EventBus的简单使用与原理

EventBus是一款针对Android优化的发布/订阅事件总线。主要功能是替代Intent,Handler,BroadCast在Fragment，Activity，Service，线程之间传递消息.优点是开销小，代码更优雅。以及将发送者和接收者解耦。

部分源码：

//通过反射，获取到订阅者的所有方法
			Method[] methods = clazz.getMethods();
			for (Method method : methods) {
				String methodName = method.getName();
				//只找以onEvent开头的方法
				if (methodName.startsWith(eventMethodName)) {
					int modifiers = method.getModifiers();
					//判断订阅者是否是public的,并且是否有修饰符，看来订阅者只能是public的，并且不能被final，static等修饰
					if ((modifiers & Modifier.PUBLIC) != 0 && (modifiers & MODIFIERS_IGNORE) == 0) {
						//获得订阅函数的参数
						Class<?>[] parameterTypes = method.getParameterTypes();
						//看了参数的个数只能是1个
						if (parameterTypes.length == 1) {
							//获取onEvent后面的部分
							String modifierString = methodName.substring(eventMethodName.length());
							ThreadMode threadMode;
							if (modifierString.length() == 0) {
								//订阅函数为onEvnet
								//记录线程模型为PostThread,意义就是发布事件和接收事件在同一个线程执行，详细可以参考我对于四个订阅函数不同点分析
								threadMode = ThreadMode.PostThread;
							} else if (modifierString.equals("MainThread")) {
								//对应onEventMainThread
								threadMode = ThreadMode.MainThread;
							} else if (modifierString.equals("BackgroundThread")) {
								//对应onEventBackgrondThread
								threadMode = ThreadMode.BackgroundThread;
							} else if (modifierString.equals("Async")) {
								//对应onEventAsync
								threadMode = ThreadMode.Async;
							} else {
								if (skipMethodVerificationForClasses.containsKey(clazz)) {
									continue;
								} else {
									throw new EventBusException("Illegal onEvent method, check for typos: " + method);
								}
							}
							//获取参数类型，其实就是接收事件的类型
							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
								//封装一个订阅方法对象，这个对象包含Method对象，threadMode对象，eventType对象
								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);
					}
				}
			}
			//看了还会遍历父类的订阅函数
			clazz = clazz.getSuperclass();
		}
		//最后加入缓存，第二次使用直接从缓存拿
		if (subscriberMethods.isEmpty()) {
			throw new EventBusException("Subscriber " + subscriberClass + " has no public methods called "
					+ eventMethodName);
		} else {
			synchronized (methodCache) {
				methodCache.put(key, subscriberMethods);
			}
			return subscriberMethods;
		}
	}

更多源码见：http://www.tuicool.com/articles/jUvyUjB