RxJava替代EventBus：RxBus

简要说明

关于RxJava：https://github.com/ReactiveX/RxJava
关于EventBus：https://github.com/greenrobot/EventBus
由于最近工程中依赖于RxAndroid与RxJava，因此以RxJava模式实现EventBus相同的API，移除重复功能的依赖，达到精简工程的目的。

第一步：构造单例

1. 在EventBus中

EventBus.getDefault();

2. 构造RxBus相同的API

public class RxBus {    
      private static volatile RxBus instance;    
      private RxBus() {}    
      public static RxBus getDefault() {        
         if (instance == null) {           
             synchronized (RxBus.class) {                
                 if (instance == null) {                    
                     instance = new RxBus();                
                 }            
              }        
         }        
         return instance;    
      }

3. 在RxBus中

RxBus.getDefault();

第二步：事件注解

1. 在EventBus中

@Subscribe
public void onMessageEvent(MessageEvent event) {/* Do something */};

2. 构造RxBus相同的API

public class RxBus { 

      //省略第一步...

      @Target(ElementType.METHOD)
      @Retention(RetentionPolicy.RUNTIME)
      public @interface Subscribe {}
}

3. 在RxBus中

@RxBus.Subscribe
public void onMessageEvent(MessageEvent event) {/* Do something */};

第三步：订阅事件

1. 在EventBus中

@Override
public void onStart() { 
      super.onStart(); 
      EventBus.getDefault().register(this);
}

2. 构造RxBus相同的API

public class RxBus { 

      //省略第一步...

      private final Subject<Object, Object> bus = new SerializedSubject<>(PublishSubject.create());
      private final ArrayMap<String, List<Subscription>> subscriptionArray = new ArrayMap<>();
      
      public void register(final Object observable) {    
          boolean isRegisterSuccess = false;    
          final String subscriptionKey = observable.getClass().getName();
          //反射获取方法列表  
          Method[] methods = observable.getClass().getMethods();    
          for (Method method : methods) {    
              //如果方法不存在Subscribe注解则不做处理
              if (!method.isAnnotationPresent(Subscribe.class)) continue;        
              final Method subscriptionMethod = method;
              //获取方法参数类型，即：MessageEvent.class
              Class<?> key = method.getParameterTypes()[0];
              //订阅MessageEvent.class类型实例，ofType作用已filter相近
              Subscription subscription = bus.ofType(key).subscribe(new Action1<Object>() {
                  @Override            
                  public void call(Object value) {
                      try {
                          //反射赋值，即传递事件值
                          subscriptionMethod.setAccessible(true);
                          subscriptionMethod.invoke(observable, value);
                      } catch (IllegalAccessException | InvocationTargetException e) { 
                          throw new RuntimeException(subscriptionKey + " isn't allowed to register!");
                      }
                  }
              });
              //存储订阅实例列表，用于后续解除注册
              List<Subscription> subscriptions;
              if (subscriptionArray.containsKey(subscriptionKey)) {
                 subscriptions = subscriptionArray.get(subscriptionKey);
              } else {
                 subscriptions = new ArrayList<>();
              }
              subscriptions.add(subscription);
              subscriptionArray.put(subscriptionKey, subscriptions); 
              isRegisterSuccess = true;
          }
          //如果注册的类中不存在Subscribe注解方法，则抛出异常提醒
          if (!isRegisterSuccess) 
              throw new RuntimeException(subscriptionKey + " has no any RxBuxSubscribe Event!");
      }

      //省略第二步...
}

3. 在RxBus中

@Override
public void onStart() { 
      super.onStart(); 
      RxBus.getDefault().register(this);
}

取消订阅

1. 在EventBus中

@Override
public void onStop() { 
      super.onStop(); 
      EventBus.getDefault().unregister(this);
}

2. 构造RxBus相同的API

public class RxBus { 

      //省略第一步...
      //省略第三步...

      public void unregister(Object observable) {    
          String subscriptionKey = observable.getClass().getName();
          if (!subscriptionArray.containsKey(subscriptionKey)) return;
          List<Subscription> subscriptions = subscriptionArray.get(subscriptionKey);
          for (Subscription subscription : subscriptions) {
              //如果已订阅，则取消订阅
              if (!subscription.isUnsubscribed()) subscription.unsubscribe();
          }
          subscriptionArray.remove(subscriptionKey);
      }      

      //省略第二步...
}

3. 在RxBus中

@Override
public void onStop() { 
      super.onStop(); 
      RxBus.getDefault().unregister(this);
}

发送事件

1. 在EventBus中

EventBus.getDefault().post(new MessageEvent());

2. 构造RxBus相同的API

public class RxBus { 

      //省略第一步...
      //省略第三步...
      //省略第四步...     
      
      public void post (Object event) { 
          bus.onNext(event);
      }

      //省略第二步...
}

3. 在RxBus中

RxBus.getDefault().post(new MessageEvent());

关于ThreadMode

在订阅时根据需要使用RxJava的Schedulers即可。