文章主要内容为：
1.EventBus源码分析
2.手动实现一个简单版的EventBus
本文不再介绍EventBus的用法
- 首先来看看EventBus的入口
public static EventBus getDefault() {
if (defaultInstance == null) {
synchronized (EventBus.class) {
if (defaultInstance == null) {
defaultInstance = new EventBus();
}
}
}
return defaultInstance;
}
这里使用单例模式来创建EventBus实例，同时加锁，保证在不同线程中，EventBus的唯一
- 在看看EventBus注册的方法
public void register(Object subscriber) {
Class<?> subscriberClass = subscriber.getClass();
List<SubscriberMethod> subscriberMethods = subscriberMethodFinder.findSubscriberMethods(subscriberClass);
synchronized (this) {
for (SubscriberMethod subscriberMethod : subscriberMethods) {
subscribe(subscriber, subscriberMethod);
}
}
}
前两行代码的主要是先获取到订阅类的class，然后将class里面的methods存放到List<SubscriberMethod>，我们在这里主要看一下第二行代码的findSubscriberMethods()方法
- findSubscriberMethods()
List<SubscriberMethod> findSubscriberMethods(Class<?> subscriberClass) {
List<SubscriberMethod> subscriberMethods = METHOD_CACHE.get(subscriberClass);
if (subscriberMethods != null) {
return subscriberMethods;
}
if (ignoreGeneratedIndex) {
subscriberMethods = findUsingReflection(subscriberClass);
} else {
subscriberMethods = findUsingInfo(subscriberClass);
}
if (subscriberMethods.isEmpty()) {
throw new EventBusException("Subscriber " + subscriberClass
+ " and its super classes have no public methods with the @Subscribe annotation");
} else {
METHOD_CACHE.put(subscriberClass, subscriberMethods);
return subscriberMethods;
}
}
首先会在“METHOD_CACHE”这个数组里面查找是否有缓存过的method，ignoreGeneratedIndex默认为false，现在再往下面看看findUsingInfo()方法
- 比较关键的findUsingInfo()
private List<SubscriberMethod> findUsingInfo(Class<?> subscriberClass) {
FindState findState = prepareFindState();
findState.initForSubscriber(subscriberClass);
while (findState.clazz != null) {
findState.subscriberInfo = getSubscriberInfo(findState);
if (findState.subscriberInfo != null) {
SubscriberMethod[] array = findState.subscriberInfo.getSubscriberMethods();
for (SubscriberMethod subscriberMethod : array) {
if (findState.checkAdd(subscriberMethod.method, subscriberMethod.eventType)) {
findState.subscriberMethods.add(subscriberMethod);
}
}
} else {
findUsingReflectionInSingleClass(findState);
}
findState.moveToSuperclass();
}
return getMethodsAndRelease(findState);
}
这里用了FindState这个内部类来用于保存订阅者类的信息，以map的形式保存；接下来用initForSubscriber()这个方法进行初始化；然后再findUsingReflectionInSingleClass()在这个方法内，会使用反射，将你所有含有注解的方法从class里面遍历出来，并且保存在FindState的list当中，对于有注解但是不符合要求的，会通过异常抛出
- 看看最后一排的getMethodsAndRelease()方法
private List<SubscriberMethod> getMethodsAndRelease(FindState findState) {
List<SubscriberMethod> subscriberMethods = new ArrayList<>(findState.subscriberMethods);
findState.recycle();
synchronized (FIND_STATE_POOL) {
for (int i = 0; i < POOL_SIZE; i++) {
if (FIND_STATE_POOL[i] == null) {
FIND_STATE_POOL[i] = findState;
break;
}
}
}
return subscriberMethods;
}
getMethodsAndRelease()主要做的事情就是将findstate里面的method取出来;然后将findstate里面的map释放掉；最后将自己的引用赋给一个空FIND_STATE_POOL[i],起到复用池的效果
在regisert的最后,会调用subscribe()方法,这个方法主要是订阅的方法与事件进行注册
发送事件 post
public void post(Object event) {
PostingThreadState postingState = currentPostingThreadState.get();
List<Object> eventQueue = postingState.eventQueue;
eventQueue.add(event);
if (!postingState.isPosting) {
postingState.isMainThread = Looper.getMainLooper() == Looper.myLooper();
postingState.isPosting = true;
if (postingState.canceled) {
throw new EventBusException("Internal error. Abort state was not reset");
}
try {
while (!eventQueue.isEmpty()) {
postSingleEvent(eventQueue.remove(0), postingState);
}
} finally {
postingState.isPosting = false;
postingState.isMainThread = false;
}
}
}
PostingThreadState这个类主要是保存当前线程的信息，订阅者和订阅事件。这里post的流程是先从currentPostingThreadState获取当前线程信息，然后将当前线程的事件取出来，然后添加到队列里面等待分发；这里在循环队列中的事件的时候，也会循环当前事件的父类和接口，查找出所有的订阅者;最后会在postToSubscription()方法里面判断在那个线程里面执行方法，通过反射执行符合需求的包含注解的方法
好的，我们接下来用100多行代码 ，来实现eventbus的事件发送
-先写一个person对象
public class Person {
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
private String name;
private String sex;
public Person(String name, String sex) {
this.name = name;
this.sex = sex;
}
}
- 然后在写一个注解接口类
@Retention(RetentionPolicy.RUNTIME)
public @interface Subscribe {
ThreadMode threadMode() default ThreadMode.PostThread;
}
- 在写一个SubscriberMethod对象，里面用来存放订阅者的一些信息
public class SubscribleMethod {
//订阅事件的method对象
private Method method;
//订阅事件的线程位置
private ThreadMode threadMode;
//订阅事件类型
private Class<?> eventType;
public SubscribleMethod(Method method, ThreadMode threadMode, Class<?> eventType) {
this.method = method;
this.threadMode = threadMode;
this.eventType = eventType;
}
public Method getMethod() {
return method;
}
public ThreadMode getThreadMode() {
return threadMode;
}
public Class<?> getEventType() {
return eventType;
}
}
-在写一个枚举类，用于存放线程位置的标志，ThreadMode
public enum ThreadMode {
PostThread,
MainThread,
BackgroundThread,
Async
}
- 好了 接下来开始写eventbus的注册和发送事件
public class Eventbus {
private static Eventbus instance = new Eventbus();
public static Eventbus getDefault() {
return instance;
}
//这个map用于保存订阅者的信息
private Map<Object, List<SubscribleMethod>> cacheMap;
private Eventbus() {
this.cacheMap = new HashMap<>();
}
public void register(Object activity) {
Class<?> clazz = activity.getClass();
List<SubscribleMethod> list = cacheMap.get(activity);
//判断是否注册过
if (list == null) {
list = getSubscribleMethods(activity);
cacheMap.put(activity, list);
}
}
//获取activity下所有的订阅方法
private List<SubscribleMethod> getSubscribleMethods(Object activity) {
List<SubscribleMethod> list = new ArrayList<>();
Class clazz = activity.getClass();
while (clazz != null) {
String name = clazz.getName();
//如果包名是java javax android开头的 说明是系统的方法 直接跳过 节省事件
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;
}
//event只能接受一个参数
Class[] paratems = method.getParameterTypes();
if (paratems.length != 1) {
String methodName = method.getDeclaringClass().getName() + "." + method.getName();
throw new EventBusException("@Subscribe method " + methodName +
"must have exactly 1 parameter but has " + paratems.length);
}
//满足所有要求 找到所有的订阅方法 全部return出去
ThreadMode threadMode = subscribe.threadMode();
SubscribleMethod subscribleMethod = new SubscribleMethod(method
, threadMode, paratems[0]);
list.add(subscribleMethod);
}
clazz = clazz.getSuperclass();
}
return list;
}
public void post(final Object object) {
Set<Object> set = cacheMap.keySet();
Iterator iterator = set.iterator();
//遍历caheMap表中所有的订阅者
while (iterator.hasNext()) {
//获取到actiivty对象
final Object activity = iterator.next();
//获取activity下存放订阅者信息的list
List<SubscribleMethod> list = cacheMap.get(activity);
//遍历所有订阅者
for (final SubscribleMethod subscribleMethod : list) {
//判断订阅类型是不是一样的 如果是一样的就需要接受事件
if (subscribleMethod.getEventType().isAssignableFrom(object.getClass())) {
invoke(subscribleMethod, activity, object);
}
}
}
}
//反射发送事件
private void invoke(SubscribleMethod subscribleMethod, Object activity, Object object) {
Method method = subscribleMethod.getMethod();
try {
method.invoke(activity, object);
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
e.printStackTrace();
}
}
}
- 好了，所有代码写完了，现在在activity里面使用就行
//注册
Eventbus.getDefault().register(this);
//发送消息
Eventbus.getDefault().post(new Person("abc", "男"));
//接受消息
@Subscribe(threadMode = ThreadMode.MainThread)
public void receive(Person person ) {
Toast.makeText(this, person.getName()+"----"+person.getSex(), Toast.LENGTH_SHORT).show();
}
如果想要加上线程判断的话，在post方法里面通过subscribleMethod.getThreadMode()进行判断就行
