法，然后获取所有的@Subscribe注释的函数，最后将两者关联起来，这样，在调用post()方法时，就能实现数据传递的效果了。

之后就是unregister方法：

public void unregister(Object object) {    if (object == null) {      throw new NullPointerException("Object to unregister must not be null.");    }    enforcer.enforce(this);    Map<Class<?>, EventProducer> producersInListener = handlerFinder.findAllProducers(object);    for (Map.Entry<Class<?>, EventProducer> entry : producersInListener.entrySet()) {      final Class<?> key = entry.getKey();      EventProducer producer = getProducerForEventType(key);      EventProducer value = entry.getValue();      if (value == null || !value.equals(producer)) {        throw new IllegalArgumentException(            "Missing event producer for an annotated method. Is " + object.getClass()                + " registered?");      }      producersByType.remove(key).invalidate();    }    Map<Class<?>, Set<EventHandler>> handlersInListener = handlerFinder.findAllSubscribers(object);    for (Map.Entry<Class<?>, Set<EventHandler>> entry : handlersInListener.entrySet()) {      Set<EventHandler> currentHandlers = getHandlersForEventType(entry.getKey());      Collection<EventHandler> eventMethodsInListener = entry.getValue();      if (currentHandlers == null || !currentHandlers.containsAll(eventMethodsInListener)) {        throw new IllegalArgumentException(            "Missing event handler for an annotated method. Is " + object.getClass()                + " registered?");      }      for (EventHandler handler : currentHandlers) {        if (eventMethodsInListener.contains(handler)) {          handler.invalidate();        }      }      currentHandlers.removeAll(eventMethodsInListener);    }  }

在之前的register的时候，用的是put方法，现在调用的是remove方法。