EventBus是一款在 Android 开发中使用的发布/订阅事件总线框架，基于观察者模式.
2418741155-5d5209ae7054f_articlex.png
Evenbus用法很简单,只需要四步就能够实现
dependencies {
...
implementation 'org.greenrobot:eventbus:3.1.1'
}
1,注册
EventBus.getDefault().register(this);
2，注解
@Subscribe(threadMode = ThreadMode.MAIN)
public void receive(Friend friend){
Toast.makeText(this, friend.toString(), Toast.LENGTH_SHORT).show();
}
3,post(发布)
EventBus.getDefault().post(new Friend("Sven", 18));
4,反注册
EventBus.getDefault().unregister(this);
EventBus使用就是这么简单四步，下面我们来看看源码实现
1，register
public void register(Object subscriber) {
Class<?> subscriberClass = subscriber.getClass();
List<SubscriberMethod> subscriberMethods = subscriberMethodFinder.findSubscriberMethods(subscriberClass);
synchronized (this) {
for (SubscriberMethod subscriberMethod : subscriberMethods) {
subscribe(subscriber, subscriberMethod);
}
}
}
private void subscribe(Object subscriber, SubscriberMethod subscriberMethod) {
Class<?> eventType = subscriberMethod.eventType;
Subscription newSubscription = new Subscription(subscriber, subscriberMethod);
CopyOnWriteArrayList<Subscription> subscriptions = subscriptionsByEventType.get(eventType);
if (subscriptions == null) {
subscriptions = new CopyOnWriteArrayList<>();
subscriptionsByEventType.put(eventType, subscriptions);
} else {
if (subscriptions.contains(newSubscription)) {
throw new EventBusException("Subscriber " + subscriber.getClass() + " already registered to event "
+ eventType);
}
}
int size = subscriptions.size();
for (int i = 0; i <= size; i++) {
if (i == size || subscriberMethod.priority > subscriptions.get(i).subscriberMethod.priority) {
subscriptions.add(i, newSubscription);
break;
}
}
List<Class<?>> subscribedEvents = typesBySubscriber.get(subscriber);
if (subscribedEvents == null) {
subscribedEvents = new ArrayList<>();
typesBySubscriber.put(subscriber, subscribedEvents);
}
subscribedEvents.add(eventType);
if (subscriberMethod.sticky) {
if (eventInheritance) {
Set<Map.Entry<Class<?>, Object>> entries = stickyEvents.entrySet();
for (Map.Entry<Class<?>, Object> entry : entries) {
Class<?> candidateEventType = entry.getKey();
if (eventType.isAssignableFrom(candidateEventType)) {
Object stickyEvent = entry.getValue();
checkPostStickyEventToSubscription(newSubscription, stickyEvent);
}
}
} else {
Object stickyEvent = stickyEvents.get(eventType);
checkPostStickyEventToSubscription(newSubscription, stickyEvent);
}
}
}
简单来说，register就是将注册的对象的类的方法中符合条件的方法的详细信息（即有标注Subscribe注解等）保存在一个缓存subscriptionsByEventType中。
2， @Subscribe (threadMode = ThreadMode.MAIN)（注解）
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.METHOD})
public @interface Subscribe {
ThreadMode threadMode() default ThreadMode.POSTING;
/**
* If true, delivers the most recent sticky event (posted with
* {@link EventBus#postSticky(Object)}) to this subscriber (if event available).
*/
boolean sticky() default false;
/** Subscriber priority to influence the order of event delivery.
* Within the same delivery thread ({@link ThreadMode}), higher priority subscribers will receive events before
* others with a lower priority. The default priority is 0. Note: the priority does *NOT* affect the order of
* delivery among subscribers with different {@link ThreadMode}s! */
int priority() default 0;
}
注解用于Method上，主要作用是用这个来区别是否需要进行事件处理
ThreadMode：线程模式（用来指定线程）
POSTING：默认的模式,开销最小的模式,因为声明为POSTING的订阅者会在发布的同一个线程调用，发布者在主线程那么订阅者也就在主线程,反之亦,避免了线程切换,如果不确定是否有耗时操作，谨慎使用，因为可能是在主线程发布
MAIN：主线程调用，视发布线程不同处理不同,如果发布者在主线程那么直接调用(非阻塞式),如果发布者不在主线程那么阻塞式调用
MAIN_ORDERED：和MAIN差不多,主线程调用，和MAIN不同的是他保证了post是非阻塞式的(默认走MAIN的非主线程的逻辑，所以可以做到非阻塞)
BACKGROUND：在子线程调用,如果发布在子线程那么直接在发布线程调用,如果发布在主线程那么将开启一个子线程来调用,这个子线程是阻塞式的,按顺序交付所有事件,所以也不适合做耗时任务,因为多个事件共用这一个后台线程
ASYNC：在子线程调用,总是开启一个新的线程来调用,适用于做耗时任务,比如数据库操作,网络请求等，不适合做计算任务,会导致开启大量线程
3，post
public void post(Object event) {
PostingThreadState postingState = currentPostingThreadState.get();
List<Object> eventQueue = postingState.eventQueue;
eventQueue.add(event);
if (!postingState.isPosting) {
postingState.isMainThread = isMainThread();
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;
}
}
}
这个方法是将register注册在subscriptionsByEventType缓存集合中符合条件的方法进行反射调用，并通过上面的注解标注来找到用来处理事件的方法
4.unregister
从缓存中将注册的对象移除
public synchronized void unregister(Object subscriber) {
List<Class<?>> subscribedTypes = typesBySubscriber.get(subscriber);
if (subscribedTypes != null) {
for (Class<?> eventType : subscribedTypes) {
unsubscribeByEventType(subscriber, eventType);
}
typesBySubscriber.remove(subscriber);
} else {
logger.log(Level.WARNING, "Subscriber to unregister was not registered before: " + subscriber.getClass());
}
}
画图分析
eventbus_wps.jpg
根据源码分析我们可以自己手写一个EventBus的架构（当然是简化的版本，但是功能却完全相同）。
//注册
public void register(Object subscriber) {
Class<?> aClass = subscriber.getClass();
List<SubscribleMethod> subscribleMethods = cacheMap.get(subscriber);
//如果已经注册，就不需要注册
if (subscribleMethods == null) {
subscribleMethods = getSubscribleMethods(subscriber);
cacheMap.put(subscriber, subscribleMethods);
}
}
//遍历能够接收事件的方法
private List<SubscribleMethod> getSubscribleMethods(Object subscriber) {
List<SubscribleMethod> list = new ArrayList<>();
Class<?> aClass = subscriber.getClass();
//需要 subscriber --- 》BaseActivity ------->Activitiy 往父类一直找
while (aClass != null) {
//判断分类是在那个包下，（如果是系统的就不需要）
String name = aClass.getName();
if (name.startsWith("java.") ||
name.startsWith("javax.") ||
name.startsWith("android.") ||
name.startsWith("androidx.")) {
break;
}
Method[] declaredMethods = aClass.getDeclaredMethods();
//遍历类下面的所有方法，找到标有注解的能够接收事件的方法
for (Method method : declaredMethods) {
HGSubscribe annotation = method.getAnnotation(HGSubscribe.class);
if (annotation == null) {
continue;
}
//检测这个方法合不合格
Class<?>[] parameterTypes = method.getParameterTypes();
if (parameterTypes.length != 1) {
throw new RuntimeException("eventbus只能接收一个参数");
}
//符合要求
HGThreadMode dnThreadMode = annotation.threadMode();
SubscribleMethod subscribleMethod = new SubscribleMethod(method, dnThreadMode, parameterTypes[0]);
list.add(subscribleMethod);
}
//自己找不到，就往父类找，一直找下去看能不能找到能够接收事件的方法
aClass = aClass.getSuperclass();
}
return list;
}
//发布事件
public void post(final Object obj) {
Set<Object> set = cacheMap.keySet();
Iterator<Object> iterator = set.iterator();
while (iterator.hasNext()) {
//拿到注册类
final Object next = iterator.next();
//获取类中所有添加注解的方法
List<SubscribleMethod> list = cacheMap.get(next);
for (final SubscribleMethod subscribleMethod : list) {
//判断这个方法是否应该接收事件
if (subscribleMethod.getEventType().isAssignableFrom(obj.getClass())) {
switch (subscribleMethod.getThreadMode()) {
case MAIN:
//如果接收方法在主线程执行的情况
if(Looper.myLooper() == Looper.getMainLooper()){
invoke(subscribleMethod, next, obj);
} else {
//post方法执行在子线程中，接收消息在主线程中
handler.post(new Runnable() {
@Override
public void run() {
invoke(subscribleMethod, next, obj);
}
});
}
break;
//接收方法在子线程种情况
case ASYNC:
//post方法执行在主线程中
if(Looper.myLooper() == Looper.getMainLooper()){
executorService.execute(new Runnable() {
@Override
public void run() {
invoke(subscribleMethod, next, obj);
}
});
} else {
//post方法执行在子线程中
invoke(subscribleMethod, next, obj);
}
break;
case POSTING:
break;
}
}
}
}
}
//反射调用接收事件的方法
private void invoke(SubscribleMethod subscribleMethod, Object next, Object obj) {
Method method = subscribleMethod.getMethod();
try {
method.invoke(next, obj);
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
e.printStackTrace();
}
}
//取消注册
public void unregister(Object subscriber) {
Class<?> aClass = subscriber.getClass();
List<SubscribleMethod> list = cacheMap.get(subscriber);
//如果获取到
if (list != null) {
cacheMap.remove(subscriber);
}
}
项目地址：https://github.com/games2sven/HG_EventBus
手写实现HermesEventBus架构
上面的项目只是一个简单的EventBus架构，假设我现在需要跨进程实现事件通信，那么可以加入饿了么跨进程通信框架Hermes。
我们知道，跨进程通信在android中需要用AIDL来实现。
第一步：定义AIDL文件
image-20200528163602766.png
image-20200528163705440.png
image-20200528163732140.png
第二步：开始正式编写代码
1，服务端注册
//初始化
Hermes.getDefault().init(this);
//注册 进程A中，被进程B调用的类需要事先注册
Hermes.getDefault().register(HgUserManager.class);
//生成类的单例对象
HgUserManager.getInstance().setFriend(new Friend("Sven",18));
public void init(Context context){
this.mContext = context.getApplicationContext();
}
//----------服务端------A进程-----------
public void register(Class<HgUserManager> clazz) {
typeCenter.register(clazz);
}
TypeCenter.class
public void register(Class<HgUserManager> clazz) {
//注册---类 注册----方法
registerClass(clazz);
registerMethod(clazz);
}
private void registerMethod(Class<HgUserManager> clazz) {
Method[] methods = clazz.getMethods();
for (Method method : methods) {
mRawMethods.putIfAbsent(clazz,new ConcurrentHashMap<String, Method>());
ConcurrentHashMap<String,Method> map = mRawMethods.get(clazz);
String methodId = TypeUtils.getMethodId(method);
map.put(methodId,method);
}
}
private void registerClass(Class<HgUserManager> clazz) {
String name = clazz.getName();
mAnnotatedClasses.putIfAbsent(name,clazz);
}
HgUserManager添加注解@ClassId，并实现IUserManager暴露getFriend和setFriend接口为之后B进程通过AIDL能够调用到
@ClassId("com.highgreat.sven.myapplication.manager.HgUserManager")
public class HgUserManager implements IUserManager{
Friend friend;
private static HgUserManager sInstance = null;
private HgUserManager(){
}
//约定这个进程A 单例对象的 规则 getInstance()
public static synchronized HgUserManager getInstance(){
if(sInstance == null){
sInstance = new HgUserManager();
}
return sInstance;
}
@Override
public Friend getFriend() {
return friend;
}
@Override
public void setFriend(Friend friend) {
this.friend = friend;
}
}
定义运行时注解ClassId
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface ClassId {
String value();
}
2，客户端连接
Hermes.getDefault().connect(this, HermesService.class);
//----------客户端--------B进程-----------
public void connect(Context context, Class< ? extends HermesService> hermesServiceClass) {
connectApp(context,null,hermesServiceClass);
}
private void connectApp(Context context, String packageName, Class<? extends HermesService> hermesServiceClass) {
init(context);
serviceConnectionManager.bind(context.getApplicationContext(),packageName,hermesServiceClass);
}
ServiceConnectionManager.class
public void bind(Context context, String packageName, Class<? extends HermesService> hermesServiceClass){
HermesServiceConnection hermesServiceConnection = new HermesServiceConnection(hermesServiceClass);
mHermesServiceConnection.put(hermesServiceClass,hermesServiceConnection);
Intent intent;
if(TextUtils.isEmpty(packageName)){
intent = new Intent(context,hermesServiceClass);
}else{
intent = new Intent();
intent.setClassName(packageName,hermesServiceClass.getName());
}
// 开启AIDL服务
context.bindService(intent,hermesServiceConnection,Context.BIND_AUTO_CREATE);
}
private class HermesServiceConnection implements ServiceConnection{
private Class<? extends HermesService> mClass;
HermesServiceConnection(Class<? extends HermesService> service){this.mClass = service;};
@Override
public void onServiceConnected(ComponentName name, IBinder service) {
MyEventBusService myEventBusService = MyEventBusService.Stub.asInterface(service);
//AIDL服务连接成功，保存起来
mHermesServices.put(mClass,myEventBusService);
}
@Override
public void onServiceDisconnected(ComponentName name) {
//AIDL连接断开，移除缓存
mHermesServices.remove(mClass);
}
}
HermesService.class
public class HermesService extends Service{
@Override
public IBinder onBind(Intent intent) {
return mBinder;
}
//AIDL接口 通过Binder机制拿到服务端的对象
private MyEventBusService.Stub mBinder = new MyEventBusService.Stub() {
@Override
public Responce send(Request request) throws RemoteException {
//队请求参数进行处理 生成Responce结果返回
ResponceMake responceMake = null;
switch (request.getType()){
case Hermes.TYPE_GET://获取单例
responceMake = new InstanceResponceMake();
break;
case Hermes.TYPE_NEW:
responceMake = new ObjectResponceMake();
break;
}
return responceMake.makeResponce(request);
}
};
}
3，通信
//客户端得到服务端的单例对象
userManager = Hermes.getDefault().getInstance(IUserManager.class);
Toast.makeText(this,"-----> "+userManager.getFriend().toString(), Toast.LENGTH_SHORT).show();
Hermes.class
//主要防止方法重载 单例对象
public <T> T getInstance(Class<T> clazz,Object... parameters){
Responce responce = sendRequest(HermesService.class,clazz,null,parameters);
return getProxy(HermesService.class,clazz);
}
private <T> T getProxy(Class<? extends HermesService> service, Class clazz) {
ClassLoader classLoader = service.getClassLoader();
T proxy = (T) Proxy.newProxyInstance(classLoader,new Class<?>[]{clazz},new HermesInvocationHandler(service,clazz));
return proxy;
}
private <T> Responce sendRequest(Class<HermesService> hermesServiceClass,
Class<T> clazz, Method method,Object[] parameters){
RequestBean requestBean = new RequestBean();
if(clazz.getAnnotation(ClassId.class) == null){
requestBean.setClassName(clazz.getName());
requestBean.setResultClassName(clazz.getName());
}else{
//返回类型的全类名
requestBean.setClassName(clazz.getAnnotation(ClassId.class).value());
requestBean.setResultClassName(clazz.getAnnotation(ClassId.class).value());
}
if(method != null){
//方法名 统一传 方法名+参数名
requestBean.setMethodName(TypeUtils.getMethodId(method));
}
RequestParameter[] requestParameters = null;
if(parameters != null && parameters.length >0){
requestParameters = new RequestParameter[parameters.length];
for(int i = 0;i<parameters.length;i++){
Object parameter = parameters[i];
String parameterClassName = parameter.getClass().getName();
String parameterValue = GSON.toJson(parameter);
RequestParameter requestParameter = new RequestParameter(parameterClassName,parameterValue);
requestParameters[i] = requestParameter;
}
}
if(requestParameters != null){
requestBean.setRequestParameters(requestParameters);
}
//请求获取单例代理对象---------》调用对象的方法 B进程开始请求A进程的通信
Request request = new Request(GSON.toJson(requestBean),TYPE_GET);
return serviceConnectionManager.request(hermesServiceClass,request);
}
sendRequest是在获取单例对象的时候(即Hermes.getDefault().getInstance(IUserManager.class))会去调用AIDL实现跨进程通信。
ServiceConnectionManager.java
public Responce request(Class<HermesService> hermesServiceClass, Request request){
//从缓存中获取binder代理对象，发送请求
MyEventBusService eventBusService = mHermesServices.get(hermesServiceClass);
if(eventBusService != null){
try {
//这里是B进程通过Binder代理机制发送数据给A进程，并收到回复
//调用的是AIDL接口方法
Responce responce = eventBusService.send(request);
return responce;
} catch (RemoteException e) {
e.printStackTrace();
}
}
return null;
}
HermesInvocationHandler.class
public class HermesInvocationHandler implements InvocationHandler {
private static final String TAG = "Sven";
private Class clazz;
private Class hermeService;
private static final Gson GSON = new Gson();
public HermesInvocationHandler(Class<? extends HermesService> service,Class clazz){
this.clazz = clazz;
this.hermeService = service;
}
//当执行代理类的方法（比如getFriend()）时会走到这里来
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
Log.i(TAG, "invoke:-------> " + method.getName());
Responce responce = Hermes.getDefault().sendObjectRequest(hermeService,clazz,method,args);
if(!TextUtils.isEmpty(responce.getData())){
ResponceBean responceBean = GSON.fromJson(responce.getData(),ResponceBean.class);
if(responceBean.getData() != null){
Object getUserResult = responceBean.getData();
String data = GSON.toJson(getUserResult);
Class stringgetUser = method.getReturnType();
Object o = GSON.fromJson(data,stringgetUser);
return o;
}
}
return null;
}
}
Hermes.java
public <T> Responce sendObjectRequest(Class<HermesService> hermesServiceClass
, Class<T> clazz, Method method, Object[] parameters) {
RequestBean requestBean = new RequestBean();
String className = null;
if(clazz.getAnnotation(ClassId.class) == null){
requestBean.setClassName(clazz.getName());
requestBean.setResultClassName(clazz.getName());
}else{
requestBean.setClassName(clazz.getAnnotation(ClassId.class).value());
requestBean.setResultClassName(clazz.getAnnotation(ClassId.class).value());
}
if(method != null){
requestBean.setMethodName(TypeUtils.getMethodId(method));
}
RequestParameter[] requestParameters = null;
if (parameters != null && parameters.length > 0) {
requestParameters = new RequestParameter[parameters.length];
for (int i = 0; i < parameters.length; i++) {
Object parameter = parameters[i];
String parameterClassName = parameter.getClass().getName();
String parameterValue = GSON.toJson(parameter);
RequestParameter requestParameter = new RequestParameter(parameterClassName, parameterValue);
requestParameters[i] = requestParameter;
}
}
if (requestParameters != null) {
requestBean.setRequestParameter(requestParameters);
}
// 请求获取单例 ----》对象 ----------》调用对象的方法
Request request = new Request(GSON.toJson(requestBean),TYPE_NEW);
return serviceConnectionManager.request(hermesServiceClass, request);
}
sendObjectRequest在代理对象调用方法时会进行通信，即userManager.getFriend()时会去走AIDL接口方法实现跨进程通信。
Request.java
package com.highgreat.sven.myapplication;
import android.os.Parcel;
import android.os.Parcelable;
public class Request implements Parcelable{
//请求的对象 RequestBean对应的jason字符串
private String data;
//请求对象的类型
private int type;
//反序列化 A进程
protected Request(Parcel in) {
data = in.readString();
type = in.readInt();
}
public Request(String data, int type) {
this.data = data;
this.type = type;
}
public String getData() {
return data;
}
public int getType() {
return type;
}
public static final Creator<Request> CREATOR = new Creator<Request>() {
@Override
public Request createFromParcel(Parcel in) {
return new Request(in);
}
@Override
public Request[] newArray(int size) {
return new Request[size];
}
};
@Override
public int describeContents() {
return 0;
}
//序列化
@Override
public void writeToParcel(Parcel dest, int flags) {
dest.writeString(data);
dest.writeInt(type);
}
}
Responce.java
package com.highgreat.sven.myapplication;
import android.os.Parcel;
import android.os.Parcelable;
public class Responce implements Parcelable {
private String data;
public String getData() {
return data;
}
protected Responce(Parcel in) {
data = in.readString();
}
public Responce(String data) {
this.data = data;
}
public static final Creator<Responce> CREATOR = new Creator<Responce>() {
@Override
public Responce createFromParcel(Parcel in) {
return new Responce(in);
}
@Override
public Responce[] newArray(int size) {
return new Responce[size];
}
};
@Override
public int describeContents() {
return 0;
}
@Override
public void writeToParcel(Parcel dest, int flags) {
dest.writeString(data);
}
}
流程图：
hermes跨进程调用.png
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