EvenBus for Android 之 订阅者注册
EventBus中的订阅者其实就是具体的方法他的注册过程分为以下几步：
1、在类中找到要注册的方法
2、把找到的方法注册到EventBus中
在类中找到要注册的方法：
先上一段 SubscriberMethodFinder类中查找订阅者方法的代码
List<SubscriberMethod> findSubscriberMethods(Class<?> subscriberClass, String eventMethodName) {
String key = subscriberClass.getName() + '.' + eventMethodName;
List<SubscriberMethod> subscriberMethods;
synchronized (methodCache) {
subscriberMethods = methodCache.get(key);
}
if (subscriberMethods != null) {
return subscriberMethods;
}
subscriberMethods = new ArrayList<SubscriberMethod>();
Class<?> clazz = subscriberClass;
HashSet<String> eventTypesFound = new HashSet<String>();
StringBuilder methodKeyBuilder = new StringBuilder();
while (clazz != null) {
String name = clazz.getName();
if (name.startsWith("java.") || name.startsWith("javax.") || name.startsWith("android.")) {
// Skip system classes, this just degrades performance
break;
}
// Starting with EventBus 2.2 we enforced methods to be public (might change with annotations again)
Method[] methods = clazz.getMethods();
for (Method method : methods) {
String methodName = method.getName();
if (methodName.startsWith(eventMethodName)) {
int modifiers = method.getModifiers();
if ((modifiers & Modifier.PUBLIC) != 0 && (modifiers & MODIFIERS_IGNORE) == 0) {
Class<?>[] parameterTypes = method.getParameterTypes();
if (parameterTypes.length == 1) {
String modifierString = methodName.substring(eventMethodName.length());
ThreadMode threadMode;
if (modifierString.length() == 0) {
threadMode = ThreadMode.PostThread;
} else if (modifierString.equals("MainThread")) {
threadMode = ThreadMode.MainThread;
} else if (modifierString.equals("BackgroundThread")) {
threadMode = ThreadMode.BackgroundThread;
} else if (modifierString.equals("Async")) {
threadMode = ThreadMode.Async;
} else {
if (skipMethodVerificationForClasses.containsKey(clazz)) {
continue;
} else {
throw new EventBusException("Illegal onEvent method, check for typos: " + method);
}
}
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
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);
}
}
}
clazz = clazz.getSuperclass();
}
if (subscriberMethods.isEmpty()) {
throw new EventBusException("Subscriber " + subscriberClass + " has no public methods called "
+ eventMethodName);
} else {
synchronized (methodCache) {
methodCache.put(key, subscriberMethods);
}
return subscriberMethods;
}
}
通过这个方法可以看到，需要传2个参数，Class subscriberClass和String eventMethodName
subscriberClass是包含订阅者方法的类，可以获取到该类中的所有方法，
eventMethodName是约定作为订阅者的方法的前缀，通过这个来过滤出事订阅者的方法
接下在看下具体实现
String key = subscriberClass.getName() + '.' + eventMethodName;
List<SubscriberMethod> subscriberMethods;
synchronized (methodCache) {
subscriberMethods = methodCache.get(key);
}
if (subscriberMethods != null) {
return subscriberMethods;
}
通过类名和eventMethodName组成一个key，在一个静态的methodCache中查找是否已经存在要找的该类下的订阅者，不存在就得进行下面的解析
String name = clazz.getName();
if (name.startsWith("java.") || name.startsWith("javax.") || name.startsWith("android.")) {
// Skip system classes, this just degrades performance
break;
}
对要解析的类进行判断，排除是系统的类
if (methodName.startsWith(eventMethodName)) {
int modifiers = method.getModifiers();
if ((modifiers & Modifier.PUBLIC) != 0 && (modifiers & MODIFIERS_IGNORE) == 0) {
Class<?>[] parameterTypes = method.getParameterTypes();
if (parameterTypes.length == 1) {
String modifierString = methodName.substring(eventMethodName.length());
ThreadMode threadMode;
if (modifierString.length() == 0) {
threadMode = ThreadMode.PostThread;
} else if (modifierString.equals("MainThread")) {
threadMode = ThreadMode.MainThread;
} else if (modifierString.equals("BackgroundThread")) {
threadMode = ThreadMode.BackgroundThread;
} else if (modifierString.equals("Async")) {
threadMode = ThreadMode.Async;
} else {
if (skipMethodVerificationForClasses.containsKey(clazz)) {
continue;
} else {
throw new EventBusException("Illegal onEvent method, check for typos: " + method);
}
}
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
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);
}
}
}
遍历该类下的方法，找出是eventMethodName前缀的方法，在通过方法名称定义订阅者的线程类型
PostThread，订阅者将在发起事件的同一个线程中执行
MainThread，订阅者将在主线程中执行
BackgroupThread，订阅者将在一个后台线程中执行，如果发送的线程不是主线程，则直接在发起时间的线程中执行，如果发送的线程是主线程，则会在唯一的一个后台线程中按照顺序来执行所有的后台时间响应函数
AsyncThread，订阅者将在另一个异步线程中执行
if (subscriberMethods.isEmpty()) {
throw new EventBusException("Subscriber " + subscriberClass + " has no public methods called "
+ eventMethodName);
} else {
synchronized (methodCache) {
methodCache.put(key, subscriberMethods);
}
return subscriberMethods;
}
把获取去到的订阅者保存到methodCache中。